aarch64-linux-gnu-4.9/share/doc/gcc/Warning-Options.html - toolchains/linux-x86/gcc - Git at Google

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 <a name="Warning-Options"></a>
 <div class="header">
 <p>
 Next: <a href="Debugging-Options.html#Debugging-Options" accesskey="n" rel="next">Debugging Options</a>, Previous: <a href="Language-Independent-Options.html#Language-Independent-Options" accesskey="p" rel="prev">Language Independent Options</a>, Up: <a href="Invoking-GCC.html#Invoking-GCC" accesskey="u" rel="up">Invoking GCC</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
 </div>
 <hr>
 <a name="Options-to-Request-or-Suppress-Warnings"></a>
 <h3 class="section">3.8 Options to Request or Suppress Warnings</h3>
 <a name="index-options-to-control-warnings"></a>
 <a name="index-warning-messages"></a>
 <a name="index-messages_002c-warning"></a>
 <a name="index-suppressing-warnings"></a>

 <p>Warnings are diagnostic messages that report constructions that
 are not inherently erroneous but that are risky or suggest there
 may have been an error.
 </p>
 <p>The following language-independent options do not enable specific
 warnings but control the kinds of diagnostics produced by GCC.
 </p>
 <dl compact="compact">
 <dd><a name="index-syntax-checking"></a>
 </dd>
 <dt><code>-fsyntax-only</code></dt>
 <dd><a name="index-fsyntax_002donly"></a>
 <p>Check the code for syntax errors, but don&rsquo;t do anything beyond that.
 </p>
 </dd>
 <dt><code>-fmax-errors=<var>n</var></code></dt>
 <dd><a name="index-fmax_002derrors"></a>
 <p>Limits the maximum number of error messages to <var>n</var>, at which point
 GCC bails out rather than attempting to continue processing the source
 code.  If <var>n</var> is 0 (the default), there is no limit on the number
 of error messages produced.  If <samp>-Wfatal-errors</samp> is also
 specified, then <samp>-Wfatal-errors</samp> takes precedence over this
 option.
 </p>
 </dd>
 <dt><code>-w</code></dt>
 <dd><a name="index-w"></a>
 <p>Inhibit all warning messages.
 </p>
 </dd>
 <dt><code>-Werror</code></dt>
 <dd><a name="index-Werror"></a>
 <a name="index-Wno_002derror"></a>
 <p>Make all warnings into errors.
 </p>
 </dd>
 <dt><code>-Werror=</code></dt>
 <dd><a name="index-Werror_003d"></a>
 <a name="index-Wno_002derror_003d"></a>
 <p>Make the specified warning into an error.  The specifier for a warning
 is appended; for example <samp>-Werror=switch</samp> turns the warnings
 controlled by <samp>-Wswitch</samp> into errors.  This switch takes a
 negative form, to be used to negate <samp>-Werror</samp> for specific
 warnings; for example <samp>-Wno-error=switch</samp> makes
 <samp>-Wswitch</samp> warnings not be errors, even when <samp>-Werror</samp>
 is in effect.
 </p>
 <p>The warning message for each controllable warning includes the
 option that controls the warning.  That option can then be used with
 <samp>-Werror=</samp> and <samp>-Wno-error=</samp> as described above.
 (Printing of the option in the warning message can be disabled using the
 <samp>-fno-diagnostics-show-option</samp> flag.)
 </p>
 <p>Note that specifying <samp>-Werror=</samp><var>foo</var> automatically implies
 <samp>-W</samp><var>foo</var>.  However, <samp>-Wno-error=</samp><var>foo</var> does not
 imply anything.
 </p>
 </dd>
 <dt><code>-Wfatal-errors</code></dt>
 <dd><a name="index-Wfatal_002derrors"></a>
 <a name="index-Wno_002dfatal_002derrors"></a>
 <p>This option causes the compiler to abort compilation on the first error
 occurred rather than trying to keep going and printing further error
 messages.
 </p>
 </dd>
 </dl>

 <p>You can request many specific warnings with options beginning with
 &lsquo;<samp>-W</samp>&rsquo;, for example <samp>-Wimplicit</samp> to request warnings on
 implicit declarations.  Each of these specific warning options also
 has a negative form beginning &lsquo;<samp>-Wno-</samp>&rsquo; to turn off warnings; for
 example, <samp>-Wno-implicit</samp>.  This manual lists only one of the
 two forms, whichever is not the default.  For further
 language-specific options also refer to <a href="C_002b_002b-Dialect-Options.html#C_002b_002b-Dialect-Options">C++ Dialect Options</a> and
 <a href="Objective_002dC-and-Objective_002dC_002b_002b-Dialect-Options.html#Objective_002dC-and-Objective_002dC_002b_002b-Dialect-Options">Objective-C and Objective-C++ Dialect Options</a>.
 </p>
 <p>When an unrecognized warning option is requested (e.g.,
 <samp>-Wunknown-warning</samp>), GCC emits a diagnostic stating
 that the option is not recognized.  However, if the <samp>-Wno-</samp> form
 is used, the behavior is slightly different: no diagnostic is
 produced for <samp>-Wno-unknown-warning</samp> unless other diagnostics
 are being produced.  This allows the use of new <samp>-Wno-</samp> options
 with old compilers, but if something goes wrong, the compiler
 warns that an unrecognized option is present.
 </p>
 <dl compact="compact">
 <dt><code>-Wpedantic</code></dt>
 <dt><code>-pedantic</code></dt>
 <dd><a name="index-pedantic-1"></a>
 <a name="index-Wpedantic"></a>
 <p>Issue all the warnings demanded by strict ISO C and ISO C++;
 reject all programs that use forbidden extensions, and some other
 programs that do not follow ISO C and ISO C++.  For ISO C, follows the
 version of the ISO C standard specified by any <samp>-std</samp> option used.
 </p>
 <p>Valid ISO C and ISO C++ programs should compile properly with or without
 this option (though a rare few require <samp>-ansi</samp> or a
 <samp>-std</samp> option specifying the required version of ISO C).  However,
 without this option, certain GNU extensions and traditional C and C++
 features are supported as well.  With this option, they are rejected.
 </p>
 <p><samp>-Wpedantic</samp> does not cause warning messages for use of the
 alternate keywords whose names begin and end with &lsquo;<samp>__</samp>&rsquo;.  Pedantic
 warnings are also disabled in the expression that follows
 <code>__extension__</code>.  However, only system header files should use
 these escape routes; application programs should avoid them.
 See <a href="Alternate-Keywords.html#Alternate-Keywords">Alternate Keywords</a>.
 </p>
 <p>Some users try to use <samp>-Wpedantic</samp> to check programs for strict ISO
 C conformance.  They soon find that it does not do quite what they want:
 it finds some non-ISO practices, but not all&mdash;only those for which
 ISO C <em>requires</em> a diagnostic, and some others for which
 diagnostics have been added.
 </p>
 <p>A feature to report any failure to conform to ISO C might be useful in
 some instances, but would require considerable additional work and would
 be quite different from <samp>-Wpedantic</samp>.  We don&rsquo;t have plans to
 support such a feature in the near future.
 </p>
 <p>Where the standard specified with <samp>-std</samp> represents a GNU
 extended dialect of C, such as &lsquo;<samp>gnu90</samp>&rsquo; or &lsquo;<samp>gnu99</samp>&rsquo;, there is a
 corresponding <em>base standard</em>, the version of ISO C on which the GNU
 extended dialect is based.  Warnings from <samp>-Wpedantic</samp> are given
 where they are required by the base standard.  (It does not make sense
 for such warnings to be given only for features not in the specified GNU
 C dialect, since by definition the GNU dialects of C include all
 features the compiler supports with the given option, and there would be
 nothing to warn about.)
 </p>
 </dd>
 <dt><code>-pedantic-errors</code></dt>
 <dd><a name="index-pedantic_002derrors-1"></a>
 <p>Like <samp>-Wpedantic</samp>, except that errors are produced rather than
 warnings.
 </p>
 </dd>
 <dt><code>-Wall</code></dt>
 <dd><a name="index-Wall"></a>
 <a name="index-Wno_002dall"></a>
 <p>This enables all the warnings about constructions that some users
 consider questionable, and that are easy to avoid (or modify to
 prevent the warning), even in conjunction with macros.  This also
 enables some language-specific warnings described in <a href="C_002b_002b-Dialect-Options.html#C_002b_002b-Dialect-Options">C++ Dialect Options</a> and <a href="Objective_002dC-and-Objective_002dC_002b_002b-Dialect-Options.html#Objective_002dC-and-Objective_002dC_002b_002b-Dialect-Options">Objective-C and Objective-C++ Dialect Options</a>.
 </p>
 <p><samp>-Wall</samp> turns on the following warning flags:
 </p>
 <div class="smallexample">
 <pre class="smallexample">-Waddress
 -Warray-bounds <span class="roman">(only with</span> <samp>-O2</samp><span class="roman">)</span>
 -Wc++11-compat
 -Wchar-subscripts
 -Wenum-compare <span class="roman">(in C/ObjC; this is on by default in C++)</span>
 -Wimplicit-int <span class="roman">(C and Objective-C only)</span>
 -Wimplicit-function-declaration <span class="roman">(C and Objective-C only)</span>
 -Wcomment
 -Wformat
 -Wmain <span class="roman">(only for C/ObjC and unless</span> <samp>-ffreestanding</samp><span class="roman">)</span>
 -Wmaybe-uninitialized
 -Wmissing-braces <span class="roman">(only for C/ObjC)</span>
 -Wnonnull
 -Wopenmp-simd
 -Wparentheses
 -Wpointer-sign
 -Wreorder
 -Wreturn-type
 -Wsequence-point
 -Wsign-compare <span class="roman">(only in C++)</span>
 -Wstrict-aliasing
 -Wstrict-overflow=1
 -Wswitch
 -Wtrigraphs
 -Wuninitialized
 -Wunknown-pragmas
 -Wunused-function
 -Wunused-label
 -Wunused-value
 -Wunused-variable
 -Wvolatile-register-var

 </pre></div>

 <p>Note that some warning flags are not implied by <samp>-Wall</samp>.  Some of
 them warn about constructions that users generally do not consider
 questionable, but which occasionally you might wish to check for;
 others warn about constructions that are necessary or hard to avoid in
 some cases, and there is no simple way to modify the code to suppress
 the warning. Some of them are enabled by <samp>-Wextra</samp> but many of
 them must be enabled individually.
 </p>
 </dd>
 <dt><code>-Wextra</code></dt>
 <dd><a name="index-W"></a>
 <a name="index-Wextra"></a>
 <a name="index-Wno_002dextra"></a>
 <p>This enables some extra warning flags that are not enabled by
 <samp>-Wall</samp>. (This option used to be called <samp>-W</samp>.  The older
 name is still supported, but the newer name is more descriptive.)
 </p>
 <div class="smallexample">
 <pre class="smallexample">-Wclobbered
 -Wempty-body
 -Wignored-qualifiers
 -Wmissing-field-initializers
 -Wmissing-parameter-type <span class="roman">(C only)</span>
 -Wold-style-declaration <span class="roman">(C only)</span>
 -Woverride-init
 -Wsign-compare
 -Wtype-limits
 -Wuninitialized
 -Wunused-parameter <span class="roman">(only with</span> <samp>-Wunused</samp> <span class="roman">or</span> <samp>-Wall</samp><span class="roman">)</span>
 -Wunused-but-set-parameter <span class="roman">(only with</span> <samp>-Wunused</samp> <span class="roman">or</span> <samp>-Wall</samp><span class="roman">)</span>

 </pre></div>

 <p>The option <samp>-Wextra</samp> also prints warning messages for the
 following cases:
 </p>
 <ul>
 <li> A pointer is compared against integer zero with &lsquo;<samp>&lt;</samp>&rsquo;, &lsquo;<samp>&lt;=</samp>&rsquo;,
 &lsquo;<samp>&gt;</samp>&rsquo;, or &lsquo;<samp>&gt;=</samp>&rsquo;.

 </li><li> (C++ only) An enumerator and a non-enumerator both appear in a
 conditional expression.

 </li><li> (C++ only) Ambiguous virtual bases.

 </li><li> (C++ only) Subscripting an array that has been declared &lsquo;<samp>register</samp>&rsquo;.

 </li><li> (C++ only) Taking the address of a variable that has been declared
 &lsquo;<samp>register</samp>&rsquo;.

 </li><li> (C++ only) A base class is not initialized in a derived class&rsquo;s copy
 constructor.

 </li></ul>

 </dd>
 <dt><code>-Wchar-subscripts</code></dt>
 <dd><a name="index-Wchar_002dsubscripts"></a>
 <a name="index-Wno_002dchar_002dsubscripts"></a>
 <p>Warn if an array subscript has type <code>char</code>.  This is a common cause
 of error, as programmers often forget that this type is signed on some
 machines.
 This warning is enabled by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wcomment</code></dt>
 <dd><a name="index-Wcomment"></a>
 <a name="index-Wno_002dcomment"></a>
 <p>Warn whenever a comment-start sequence &lsquo;<samp>/*</samp>&rsquo; appears in a &lsquo;<samp>/*</samp>&rsquo;
 comment, or whenever a Backslash-Newline appears in a &lsquo;<samp>//</samp>&rsquo; comment.
 This warning is enabled by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wno-coverage-mismatch</code></dt>
 <dd><a name="index-Wno_002dcoverage_002dmismatch"></a>
 <p>Warn if feedback profiles do not match when using the
 <samp>-fprofile-use</samp> option.
 If a source file is changed between compiling with <samp>-fprofile-gen</samp> and
 with <samp>-fprofile-use</samp>, the files with the profile feedback can fail
 to match the source file and GCC cannot use the profile feedback
 information.  By default, this warning is enabled and is treated as an
 error.  <samp>-Wno-coverage-mismatch</samp> can be used to disable the
 warning or <samp>-Wno-error=coverage-mismatch</samp> can be used to
 disable the error.  Disabling the error for this warning can result in
 poorly optimized code and is useful only in the
 case of very minor changes such as bug fixes to an existing code-base.
 Completely disabling the warning is not recommended.
 </p>
 </dd>
 <dt><code>-Wno-cpp</code></dt>
 <dd><p><span class="roman">(C, Objective-C, C++, Objective-C++ and Fortran only)</span>
 </p>
 <p>Suppress warning messages emitted by <code>#warning</code> directives.
 </p>
 </dd>
 <dt><code>-Wdouble-promotion <span class="roman">(C, C++, Objective-C and Objective-C++ only)</span></code></dt>
 <dd><a name="index-Wdouble_002dpromotion"></a>
 <a name="index-Wno_002ddouble_002dpromotion"></a>
 <p>Give a warning when a value of type <code>float</code> is implicitly
 promoted to <code>double</code>.  CPUs with a 32-bit &ldquo;single-precision&rdquo;
 floating-point unit implement <code>float</code> in hardware, but emulate
 <code>double</code> in software.  On such a machine, doing computations
 using <code>double</code> values is much more expensive because of the
 overhead required for software emulation.
 </p>
 <p>It is easy to accidentally do computations with <code>double</code> because
 floating-point literals are implicitly of type <code>double</code>.  For
 example, in:
 </p><div class="smallexample">
 <pre class="smallexample">float area(float radius)
 {
    return 3.14159 * radius * radius;
 }
 </pre></div>
 <p>the compiler performs the entire computation with <code>double</code>
 because the floating-point literal is a <code>double</code>.
 </p>
 </dd>
 <dt><code>-Wformat</code></dt>
 <dt><code>-Wformat=<var>n</var></code></dt>
 <dd><a name="index-Wformat"></a>
 <a name="index-Wno_002dformat"></a>
 <a name="index-ffreestanding-2"></a>
 <a name="index-fno_002dbuiltin-1"></a>
 <a name="index-Wformat_003d"></a>
 <p>Check calls to <code>printf</code> and <code>scanf</code>, etc., to make sure that
 the arguments supplied have types appropriate to the format string
 specified, and that the conversions specified in the format string make
 sense.  This includes standard functions, and others specified by format
 attributes (see <a href="Function-Attributes.html#Function-Attributes">Function Attributes</a>), in the <code>printf</code>,
 <code>scanf</code>, <code>strftime</code> and <code>strfmon</code> (an X/Open extension,
 not in the C standard) families (or other target-specific families).
 Which functions are checked without format attributes having been
 specified depends on the standard version selected, and such checks of
 functions without the attribute specified are disabled by
 <samp>-ffreestanding</samp> or <samp>-fno-builtin</samp>.
 </p>
 <p>The formats are checked against the format features supported by GNU
 libc version 2.2.  These include all ISO C90 and C99 features, as well
 as features from the Single Unix Specification and some BSD and GNU
 extensions.  Other library implementations may not support all these
 features; GCC does not support warning about features that go beyond a
 particular library&rsquo;s limitations.  However, if <samp>-Wpedantic</samp> is used
 with <samp>-Wformat</samp>, warnings are given about format features not
 in the selected standard version (but not for <code>strfmon</code> formats,
 since those are not in any version of the C standard).  See <a href="C-Dialect-Options.html#C-Dialect-Options">Options Controlling C Dialect</a>.
 </p>
 <dl compact="compact">
 <dt><code>-Wformat=1</code></dt>
 <dt><code>-Wformat</code></dt>
 <dd><a name="index-Wformat-1"></a>
 <a name="index-Wformat_003d1"></a>
 <p>Option <samp>-Wformat</samp> is equivalent to <samp>-Wformat=1</samp>, and
 <samp>-Wno-format</samp> is equivalent to <samp>-Wformat=0</samp>.  Since
 <samp>-Wformat</samp> also checks for null format arguments for several
 functions, <samp>-Wformat</samp> also implies <samp>-Wnonnull</samp>.  Some
 aspects of this level of format checking can be disabled by the
 options: <samp>-Wno-format-contains-nul</samp>,
 <samp>-Wno-format-extra-args</samp>, and <samp>-Wno-format-zero-length</samp>.
 <samp>-Wformat</samp> is enabled by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wno-format-contains-nul</code></dt>
 <dd><a name="index-Wno_002dformat_002dcontains_002dnul"></a>
 <a name="index-Wformat_002dcontains_002dnul"></a>
 <p>If <samp>-Wformat</samp> is specified, do not warn about format strings that
 contain NUL bytes.
 </p>
 </dd>
 <dt><code>-Wno-format-extra-args</code></dt>
 <dd><a name="index-Wno_002dformat_002dextra_002dargs"></a>
 <a name="index-Wformat_002dextra_002dargs"></a>
 <p>If <samp>-Wformat</samp> is specified, do not warn about excess arguments to a
 <code>printf</code> or <code>scanf</code> format function.  The C standard specifies
 that such arguments are ignored.
 </p>
 <p>Where the unused arguments lie between used arguments that are
 specified with &lsquo;<samp>$</samp>&rsquo; operand number specifications, normally
 warnings are still given, since the implementation could not know what
 type to pass to <code>va_arg</code> to skip the unused arguments.  However,
 in the case of <code>scanf</code> formats, this option suppresses the
 warning if the unused arguments are all pointers, since the Single
 Unix Specification says that such unused arguments are allowed.
 </p>
 </dd>
 <dt><code>-Wno-format-zero-length</code></dt>
 <dd><a name="index-Wno_002dformat_002dzero_002dlength"></a>
 <a name="index-Wformat_002dzero_002dlength"></a>
 <p>If <samp>-Wformat</samp> is specified, do not warn about zero-length formats.
 The C standard specifies that zero-length formats are allowed.
 </p>

 </dd>
 <dt><code>-Wformat=2</code></dt>
 <dd><a name="index-Wformat_003d2"></a>
 <p>Enable <samp>-Wformat</samp> plus additional format checks.  Currently
 equivalent to <samp>-Wformat -Wformat-nonliteral -Wformat-security
 -Wformat-y2k</samp>.
 </p>
 </dd>
 <dt><code>-Wformat-nonliteral</code></dt>
 <dd><a name="index-Wformat_002dnonliteral"></a>
 <a name="index-Wno_002dformat_002dnonliteral"></a>
 <p>If <samp>-Wformat</samp> is specified, also warn if the format string is not a
 string literal and so cannot be checked, unless the format function
 takes its format arguments as a <code>va_list</code>.
 </p>
 </dd>
 <dt><code>-Wformat-security</code></dt>
 <dd><a name="index-Wformat_002dsecurity"></a>
 <a name="index-Wno_002dformat_002dsecurity"></a>
 <p>If <samp>-Wformat</samp> is specified, also warn about uses of format
 functions that represent possible security problems.  At present, this
 warns about calls to <code>printf</code> and <code>scanf</code> functions where the
 format string is not a string literal and there are no format arguments,
 as in <code>printf (foo);</code>.  This may be a security hole if the format
 string came from untrusted input and contains &lsquo;<samp>%n</samp>&rsquo;.  (This is
 currently a subset of what <samp>-Wformat-nonliteral</samp> warns about, but
 in future warnings may be added to <samp>-Wformat-security</samp> that are not
 included in <samp>-Wformat-nonliteral</samp>.)
 </p>
 </dd>
 <dt><code>-Wformat-y2k</code></dt>
 <dd><a name="index-Wformat_002dy2k"></a>
 <a name="index-Wno_002dformat_002dy2k"></a>
 <p>If <samp>-Wformat</samp> is specified, also warn about <code>strftime</code>
 formats that may yield only a two-digit year.
 </p></dd>
 </dl>

 </dd>
 <dt><code>-Wnonnull</code></dt>
 <dd><a name="index-Wnonnull"></a>
 <a name="index-Wno_002dnonnull"></a>
 <p>Warn about passing a null pointer for arguments marked as
 requiring a non-null value by the <code>nonnull</code> function attribute.
 </p>
 <p><samp>-Wnonnull</samp> is included in <samp>-Wall</samp> and <samp>-Wformat</samp>.  It
 can be disabled with the <samp>-Wno-nonnull</samp> option.
 </p>
 </dd>
 <dt><code>-Winit-self <span class="roman">(C, C++, Objective-C and Objective-C++ only)</span></code></dt>
 <dd><a name="index-Winit_002dself"></a>
 <a name="index-Wno_002dinit_002dself"></a>
 <p>Warn about uninitialized variables that are initialized with themselves.
 Note this option can only be used with the <samp>-Wuninitialized</samp> option.
 </p>
 <p>For example, GCC warns about <code>i</code> being uninitialized in the
 following snippet only when <samp>-Winit-self</samp> has been specified:
 </p><div class="smallexample">
 <pre class="smallexample">int f()
 {
   int i = i;
   return i;
 }
 </pre></div>

 <p>This warning is enabled by <samp>-Wall</samp> in C++.
 </p>
 </dd>
 <dt><code>-Wimplicit-int <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Wimplicit_002dint"></a>
 <a name="index-Wno_002dimplicit_002dint"></a>
 <p>Warn when a declaration does not specify a type.
 This warning is enabled by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wimplicit-function-declaration <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Wimplicit_002dfunction_002ddeclaration"></a>
 <a name="index-Wno_002dimplicit_002dfunction_002ddeclaration"></a>
 <p>Give a warning whenever a function is used before being declared. In
 C99 mode (<samp>-std=c99</samp> or <samp>-std=gnu99</samp>), this warning is
 enabled by default and it is made into an error by
 <samp>-pedantic-errors</samp>. This warning is also enabled by
 <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wimplicit <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Wimplicit"></a>
 <a name="index-Wno_002dimplicit"></a>
 <p>Same as <samp>-Wimplicit-int</samp> and <samp>-Wimplicit-function-declaration</samp>.
 This warning is enabled by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wignored-qualifiers <span class="roman">(C and C++ only)</span></code></dt>
 <dd><a name="index-Wignored_002dqualifiers"></a>
 <a name="index-Wno_002dignored_002dqualifiers"></a>
 <p>Warn if the return type of a function has a type qualifier
 such as <code>const</code>.  For ISO C such a type qualifier has no effect,
 since the value returned by a function is not an lvalue.
 For C++, the warning is only emitted for scalar types or <code>void</code>.
 ISO C prohibits qualified <code>void</code> return types on function
 definitions, so such return types always receive a warning
 even without this option.
 </p>
 <p>This warning is also enabled by <samp>-Wextra</samp>.
 </p>
 </dd>
 <dt><code>-Wmain</code></dt>
 <dd><a name="index-Wmain"></a>
 <a name="index-Wno_002dmain"></a>
 <p>Warn if the type of &lsquo;<samp>main</samp>&rsquo; is suspicious.  &lsquo;<samp>main</samp>&rsquo; should be
 a function with external linkage, returning int, taking either zero
 arguments, two, or three arguments of appropriate types.  This warning
 is enabled by default in C++ and is enabled by either <samp>-Wall</samp>
 or <samp>-Wpedantic</samp>.
 </p>
 </dd>
 <dt><code>-Wmissing-braces</code></dt>
 <dd><a name="index-Wmissing_002dbraces"></a>
 <a name="index-Wno_002dmissing_002dbraces"></a>
 <p>Warn if an aggregate or union initializer is not fully bracketed.  In
 the following example, the initializer for &lsquo;<samp>a</samp>&rsquo; is not fully
 bracketed, but that for &lsquo;<samp>b</samp>&rsquo; is fully bracketed.  This warning is
 enabled by <samp>-Wall</samp> in C.
 </p>
 <div class="smallexample">
 <pre class="smallexample">int a[2][2] = { 0, 1, 2, 3 };
 int b[2][2] = { { 0, 1 }, { 2, 3 } };
 </pre></div>

 <p>This warning is enabled by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wmissing-include-dirs <span class="roman">(C, C++, Objective-C and Objective-C++ only)</span></code></dt>
 <dd><a name="index-Wmissing_002dinclude_002ddirs"></a>
 <a name="index-Wno_002dmissing_002dinclude_002ddirs"></a>
 <p>Warn if a user-supplied include directory does not exist.
 </p>
 </dd>
 <dt><code>-Wparentheses</code></dt>
 <dd><a name="index-Wparentheses"></a>
 <a name="index-Wno_002dparentheses"></a>
 <p>Warn if parentheses are omitted in certain contexts, such
 as when there is an assignment in a context where a truth value
 is expected, or when operators are nested whose precedence people
 often get confused about.
 </p>
 <p>Also warn if a comparison like &lsquo;<samp>x&lt;=y&lt;=z</samp>&rsquo; appears; this is
 equivalent to &lsquo;<samp>(x&lt;=y ? 1 : 0) &lt;= z</samp>&rsquo;, which is a different
 interpretation from that of ordinary mathematical notation.
 </p>
 <p>Also warn about constructions where there may be confusion to which
 <code>if</code> statement an <code>else</code> branch belongs.  Here is an example of
 such a case:
 </p>
 <div class="smallexample">
 <pre class="smallexample">{
   if (a)
     if (b)
       foo ();
   else
     bar ();
 }
 </pre></div>

 <p>In C/C++, every <code>else</code> branch belongs to the innermost possible
 <code>if</code> statement, which in this example is <code>if (b)</code>.  This is
 often not what the programmer expected, as illustrated in the above
 example by indentation the programmer chose.  When there is the
 potential for this confusion, GCC issues a warning when this flag
 is specified.  To eliminate the warning, add explicit braces around
 the innermost <code>if</code> statement so there is no way the <code>else</code>
 can belong to the enclosing <code>if</code>.  The resulting code
 looks like this:
 </p>
 <div class="smallexample">
 <pre class="smallexample">{
   if (a)
     {
       if (b)
         foo ();
       else
         bar ();
     }
 }
 </pre></div>

 <p>Also warn for dangerous uses of the GNU extension to
 <code>?:</code> with omitted middle operand. When the condition
 in the <code>?</code>: operator is a boolean expression, the omitted value is
 always 1.  Often programmers expect it to be a value computed
 inside the conditional expression instead.
 </p>
 <p>This warning is enabled by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wsequence-point</code></dt>
 <dd><a name="index-Wsequence_002dpoint"></a>
 <a name="index-Wno_002dsequence_002dpoint"></a>
 <p>Warn about code that may have undefined semantics because of violations
 of sequence point rules in the C and C++ standards.
 </p>
 <p>The C and C++ standards define the order in which expressions in a C/C++
 program are evaluated in terms of <em>sequence points</em>, which represent
 a partial ordering between the execution of parts of the program: those
 executed before the sequence point, and those executed after it.  These
 occur after the evaluation of a full expression (one which is not part
 of a larger expression), after the evaluation of the first operand of a
 <code>&amp;&amp;</code>, <code>||</code>, <code>? :</code> or <code>,</code> (comma) operator, before a
 function is called (but after the evaluation of its arguments and the
 expression denoting the called function), and in certain other places.
 Other than as expressed by the sequence point rules, the order of
 evaluation of subexpressions of an expression is not specified.  All
 these rules describe only a partial order rather than a total order,
 since, for example, if two functions are called within one expression
 with no sequence point between them, the order in which the functions
 are called is not specified.  However, the standards committee have
 ruled that function calls do not overlap.
 </p>
 <p>It is not specified when between sequence points modifications to the
 values of objects take effect.  Programs whose behavior depends on this
 have undefined behavior; the C and C++ standards specify that &ldquo;Between
 the previous and next sequence point an object shall have its stored
 value modified at most once by the evaluation of an expression.
 Furthermore, the prior value shall be read only to determine the value
 to be stored.&rdquo;.  If a program breaks these rules, the results on any
 particular implementation are entirely unpredictable.
 </p>
 <p>Examples of code with undefined behavior are <code>a = a++;</code>, <code>a[n]
 = b[n++]</code> and <code>a[i++] = i;</code>.  Some more complicated cases are not
 diagnosed by this option, and it may give an occasional false positive
 result, but in general it has been found fairly effective at detecting
 this sort of problem in programs.
 </p>
 <p>The standard is worded confusingly, therefore there is some debate
 over the precise meaning of the sequence point rules in subtle cases.
 Links to discussions of the problem, including proposed formal
 definitions, may be found on the GCC readings page, at
 <a href="http://gcc.gnu.org/readings.html">http://gcc.gnu.org/readings.html</a>.
 </p>
 <p>This warning is enabled by <samp>-Wall</samp> for C and C++.
 </p>
 </dd>
 <dt><code>-Wno-return-local-addr</code></dt>
 <dd><a name="index-Wno_002dreturn_002dlocal_002daddr"></a>
 <a name="index-Wreturn_002dlocal_002daddr"></a>
 <p>Do not warn about returning a pointer (or in C++, a reference) to a
 variable that goes out of scope after the function returns.
 </p>
 </dd>
 <dt><code>-Wreturn-type</code></dt>
 <dd><a name="index-Wreturn_002dtype"></a>
 <a name="index-Wno_002dreturn_002dtype"></a>
 <p>Warn whenever a function is defined with a return type that defaults
 to <code>int</code>.  Also warn about any <code>return</code> statement with no
 return value in a function whose return type is not <code>void</code>
 (falling off the end of the function body is considered returning
 without a value), and about a <code>return</code> statement with an
 expression in a function whose return type is <code>void</code>.
 </p>
 <p>For C++, a function without return type always produces a diagnostic
 message, even when <samp>-Wno-return-type</samp> is specified.  The only
 exceptions are &lsquo;<samp>main</samp>&rsquo; and functions defined in system headers.
 </p>
 <p>This warning is enabled by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wswitch</code></dt>
 <dd><a name="index-Wswitch"></a>
 <a name="index-Wno_002dswitch"></a>
 <p>Warn whenever a <code>switch</code> statement has an index of enumerated type
 and lacks a <code>case</code> for one or more of the named codes of that
 enumeration.  (The presence of a <code>default</code> label prevents this
 warning.)  <code>case</code> labels outside the enumeration range also
 provoke warnings when this option is used (even if there is a
 <code>default</code> label).
 This warning is enabled by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wswitch-default</code></dt>
 <dd><a name="index-Wswitch_002ddefault"></a>
 <a name="index-Wno_002dswitch_002ddefault"></a>
 <p>Warn whenever a <code>switch</code> statement does not have a <code>default</code>
 case.
 </p>
 </dd>
 <dt><code>-Wswitch-enum</code></dt>
 <dd><a name="index-Wswitch_002denum"></a>
 <a name="index-Wno_002dswitch_002denum"></a>
 <p>Warn whenever a <code>switch</code> statement has an index of enumerated type
 and lacks a <code>case</code> for one or more of the named codes of that
 enumeration.  <code>case</code> labels outside the enumeration range also
 provoke warnings when this option is used.  The only difference
 between <samp>-Wswitch</samp> and this option is that this option gives a
 warning about an omitted enumeration code even if there is a
 <code>default</code> label.
 </p>
 </dd>
 <dt><code>-Wsync-nand <span class="roman">(C and C++ only)</span></code></dt>
 <dd><a name="index-Wsync_002dnand"></a>
 <a name="index-Wno_002dsync_002dnand"></a>
 <p>Warn when <code>__sync_fetch_and_nand</code> and <code>__sync_nand_and_fetch</code>
 built-in functions are used.  These functions changed semantics in GCC 4.4.
 </p>
 </dd>
 <dt><code>-Wtrigraphs</code></dt>
 <dd><a name="index-Wtrigraphs"></a>
 <a name="index-Wno_002dtrigraphs"></a>
 <p>Warn if any trigraphs are encountered that might change the meaning of
 the program (trigraphs within comments are not warned about).
 This warning is enabled by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wunused-but-set-parameter</code></dt>
 <dd><a name="index-Wunused_002dbut_002dset_002dparameter"></a>
 <a name="index-Wno_002dunused_002dbut_002dset_002dparameter"></a>
 <p>Warn whenever a function parameter is assigned to, but otherwise unused
 (aside from its declaration).
 </p>
 <p>To suppress this warning use the &lsquo;<samp>unused</samp>&rsquo; attribute
 (see <a href="Variable-Attributes.html#Variable-Attributes">Variable Attributes</a>).
 </p>
 <p>This warning is also enabled by <samp>-Wunused</samp> together with
 <samp>-Wextra</samp>.
 </p>
 </dd>
 <dt><code>-Wunused-but-set-variable</code></dt>
 <dd><a name="index-Wunused_002dbut_002dset_002dvariable"></a>
 <a name="index-Wno_002dunused_002dbut_002dset_002dvariable"></a>
 <p>Warn whenever a local variable is assigned to, but otherwise unused
 (aside from its declaration).
 This warning is enabled by <samp>-Wall</samp>.
 </p>
 <p>To suppress this warning use the &lsquo;<samp>unused</samp>&rsquo; attribute
 (see <a href="Variable-Attributes.html#Variable-Attributes">Variable Attributes</a>).
 </p>
 <p>This warning is also enabled by <samp>-Wunused</samp>, which is enabled
 by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wunused-function</code></dt>
 <dd><a name="index-Wunused_002dfunction"></a>
 <a name="index-Wno_002dunused_002dfunction"></a>
 <p>Warn whenever a static function is declared but not defined or a
 non-inline static function is unused.
 This warning is enabled by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wunused-label</code></dt>
 <dd><a name="index-Wunused_002dlabel"></a>
 <a name="index-Wno_002dunused_002dlabel"></a>
 <p>Warn whenever a label is declared but not used.
 This warning is enabled by <samp>-Wall</samp>.
 </p>
 <p>To suppress this warning use the &lsquo;<samp>unused</samp>&rsquo; attribute
 (see <a href="Variable-Attributes.html#Variable-Attributes">Variable Attributes</a>).
 </p>
 </dd>
 <dt><code>-Wunused-local-typedefs <span class="roman">(C, Objective-C, C++ and Objective-C++ only)</span></code></dt>
 <dd><a name="index-Wunused_002dlocal_002dtypedefs"></a>
 <p>Warn when a typedef locally defined in a function is not used.
 This warning is enabled by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wunused-parameter</code></dt>
 <dd><a name="index-Wunused_002dparameter"></a>
 <a name="index-Wno_002dunused_002dparameter"></a>
 <p>Warn whenever a function parameter is unused aside from its declaration.
 </p>
 <p>To suppress this warning use the &lsquo;<samp>unused</samp>&rsquo; attribute
 (see <a href="Variable-Attributes.html#Variable-Attributes">Variable Attributes</a>).
 </p>
 </dd>
 <dt><code>-Wno-unused-result</code></dt>
 <dd><a name="index-Wunused_002dresult"></a>
 <a name="index-Wno_002dunused_002dresult"></a>
 <p>Do not warn if a caller of a function marked with attribute
 <code>warn_unused_result</code> (see <a href="Function-Attributes.html#Function-Attributes">Function Attributes</a>) does not use
 its return value. The default is <samp>-Wunused-result</samp>.
 </p>
 </dd>
 <dt><code>-Wunused-variable</code></dt>
 <dd><a name="index-Wunused_002dvariable"></a>
 <a name="index-Wno_002dunused_002dvariable"></a>
 <p>Warn whenever a local variable or non-constant static variable is unused
 aside from its declaration.
 This warning is enabled by <samp>-Wall</samp>.
 </p>
 <p>To suppress this warning use the &lsquo;<samp>unused</samp>&rsquo; attribute
 (see <a href="Variable-Attributes.html#Variable-Attributes">Variable Attributes</a>).
 </p>
 </dd>
 <dt><code>-Wunused-value</code></dt>
 <dd><a name="index-Wunused_002dvalue"></a>
 <a name="index-Wno_002dunused_002dvalue"></a>
 <p>Warn whenever a statement computes a result that is explicitly not
 used. To suppress this warning cast the unused expression to
 &lsquo;<samp>void</samp>&rsquo;. This includes an expression-statement or the left-hand
 side of a comma expression that contains no side effects. For example,
 an expression such as &lsquo;<samp>x[i,j]</samp>&rsquo; causes a warning, while
 &lsquo;<samp>x[(void)i,j]</samp>&rsquo; does not.
 </p>
 <p>This warning is enabled by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wunused</code></dt>
 <dd><a name="index-Wunused"></a>
 <a name="index-Wno_002dunused"></a>
 <p>All the above <samp>-Wunused</samp> options combined.
 </p>
 <p>In order to get a warning about an unused function parameter, you must
 either specify <samp>-Wextra -Wunused</samp> (note that <samp>-Wall</samp> implies
 <samp>-Wunused</samp>), or separately specify <samp>-Wunused-parameter</samp>.
 </p>
 </dd>
 <dt><code>-Wuninitialized</code></dt>
 <dd><a name="index-Wuninitialized"></a>
 <a name="index-Wno_002duninitialized"></a>
 <p>Warn if an automatic variable is used without first being initialized
 or if a variable may be clobbered by a <code>setjmp</code> call. In C++,
 warn if a non-static reference or non-static &lsquo;<samp>const</samp>&rsquo; member
 appears in a class without constructors.
 </p>
 <p>If you want to warn about code that uses the uninitialized value of the
 variable in its own initializer, use the <samp>-Winit-self</samp> option.
 </p>
 <p>These warnings occur for individual uninitialized or clobbered
 elements of structure, union or array variables as well as for
 variables that are uninitialized or clobbered as a whole.  They do
 not occur for variables or elements declared <code>volatile</code>.  Because
 these warnings depend on optimization, the exact variables or elements
 for which there are warnings depends on the precise optimization
 options and version of GCC used.
 </p>
 <p>Note that there may be no warning about a variable that is used only
 to compute a value that itself is never used, because such
 computations may be deleted by data flow analysis before the warnings
 are printed.
 </p>
 </dd>
 <dt><code>-Wmaybe-uninitialized</code></dt>
 <dd><a name="index-Wmaybe_002duninitialized"></a>
 <a name="index-Wno_002dmaybe_002duninitialized"></a>
 <p>For an automatic variable, if there exists a path from the function
 entry to a use of the variable that is initialized, but there exist
 some other paths for which the variable is not initialized, the compiler
 emits a warning if it cannot prove the uninitialized paths are not
 executed at run time. These warnings are made optional because GCC is
 not smart enough to see all the reasons why the code might be correct
 in spite of appearing to have an error.  Here is one example of how
 this can happen:
 </p>
 <div class="smallexample">
 <pre class="smallexample">{
   int x;
   switch (y)
     {
     case 1: x = 1;
       break;
     case 2: x = 4;
       break;
     case 3: x = 5;
     }
   foo (x);
 }
 </pre></div>

 <p>If the value of <code>y</code> is always 1, 2 or 3, then <code>x</code> is
 always initialized, but GCC doesn&rsquo;t know this. To suppress the
 warning, you need to provide a default case with assert(0) or
 similar code.
 </p>
 <a name="index-longjmp-warnings"></a>
 <p>This option also warns when a non-volatile automatic variable might be
 changed by a call to <code>longjmp</code>.  These warnings as well are possible
 only in optimizing compilation.
 </p>
 <p>The compiler sees only the calls to <code>setjmp</code>.  It cannot know
 where <code>longjmp</code> will be called; in fact, a signal handler could
 call it at any point in the code.  As a result, you may get a warning
 even when there is in fact no problem because <code>longjmp</code> cannot
 in fact be called at the place that would cause a problem.
 </p>
 <p>Some spurious warnings can be avoided if you declare all the functions
 you use that never return as <code>noreturn</code>.  See <a href="Function-Attributes.html#Function-Attributes">Function Attributes</a>.
 </p>
 <p>This warning is enabled by <samp>-Wall</samp> or <samp>-Wextra</samp>.
 </p>
 </dd>
 <dt><code>-Wunknown-pragmas</code></dt>
 <dd><a name="index-Wunknown_002dpragmas"></a>
 <a name="index-Wno_002dunknown_002dpragmas"></a>
 <a name="index-warning-for-unknown-pragmas"></a>
 <a name="index-unknown-pragmas_002c-warning"></a>
 <a name="index-pragmas_002c-warning-of-unknown"></a>
 <p>Warn when a <code>#pragma</code> directive is encountered that is not understood by
 GCC.  If this command-line option is used, warnings are even issued
 for unknown pragmas in system header files.  This is not the case if
 the warnings are only enabled by the <samp>-Wall</samp> command-line option.
 </p>
 </dd>
 <dt><code>-Wno-pragmas</code></dt>
 <dd><a name="index-Wno_002dpragmas"></a>
 <a name="index-Wpragmas"></a>
 <p>Do not warn about misuses of pragmas, such as incorrect parameters,
 invalid syntax, or conflicts between pragmas.  See also
 <samp>-Wunknown-pragmas</samp>.
 </p>
 </dd>
 <dt><code>-Wstrict-aliasing</code></dt>
 <dd><a name="index-Wstrict_002daliasing"></a>
 <a name="index-Wno_002dstrict_002daliasing"></a>
 <p>This option is only active when <samp>-fstrict-aliasing</samp> is active.
 It warns about code that might break the strict aliasing rules that the
 compiler is using for optimization.  The warning does not catch all
 cases, but does attempt to catch the more common pitfalls.  It is
 included in <samp>-Wall</samp>.
 It is equivalent to <samp>-Wstrict-aliasing=3</samp>
 </p>
 </dd>
 <dt><code>-Wstrict-aliasing=n</code></dt>
 <dd><a name="index-Wstrict_002daliasing_003dn"></a>
 <p>This option is only active when <samp>-fstrict-aliasing</samp> is active.
 It warns about code that might break the strict aliasing rules that the
 compiler is using for optimization.
 Higher levels correspond to higher accuracy (fewer false positives).
 Higher levels also correspond to more effort, similar to the way <samp>-O</samp>
 works.
 <samp>-Wstrict-aliasing</samp> is equivalent to <samp>-Wstrict-aliasing=3</samp>.
 </p>
 <p>Level 1: Most aggressive, quick, least accurate.
 Possibly useful when higher levels
 do not warn but <samp>-fstrict-aliasing</samp> still breaks the code, as it has very few
 false negatives.  However, it has many false positives.
 Warns for all pointer conversions between possibly incompatible types,
 even if never dereferenced.  Runs in the front end only.
 </p>
 <p>Level 2: Aggressive, quick, not too precise.
 May still have many false positives (not as many as level 1 though),
 and few false negatives (but possibly more than level 1).
 Unlike level 1, it only warns when an address is taken.  Warns about
 incomplete types.  Runs in the front end only.
 </p>
 <p>Level 3 (default for <samp>-Wstrict-aliasing</samp>):
 Should have very few false positives and few false
 negatives.  Slightly slower than levels 1 or 2 when optimization is enabled.
 Takes care of the common pun+dereference pattern in the front end:
 <code>*(int*)&amp;some_float</code>.
 If optimization is enabled, it also runs in the back end, where it deals
 with multiple statement cases using flow-sensitive points-to information.
 Only warns when the converted pointer is dereferenced.
 Does not warn about incomplete types.
 </p>
 </dd>
 <dt><code>-Wstrict-overflow</code></dt>
 <dt><code>-Wstrict-overflow=<var>n</var></code></dt>
 <dd><a name="index-Wstrict_002doverflow"></a>
 <a name="index-Wno_002dstrict_002doverflow"></a>
 <p>This option is only active when <samp>-fstrict-overflow</samp> is active.
 It warns about cases where the compiler optimizes based on the
 assumption that signed overflow does not occur.  Note that it does not
 warn about all cases where the code might overflow: it only warns
 about cases where the compiler implements some optimization.  Thus
 this warning depends on the optimization level.
 </p>
 <p>An optimization that assumes that signed overflow does not occur is
 perfectly safe if the values of the variables involved are such that
 overflow never does, in fact, occur.  Therefore this warning can
 easily give a false positive: a warning about code that is not
 actually a problem.  To help focus on important issues, several
 warning levels are defined.  No warnings are issued for the use of
 undefined signed overflow when estimating how many iterations a loop
 requires, in particular when determining whether a loop will be
 executed at all.
 </p>
 <dl compact="compact">
 <dt><code>-Wstrict-overflow=1</code></dt>
 <dd><p>Warn about cases that are both questionable and easy to avoid.  For
 example,  with <samp>-fstrict-overflow</samp>, the compiler simplifies
 <code>x + 1 &gt; x</code> to <code>1</code>.  This level of
 <samp>-Wstrict-overflow</samp> is enabled by <samp>-Wall</samp>; higher levels
 are not, and must be explicitly requested.
 </p>
 </dd>
 <dt><code>-Wstrict-overflow=2</code></dt>
 <dd><p>Also warn about other cases where a comparison is simplified to a
 constant.  For example: <code>abs (x) &gt;= 0</code>.  This can only be
 simplified when <samp>-fstrict-overflow</samp> is in effect, because
 <code>abs (INT_MIN)</code> overflows to <code>INT_MIN</code>, which is less than
 zero.  <samp>-Wstrict-overflow</samp> (with no level) is the same as
 <samp>-Wstrict-overflow=2</samp>.
 </p>
 </dd>
 <dt><code>-Wstrict-overflow=3</code></dt>
 <dd><p>Also warn about other cases where a comparison is simplified.  For
 example: <code>x + 1 &gt; 1</code> is simplified to <code>x &gt; 0</code>.
 </p>
 </dd>
 <dt><code>-Wstrict-overflow=4</code></dt>
 <dd><p>Also warn about other simplifications not covered by the above cases.
 For example: <code>(x * 10) / 5</code> is simplified to <code>x * 2</code>.
 </p>
 </dd>
 <dt><code>-Wstrict-overflow=5</code></dt>
 <dd><p>Also warn about cases where the compiler reduces the magnitude of a
 constant involved in a comparison.  For example: <code>x + 2 &gt; y</code> is
 simplified to <code>x + 1 &gt;= y</code>.  This is reported only at the
 highest warning level because this simplification applies to many
 comparisons, so this warning level gives a very large number of
 false positives.
 </p></dd>
 </dl>

 </dd>
 <dt><code>-Wsuggest-attribute=<span class="roman">[</span>pure<span class="roman">|</span>const<span class="roman">|</span>noreturn<span class="roman">|</span>format<span class="roman">]</span></code></dt>
 <dd><a name="index-Wsuggest_002dattribute_003d"></a>
 <a name="index-Wno_002dsuggest_002dattribute_003d"></a>
 <p>Warn for cases where adding an attribute may be beneficial. The
 attributes currently supported are listed below.
 </p>
 <dl compact="compact">
 <dt><code>-Wsuggest-attribute=pure</code></dt>
 <dt><code>-Wsuggest-attribute=const</code></dt>
 <dt><code>-Wsuggest-attribute=noreturn</code></dt>
 <dd><a name="index-Wsuggest_002dattribute_003dpure"></a>
 <a name="index-Wno_002dsuggest_002dattribute_003dpure"></a>
 <a name="index-Wsuggest_002dattribute_003dconst"></a>
 <a name="index-Wno_002dsuggest_002dattribute_003dconst"></a>
 <a name="index-Wsuggest_002dattribute_003dnoreturn"></a>
 <a name="index-Wno_002dsuggest_002dattribute_003dnoreturn"></a>

 <p>Warn about functions that might be candidates for attributes
 <code>pure</code>, <code>const</code> or <code>noreturn</code>.  The compiler only warns for
 functions visible in other compilation units or (in the case of <code>pure</code> and
 <code>const</code>) if it cannot prove that the function returns normally. A function
 returns normally if it doesn&rsquo;t contain an infinite loop or return abnormally
 by throwing, calling <code>abort()</code> or trapping.  This analysis requires option
 <samp>-fipa-pure-const</samp>, which is enabled by default at <samp>-O</samp> and
 higher.  Higher optimization levels improve the accuracy of the analysis.
 </p>
 </dd>
 <dt><code>-Wsuggest-attribute=format</code></dt>
 <dt><code>-Wmissing-format-attribute</code></dt>
 <dd><a name="index-Wsuggest_002dattribute_003dformat"></a>
 <a name="index-Wmissing_002dformat_002dattribute"></a>
 <a name="index-Wno_002dsuggest_002dattribute_003dformat"></a>
 <a name="index-Wno_002dmissing_002dformat_002dattribute"></a>
 <a name="index-Wformat-2"></a>
 <a name="index-Wno_002dformat-1"></a>

 <p>Warn about function pointers that might be candidates for <code>format</code>
 attributes.  Note these are only possible candidates, not absolute ones.
 GCC guesses that function pointers with <code>format</code> attributes that
 are used in assignment, initialization, parameter passing or return
 statements should have a corresponding <code>format</code> attribute in the
 resulting type.  I.e. the left-hand side of the assignment or
 initialization, the type of the parameter variable, or the return type
 of the containing function respectively should also have a <code>format</code>
 attribute to avoid the warning.
 </p>
 <p>GCC also warns about function definitions that might be
 candidates for <code>format</code> attributes.  Again, these are only
 possible candidates.  GCC guesses that <code>format</code> attributes
 might be appropriate for any function that calls a function like
 <code>vprintf</code> or <code>vscanf</code>, but this might not always be the
 case, and some functions for which <code>format</code> attributes are
 appropriate may not be detected.
 </p></dd>
 </dl>

 </dd>
 <dt><code>-Warray-bounds</code></dt>
 <dd><a name="index-Wno_002darray_002dbounds"></a>
 <a name="index-Warray_002dbounds"></a>
 <p>This option is only active when <samp>-ftree-vrp</samp> is active
 (default for <samp>-O2</samp> and above). It warns about subscripts to arrays
 that are always out of bounds. This warning is enabled by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wno-div-by-zero</code></dt>
 <dd><a name="index-Wno_002ddiv_002dby_002dzero"></a>
 <a name="index-Wdiv_002dby_002dzero"></a>
 <p>Do not warn about compile-time integer division by zero.  Floating-point
 division by zero is not warned about, as it can be a legitimate way of
 obtaining infinities and NaNs.
 </p>
 </dd>
 <dt><code>-Wsystem-headers</code></dt>
 <dd><a name="index-Wsystem_002dheaders"></a>
 <a name="index-Wno_002dsystem_002dheaders"></a>
 <a name="index-warnings-from-system-headers"></a>
 <a name="index-system-headers_002c-warnings-from"></a>
 <p>Print warning messages for constructs found in system header files.
 Warnings from system headers are normally suppressed, on the assumption
 that they usually do not indicate real problems and would only make the
 compiler output harder to read.  Using this command-line option tells
 GCC to emit warnings from system headers as if they occurred in user
 code.  However, note that using <samp>-Wall</samp> in conjunction with this
 option does <em>not</em> warn about unknown pragmas in system
 headers&mdash;for that, <samp>-Wunknown-pragmas</samp> must also be used.
 </p>
 </dd>
 <dt><code>-Wtrampolines</code></dt>
 <dd><a name="index-Wtrampolines"></a>
 <a name="index-Wno_002dtrampolines"></a>
 <p>Warn about trampolines generated for pointers to nested functions.
 </p>
 <p>A trampoline is a small piece of data or code that is created at run
  time on the stack when the address of a nested function is taken, and
  is used to call the nested function indirectly.  For some targets, it
  is made up of data only and thus requires no special treatment.  But,
  for most targets, it is made up of code and thus requires the stack
  to be made executable in order for the program to work properly.
 </p>
 </dd>
 <dt><code>-Wfloat-equal</code></dt>
 <dd><a name="index-Wfloat_002dequal"></a>
 <a name="index-Wno_002dfloat_002dequal"></a>
 <p>Warn if floating-point values are used in equality comparisons.
 </p>
 <p>The idea behind this is that sometimes it is convenient (for the
 programmer) to consider floating-point values as approximations to
 infinitely precise real numbers.  If you are doing this, then you need
 to compute (by analyzing the code, or in some other way) the maximum or
 likely maximum error that the computation introduces, and allow for it
 when performing comparisons (and when producing output, but that&rsquo;s a
 different problem).  In particular, instead of testing for equality, you
 should check to see whether the two values have ranges that overlap; and
 this is done with the relational operators, so equality comparisons are
 probably mistaken.
 </p>
 </dd>
 <dt><code>-Wtraditional <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Wtraditional"></a>
 <a name="index-Wno_002dtraditional"></a>
 <p>Warn about certain constructs that behave differently in traditional and
 ISO C.  Also warn about ISO C constructs that have no traditional C
 equivalent, and/or problematic constructs that should be avoided.
 </p>
 <ul>
 <li> Macro parameters that appear within string literals in the macro body.
 In traditional C macro replacement takes place within string literals,
 but in ISO C it does not.

 </li><li> In traditional C, some preprocessor directives did not exist.
 Traditional preprocessors only considered a line to be a directive
 if the &lsquo;<samp>#</samp>&rsquo; appeared in column 1 on the line.  Therefore
 <samp>-Wtraditional</samp> warns about directives that traditional C
 understands but ignores because the &lsquo;<samp>#</samp>&rsquo; does not appear as the
 first character on the line.  It also suggests you hide directives like
 &lsquo;<samp>#pragma</samp>&rsquo; not understood by traditional C by indenting them.  Some
 traditional implementations do not recognize &lsquo;<samp>#elif</samp>&rsquo;, so this option
 suggests avoiding it altogether.

 </li><li> A function-like macro that appears without arguments.

 </li><li> The unary plus operator.

 </li><li> The &lsquo;<samp>U</samp>&rsquo; integer constant suffix, or the &lsquo;<samp>F</samp>&rsquo; or &lsquo;<samp>L</samp>&rsquo; floating-point
 constant suffixes.  (Traditional C does support the &lsquo;<samp>L</samp>&rsquo; suffix on integer
 constants.)  Note, these suffixes appear in macros defined in the system
 headers of most modern systems, e.g. the &lsquo;<samp>_MIN</samp>&rsquo;/&lsquo;<samp>_MAX</samp>&rsquo; macros in <code>&lt;limits.h&gt;</code>.
 Use of these macros in user code might normally lead to spurious
 warnings, however GCC&rsquo;s integrated preprocessor has enough context to
 avoid warning in these cases.

 </li><li> A function declared external in one block and then used after the end of
 the block.

 </li><li> A <code>switch</code> statement has an operand of type <code>long</code>.

 </li><li> A non-<code>static</code> function declaration follows a <code>static</code> one.
 This construct is not accepted by some traditional C compilers.

 </li><li> The ISO type of an integer constant has a different width or
 signedness from its traditional type.  This warning is only issued if
 the base of the constant is ten.  I.e. hexadecimal or octal values, which
 typically represent bit patterns, are not warned about.

 </li><li> Usage of ISO string concatenation is detected.

 </li><li> Initialization of automatic aggregates.

 </li><li> Identifier conflicts with labels.  Traditional C lacks a separate
 namespace for labels.

 </li><li> Initialization of unions.  If the initializer is zero, the warning is
 omitted.  This is done under the assumption that the zero initializer in
 user code appears conditioned on e.g. <code>__STDC__</code> to avoid missing
 initializer warnings and relies on default initialization to zero in the
 traditional C case.

 </li><li> Conversions by prototypes between fixed/floating-point values and vice
 versa.  The absence of these prototypes when compiling with traditional
 C causes serious problems.  This is a subset of the possible
 conversion warnings; for the full set use <samp>-Wtraditional-conversion</samp>.

 </li><li> Use of ISO C style function definitions.  This warning intentionally is
 <em>not</em> issued for prototype declarations or variadic functions
 because these ISO C features appear in your code when using
 libiberty&rsquo;s traditional C compatibility macros, <code>PARAMS</code> and
 <code>VPARAMS</code>.  This warning is also bypassed for nested functions
 because that feature is already a GCC extension and thus not relevant to
 traditional C compatibility.
 </li></ul>

 </dd>
 <dt><code>-Wtraditional-conversion <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Wtraditional_002dconversion"></a>
 <a name="index-Wno_002dtraditional_002dconversion"></a>
 <p>Warn if a prototype causes a type conversion that is different from what
 would happen to the same argument in the absence of a prototype.  This
 includes conversions of fixed point to floating and vice versa, and
 conversions changing the width or signedness of a fixed-point argument
 except when the same as the default promotion.
 </p>
 </dd>
 <dt><code>-Wdeclaration-after-statement <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Wdeclaration_002dafter_002dstatement"></a>
 <a name="index-Wno_002ddeclaration_002dafter_002dstatement"></a>
 <p>Warn when a declaration is found after a statement in a block.  This
 construct, known from C++, was introduced with ISO C99 and is by default
 allowed in GCC.  It is not supported by ISO C90 and was not supported by
 GCC versions before GCC 3.0.  See <a href="Mixed-Declarations.html#Mixed-Declarations">Mixed Declarations</a>.
 </p>
 </dd>
 <dt><code>-Wundef</code></dt>
 <dd><a name="index-Wundef"></a>
 <a name="index-Wno_002dundef"></a>
 <p>Warn if an undefined identifier is evaluated in an &lsquo;<samp>#if</samp>&rsquo; directive.
 </p>
 </dd>
 <dt><code>-Wno-endif-labels</code></dt>
 <dd><a name="index-Wno_002dendif_002dlabels"></a>
 <a name="index-Wendif_002dlabels"></a>
 <p>Do not warn whenever an &lsquo;<samp>#else</samp>&rsquo; or an &lsquo;<samp>#endif</samp>&rsquo; are followed by text.
 </p>
 </dd>
 <dt><code>-Wshadow</code></dt>
 <dd><a name="index-Wshadow"></a>
 <a name="index-Wno_002dshadow"></a>
 <p>Warn whenever a local variable or type declaration shadows another variable,
 parameter, type, or class member (in C++), or whenever a built-in function
 is shadowed. Note that in C++, the compiler warns if a local variable
 shadows an explicit typedef, but not if it shadows a struct/class/enum.
 </p>
 </dd>
 <dt><code>-Wlarger-than=<var>len</var></code></dt>
 <dd><a name="index-Wlarger_002dthan_003dlen"></a>
 <a name="index-Wlarger_002dthan_002dlen"></a>
 <p>Warn whenever an object of larger than <var>len</var> bytes is defined.
 </p>
 </dd>
 <dt><code>-Wframe-larger-than=<var>len</var></code></dt>
 <dd><a name="index-Wframe_002dlarger_002dthan"></a>
 <p>Warn if the size of a function frame is larger than <var>len</var> bytes.
 The computation done to determine the stack frame size is approximate
 and not conservative.
 The actual requirements may be somewhat greater than <var>len</var>
 even if you do not get a warning.  In addition, any space allocated
 via <code>alloca</code>, variable-length arrays, or related constructs
 is not included by the compiler when determining
 whether or not to issue a warning.
 </p>
 </dd>
 <dt><code>-Wno-free-nonheap-object</code></dt>
 <dd><a name="index-Wno_002dfree_002dnonheap_002dobject"></a>
 <a name="index-Wfree_002dnonheap_002dobject"></a>
 <p>Do not warn when attempting to free an object that was not allocated
 on the heap.
 </p>
 </dd>
 <dt><code>-Wstack-usage=<var>len</var></code></dt>
 <dd><a name="index-Wstack_002dusage"></a>
 <p>Warn if the stack usage of a function might be larger than <var>len</var> bytes.
 The computation done to determine the stack usage is conservative.
 Any space allocated via <code>alloca</code>, variable-length arrays, or related
 constructs is included by the compiler when determining whether or not to
 issue a warning.
 </p>
 <p>The message is in keeping with the output of <samp>-fstack-usage</samp>.
 </p>
 <ul>
 <li> If the stack usage is fully static but exceeds the specified amount, it&rsquo;s:

 <div class="smallexample">
 <pre class="smallexample">  warning: stack usage is 1120 bytes
 </pre></div>
 </li><li> If the stack usage is (partly) dynamic but bounded, it&rsquo;s:

 <div class="smallexample">
 <pre class="smallexample">  warning: stack usage might be 1648 bytes
 </pre></div>
 </li><li> If the stack usage is (partly) dynamic and not bounded, it&rsquo;s:

 <div class="smallexample">
 <pre class="smallexample">  warning: stack usage might be unbounded
 </pre></div>
 </li></ul>

 </dd>
 <dt><code>-Wunsafe-loop-optimizations</code></dt>
 <dd><a name="index-Wunsafe_002dloop_002doptimizations"></a>
 <a name="index-Wno_002dunsafe_002dloop_002doptimizations"></a>
 <p>Warn if the loop cannot be optimized because the compiler cannot
 assume anything on the bounds of the loop indices.  With
 <samp>-funsafe-loop-optimizations</samp> warn if the compiler makes
 such assumptions.
 </p>
 </dd>
 <dt><code>-Wno-pedantic-ms-format <span class="roman">(MinGW targets only)</span></code></dt>
 <dd><a name="index-Wno_002dpedantic_002dms_002dformat"></a>
 <a name="index-Wpedantic_002dms_002dformat"></a>
 <p>When used in combination with <samp>-Wformat</samp>
 and <samp>-pedantic</samp> without GNU extensions, this option
 disables the warnings about non-ISO <code>printf</code> / <code>scanf</code> format
 width specifiers <code>I32</code>, <code>I64</code>, and <code>I</code> used on Windows targets,
 which depend on the MS runtime.
 </p>
 </dd>
 <dt><code>-Wpointer-arith</code></dt>
 <dd><a name="index-Wpointer_002darith"></a>
 <a name="index-Wno_002dpointer_002darith"></a>
 <p>Warn about anything that depends on the &ldquo;size of&rdquo; a function type or
 of <code>void</code>.  GNU C assigns these types a size of 1, for
 convenience in calculations with <code>void *</code> pointers and pointers
 to functions.  In C++, warn also when an arithmetic operation involves
 <code>NULL</code>.  This warning is also enabled by <samp>-Wpedantic</samp>.
 </p>
 </dd>
 <dt><code>-Wtype-limits</code></dt>
 <dd><a name="index-Wtype_002dlimits"></a>
 <a name="index-Wno_002dtype_002dlimits"></a>
 <p>Warn if a comparison is always true or always false due to the limited
 range of the data type, but do not warn for constant expressions.  For
 example, warn if an unsigned variable is compared against zero with
 &lsquo;<samp>&lt;</samp>&rsquo; or &lsquo;<samp>&gt;=</samp>&rsquo;.  This warning is also enabled by
 <samp>-Wextra</samp>.
 </p>
 </dd>
 <dt><code>-Wbad-function-cast <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Wbad_002dfunction_002dcast"></a>
 <a name="index-Wno_002dbad_002dfunction_002dcast"></a>
 <p>Warn whenever a function call is cast to a non-matching type.
 For example, warn if <code>int malloc()</code> is cast to <code>anything *</code>.
 </p>
 </dd>
 <dt><code>-Wc++-compat <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><p>Warn about ISO C constructs that are outside of the common subset of
 ISO C and ISO C++, e.g. request for implicit conversion from
 <code>void *</code> to a pointer to non-<code>void</code> type.
 </p>
 </dd>
 <dt><code>-Wc++11-compat <span class="roman">(C++ and Objective-C++ only)</span></code></dt>
 <dd><p>Warn about C++ constructs whose meaning differs between ISO C++ 1998
 and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are keywords
 in ISO C++ 2011.  This warning turns on <samp>-Wnarrowing</samp> and is
 enabled by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wcast-qual</code></dt>
 <dd><a name="index-Wcast_002dqual"></a>
 <a name="index-Wno_002dcast_002dqual"></a>
 <p>Warn whenever a pointer is cast so as to remove a type qualifier from
 the target type.  For example, warn if a <code>const char *</code> is cast
 to an ordinary <code>char *</code>.
 </p>
 <p>Also warn when making a cast that introduces a type qualifier in an
 unsafe way.  For example, casting <code>char **</code> to <code>const char **</code>
 is unsafe, as in this example:
 </p>
 <div class="smallexample">
 <pre class="smallexample">  /* p is char ** value.  */
   const char **q = (const char **) p;
   /* Assignment of readonly string to const char * is OK.  */
   *q = &quot;string&quot;;
   /* Now char** pointer points to read-only memory.  */
   **p = 'b';
 </pre></div>

 </dd>
 <dt><code>-Wcast-align</code></dt>
 <dd><a name="index-Wcast_002dalign"></a>
 <a name="index-Wno_002dcast_002dalign"></a>
 <p>Warn whenever a pointer is cast such that the required alignment of the
 target is increased.  For example, warn if a <code>char *</code> is cast to
 an <code>int *</code> on machines where integers can only be accessed at
 two- or four-byte boundaries.
 </p>
 </dd>
 <dt><code>-Wwrite-strings</code></dt>
 <dd><a name="index-Wwrite_002dstrings"></a>
 <a name="index-Wno_002dwrite_002dstrings"></a>
 <p>When compiling C, give string constants the type <code>const
 char[<var>length</var>]</code> so that copying the address of one into a
 non-<code>const</code> <code>char *</code> pointer produces a warning.  These
 warnings help you find at compile time code that can try to write
 into a string constant, but only if you have been very careful about
 using <code>const</code> in declarations and prototypes.  Otherwise, it is
 just a nuisance. This is why we did not make <samp>-Wall</samp> request
 these warnings.
 </p>
 <p>When compiling C++, warn about the deprecated conversion from string
 literals to <code>char *</code>.  This warning is enabled by default for C++
 programs.
 </p>
 </dd>
 <dt><code>-Wclobbered</code></dt>
 <dd><a name="index-Wclobbered"></a>
 <a name="index-Wno_002dclobbered"></a>
 <p>Warn for variables that might be changed by &lsquo;<samp>longjmp</samp>&rsquo; or
 &lsquo;<samp>vfork</samp>&rsquo;.  This warning is also enabled by <samp>-Wextra</samp>.
 </p>
 </dd>
 <dt><code>-Wconditionally-supported <span class="roman">(C++ and Objective-C++ only)</span></code></dt>
 <dd><a name="index-Wconditionally_002dsupported"></a>
 <a name="index-Wno_002dconditionally_002dsupported"></a>
 <p>Warn for conditionally-supported (C++11 [intro.defs]) constructs.
 </p>
 </dd>
 <dt><code>-Wconversion</code></dt>
 <dd><a name="index-Wconversion"></a>
 <a name="index-Wno_002dconversion"></a>
 <p>Warn for implicit conversions that may alter a value. This includes
 conversions between real and integer, like <code>abs (x)</code> when
 <code>x</code> is <code>double</code>; conversions between signed and unsigned,
 like <code>unsigned ui = -1</code>; and conversions to smaller types, like
 <code>sqrtf (M_PI)</code>. Do not warn for explicit casts like <code>abs
 ((int) x)</code> and <code>ui = (unsigned) -1</code>, or if the value is not
 changed by the conversion like in <code>abs (2.0)</code>.  Warnings about
 conversions between signed and unsigned integers can be disabled by
 using <samp>-Wno-sign-conversion</samp>.
 </p>
 <p>For C++, also warn for confusing overload resolution for user-defined
 conversions; and conversions that never use a type conversion
 operator: conversions to <code>void</code>, the same type, a base class or a
 reference to them. Warnings about conversions between signed and
 unsigned integers are disabled by default in C++ unless
 <samp>-Wsign-conversion</samp> is explicitly enabled.
 </p>
 </dd>
 <dt><code>-Wno-conversion-null <span class="roman">(C++ and Objective-C++ only)</span></code></dt>
 <dd><a name="index-Wconversion_002dnull"></a>
 <a name="index-Wno_002dconversion_002dnull"></a>
 <p>Do not warn for conversions between <code>NULL</code> and non-pointer
 types. <samp>-Wconversion-null</samp> is enabled by default.
 </p>
 </dd>
 <dt><code>-Wzero-as-null-pointer-constant <span class="roman">(C++ and Objective-C++ only)</span></code></dt>
 <dd><a name="index-Wzero_002das_002dnull_002dpointer_002dconstant"></a>
 <a name="index-Wno_002dzero_002das_002dnull_002dpointer_002dconstant"></a>
 <p>Warn when a literal &rsquo;0&rsquo; is used as null pointer constant.  This can
 be useful to facilitate the conversion to <code>nullptr</code> in C++11.
 </p>
 </dd>
 <dt><code>-Wdate-time</code></dt>
 <dd><a name="index-Wdate_002dtime"></a>
 <a name="index-Wno_002ddate_002dtime"></a>
 <p>Warn when macros <code>__TIME__</code>, <code>__DATE__</code> or <code>__TIMESTAMP__</code>
 are encountered as they might prevent bit-wise-identical reproducible
 compilations.
 </p>
 </dd>
 <dt><code>-Wdelete-incomplete <span class="roman">(C++ and Objective-C++ only)</span></code></dt>
 <dd><a name="index-Wdelete_002dincomplete"></a>
 <a name="index-Wno_002ddelete_002dincomplete"></a>
 <p>Warn when deleting a pointer to incomplete type, which may cause
 undefined behavior at runtime.  This warning is enabled by default.
 </p>
 </dd>
 <dt><code>-Wuseless-cast <span class="roman">(C++ and Objective-C++ only)</span></code></dt>
 <dd><a name="index-Wuseless_002dcast"></a>
 <a name="index-Wno_002duseless_002dcast"></a>
 <p>Warn when an expression is casted to its own type.
 </p>
 </dd>
 <dt><code>-Wempty-body</code></dt>
 <dd><a name="index-Wempty_002dbody"></a>
 <a name="index-Wno_002dempty_002dbody"></a>
 <p>Warn if an empty body occurs in an &lsquo;<samp>if</samp>&rsquo;, &lsquo;<samp>else</samp>&rsquo; or &lsquo;<samp>do
 while</samp>&rsquo; statement.  This warning is also enabled by <samp>-Wextra</samp>.
 </p>
 </dd>
 <dt><code>-Wenum-compare</code></dt>
 <dd><a name="index-Wenum_002dcompare"></a>
 <a name="index-Wno_002denum_002dcompare"></a>
 <p>Warn about a comparison between values of different enumerated types.
 In C++ enumeral mismatches in conditional expressions are also
 diagnosed and the warning is enabled by default.  In C this warning is
 enabled by <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wjump-misses-init <span class="roman">(C, Objective-C only)</span></code></dt>
 <dd><a name="index-Wjump_002dmisses_002dinit"></a>
 <a name="index-Wno_002djump_002dmisses_002dinit"></a>
 <p>Warn if a <code>goto</code> statement or a <code>switch</code> statement jumps
 forward across the initialization of a variable, or jumps backward to a
 label after the variable has been initialized.  This only warns about
 variables that are initialized when they are declared.  This warning is
 only supported for C and Objective-C; in C++ this sort of branch is an
 error in any case.
 </p>
 <p><samp>-Wjump-misses-init</samp> is included in <samp>-Wc++-compat</samp>.  It
 can be disabled with the <samp>-Wno-jump-misses-init</samp> option.
 </p>
 </dd>
 <dt><code>-Wsign-compare</code></dt>
 <dd><a name="index-Wsign_002dcompare"></a>
 <a name="index-Wno_002dsign_002dcompare"></a>
 <a name="index-warning-for-comparison-of-signed-and-unsigned-values"></a>
 <a name="index-comparison-of-signed-and-unsigned-values_002c-warning"></a>
 <a name="index-signed-and-unsigned-values_002c-comparison-warning"></a>
 <p>Warn when a comparison between signed and unsigned values could produce
 an incorrect result when the signed value is converted to unsigned.
 This warning is also enabled by <samp>-Wextra</samp>; to get the other warnings
 of <samp>-Wextra</samp> without this warning, use <samp>-Wextra -Wno-sign-compare</samp>.
 </p>
 </dd>
 <dt><code>-Wsign-conversion</code></dt>
 <dd><a name="index-Wsign_002dconversion"></a>
 <a name="index-Wno_002dsign_002dconversion"></a>
 <p>Warn for implicit conversions that may change the sign of an integer
 value, like assigning a signed integer expression to an unsigned
 integer variable. An explicit cast silences the warning. In C, this
 option is enabled also by <samp>-Wconversion</samp>.
 </p>
 </dd>
 <dt><code>-Wfloat-conversion</code></dt>
 <dd><a name="index-Wfloat_002dconversion"></a>
 <a name="index-Wno_002dfloat_002dconversion"></a>
 <p>Warn for implicit conversions that reduce the precision of a real value.
 This includes conversions from real to integer, and from higher precision
 real to lower precision real values.  This option is also enabled by
 <samp>-Wconversion</samp>.
 </p>
 </dd>
 <dt><code>-Wsizeof-pointer-memaccess</code></dt>
 <dd><a name="index-Wsizeof_002dpointer_002dmemaccess"></a>
 <a name="index-Wno_002dsizeof_002dpointer_002dmemaccess"></a>
 <p>Warn for suspicious length parameters to certain string and memory built-in
 functions if the argument uses <code>sizeof</code>.  This warning warns e.g.
 about <code>memset (ptr, 0, sizeof (ptr));</code> if <code>ptr</code> is not an array,
 but a pointer, and suggests a possible fix, or about
 <code>memcpy (&amp;foo, ptr, sizeof (&amp;foo));</code>.  This warning is enabled by
 <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Waddress</code></dt>
 <dd><a name="index-Waddress"></a>
 <a name="index-Wno_002daddress"></a>
 <p>Warn about suspicious uses of memory addresses. These include using
 the address of a function in a conditional expression, such as
 <code>void func(void); if (func)</code>, and comparisons against the memory
 address of a string literal, such as <code>if (x == &quot;abc&quot;)</code>.  Such
 uses typically indicate a programmer error: the address of a function
 always evaluates to true, so their use in a conditional usually
 indicate that the programmer forgot the parentheses in a function
 call; and comparisons against string literals result in unspecified
 behavior and are not portable in C, so they usually indicate that the
 programmer intended to use <code>strcmp</code>.  This warning is enabled by
 <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wlogical-op</code></dt>
 <dd><a name="index-Wlogical_002dop"></a>
 <a name="index-Wno_002dlogical_002dop"></a>
 <p>Warn about suspicious uses of logical operators in expressions.
 This includes using logical operators in contexts where a
 bit-wise operator is likely to be expected.
 </p>
 </dd>
 <dt><code>-Waggregate-return</code></dt>
 <dd><a name="index-Waggregate_002dreturn"></a>
 <a name="index-Wno_002daggregate_002dreturn"></a>
 <p>Warn if any functions that return structures or unions are defined or
 called.  (In languages where you can return an array, this also elicits
 a warning.)
 </p>
 </dd>
 <dt><code>-Wno-aggressive-loop-optimizations</code></dt>
 <dd><a name="index-Wno_002daggressive_002dloop_002doptimizations"></a>
 <a name="index-Waggressive_002dloop_002doptimizations"></a>
 <p>Warn if in a loop with constant number of iterations the compiler detects
 undefined behavior in some statement during one or more of the iterations.
 </p>
 </dd>
 <dt><code>-Wno-attributes</code></dt>
 <dd><a name="index-Wno_002dattributes"></a>
 <a name="index-Wattributes"></a>
 <p>Do not warn if an unexpected <code>__attribute__</code> is used, such as
 unrecognized attributes, function attributes applied to variables,
 etc.  This does not stop errors for incorrect use of supported
 attributes.
 </p>
 </dd>
 <dt><code>-Wno-builtin-macro-redefined</code></dt>
 <dd><a name="index-Wno_002dbuiltin_002dmacro_002dredefined"></a>
 <a name="index-Wbuiltin_002dmacro_002dredefined"></a>
 <p>Do not warn if certain built-in macros are redefined.  This suppresses
 warnings for redefinition of <code>__TIMESTAMP__</code>, <code>__TIME__</code>,
 <code>__DATE__</code>, <code>__FILE__</code>, and <code>__BASE_FILE__</code>.
 </p>
 </dd>
 <dt><code>-Wstrict-prototypes <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Wstrict_002dprototypes"></a>
 <a name="index-Wno_002dstrict_002dprototypes"></a>
 <p>Warn if a function is declared or defined without specifying the
 argument types.  (An old-style function definition is permitted without
 a warning if preceded by a declaration that specifies the argument
 types.)
 </p>
 </dd>
 <dt><code>-Wold-style-declaration <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Wold_002dstyle_002ddeclaration"></a>
 <a name="index-Wno_002dold_002dstyle_002ddeclaration"></a>
 <p>Warn for obsolescent usages, according to the C Standard, in a
 declaration. For example, warn if storage-class specifiers like
 <code>static</code> are not the first things in a declaration.  This warning
 is also enabled by <samp>-Wextra</samp>.
 </p>
 </dd>
 <dt><code>-Wold-style-definition <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Wold_002dstyle_002ddefinition"></a>
 <a name="index-Wno_002dold_002dstyle_002ddefinition"></a>
 <p>Warn if an old-style function definition is used.  A warning is given
 even if there is a previous prototype.
 </p>
 </dd>
 <dt><code>-Wmissing-parameter-type <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Wmissing_002dparameter_002dtype"></a>
 <a name="index-Wno_002dmissing_002dparameter_002dtype"></a>
 <p>A function parameter is declared without a type specifier in K&amp;R-style
 functions:
 </p>
 <div class="smallexample">
 <pre class="smallexample">void foo(bar) { }
 </pre></div>

 <p>This warning is also enabled by <samp>-Wextra</samp>.
 </p>
 </dd>
 <dt><code>-Wmissing-prototypes <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Wmissing_002dprototypes"></a>
 <a name="index-Wno_002dmissing_002dprototypes"></a>
 <p>Warn if a global function is defined without a previous prototype
 declaration.  This warning is issued even if the definition itself
 provides a prototype.  Use this option to detect global functions
 that do not have a matching prototype declaration in a header file.
 This option is not valid for C++ because all function declarations
 provide prototypes and a non-matching declaration will declare an
 overload rather than conflict with an earlier declaration.
 Use <samp>-Wmissing-declarations</samp> to detect missing declarations in C++.
 </p>
 </dd>
 <dt><code>-Wmissing-declarations</code></dt>
 <dd><a name="index-Wmissing_002ddeclarations"></a>
 <a name="index-Wno_002dmissing_002ddeclarations"></a>
 <p>Warn if a global function is defined without a previous declaration.
 Do so even if the definition itself provides a prototype.
 Use this option to detect global functions that are not declared in
 header files.  In C, no warnings are issued for functions with previous
 non-prototype declarations; use <samp>-Wmissing-prototype</samp> to detect
 missing prototypes.  In C++, no warnings are issued for function templates,
 or for inline functions, or for functions in anonymous namespaces.
 </p>
 </dd>
 <dt><code>-Wmissing-field-initializers</code></dt>
 <dd><a name="index-Wmissing_002dfield_002dinitializers"></a>
 <a name="index-Wno_002dmissing_002dfield_002dinitializers"></a>
 <a name="index-W-1"></a>
 <a name="index-Wextra-1"></a>
 <a name="index-Wno_002dextra-1"></a>
 <p>Warn if a structure&rsquo;s initializer has some fields missing.  For
 example, the following code causes such a warning, because
 <code>x.h</code> is implicitly zero:
 </p>
 <div class="smallexample">
 <pre class="smallexample">struct s { int f, g, h; };
 struct s x = { 3, 4 };
 </pre></div>

 <p>This option does not warn about designated initializers, so the following
 modification does not trigger a warning:
 </p>
 <div class="smallexample">
 <pre class="smallexample">struct s { int f, g, h; };
 struct s x = { .f = 3, .g = 4 };
 </pre></div>

 <p>This warning is included in <samp>-Wextra</samp>.  To get other <samp>-Wextra</samp>
 warnings without this one, use <samp>-Wextra -Wno-missing-field-initializers</samp>.
 </p>
 </dd>
 <dt><code>-Wno-multichar</code></dt>
 <dd><a name="index-Wno_002dmultichar"></a>
 <a name="index-Wmultichar"></a>
 <p>Do not warn if a multicharacter constant (&lsquo;<samp>'FOOF'</samp>&rsquo;) is used.
 Usually they indicate a typo in the user&rsquo;s code, as they have
 implementation-defined values, and should not be used in portable code.
 </p>
 </dd>
 <dt><code>-Wnormalized=&lt;none|id|nfc|nfkc&gt;</code></dt>
 <dd><a name="index-Wnormalized_003d"></a>
 <a name="index-NFC"></a>
 <a name="index-NFKC"></a>
 <a name="index-character-set_002c-input-normalization"></a>
 <p>In ISO C and ISO C++, two identifiers are different if they are
 different sequences of characters.  However, sometimes when characters
 outside the basic ASCII character set are used, you can have two
 different character sequences that look the same.  To avoid confusion,
 the ISO 10646 standard sets out some <em>normalization rules</em> which
 when applied ensure that two sequences that look the same are turned into
 the same sequence.  GCC can warn you if you are using identifiers that
 have not been normalized; this option controls that warning.
 </p>
 <p>There are four levels of warning supported by GCC.  The default is
 <samp>-Wnormalized=nfc</samp>, which warns about any identifier that is
 not in the ISO 10646 &ldquo;C&rdquo; normalized form, <em>NFC</em>.  NFC is the
 recommended form for most uses.
 </p>
 <p>Unfortunately, there are some characters allowed in identifiers by
 ISO C and ISO C++ that, when turned into NFC, are not allowed in
 identifiers.  That is, there&rsquo;s no way to use these symbols in portable
 ISO C or C++ and have all your identifiers in NFC.
 <samp>-Wnormalized=id</samp> suppresses the warning for these characters.
 It is hoped that future versions of the standards involved will correct
 this, which is why this option is not the default.
 </p>
 <p>You can switch the warning off for all characters by writing
 <samp>-Wnormalized=none</samp>.  You should only do this if you
 are using some other normalization scheme (like &ldquo;D&rdquo;), because
 otherwise you can easily create bugs that are literally impossible to see.
 </p>
 <p>Some characters in ISO 10646 have distinct meanings but look identical
 in some fonts or display methodologies, especially once formatting has
 been applied.  For instance <code>\u207F</code>, &ldquo;SUPERSCRIPT LATIN SMALL
 LETTER N&rdquo;, displays just like a regular <code>n</code> that has been
 placed in a superscript.  ISO 10646 defines the <em>NFKC</em>
 normalization scheme to convert all these into a standard form as
 well, and GCC warns if your code is not in NFKC if you use
 <samp>-Wnormalized=nfkc</samp>.  This warning is comparable to warning
 about every identifier that contains the letter O because it might be
 confused with the digit 0, and so is not the default, but may be
 useful as a local coding convention if the programming environment
 cannot be fixed to display these characters distinctly.
 </p>
 </dd>
 <dt><code>-Wno-deprecated</code></dt>
 <dd><a name="index-Wno_002ddeprecated"></a>
 <a name="index-Wdeprecated"></a>
 <p>Do not warn about usage of deprecated features.  See <a href="Deprecated-Features.html#Deprecated-Features">Deprecated Features</a>.
 </p>
 </dd>
 <dt><code>-Wno-deprecated-declarations</code></dt>
 <dd><a name="index-Wno_002ddeprecated_002ddeclarations"></a>
 <a name="index-Wdeprecated_002ddeclarations"></a>
 <p>Do not warn about uses of functions (see <a href="Function-Attributes.html#Function-Attributes">Function Attributes</a>),
 variables (see <a href="Variable-Attributes.html#Variable-Attributes">Variable Attributes</a>), and types (see <a href="Type-Attributes.html#Type-Attributes">Type Attributes</a>) marked as deprecated by using the <code>deprecated</code>
 attribute.
 </p>
 </dd>
 <dt><code>-Wno-overflow</code></dt>
 <dd><a name="index-Wno_002doverflow"></a>
 <a name="index-Woverflow"></a>
 <p>Do not warn about compile-time overflow in constant expressions.
 </p>
 </dd>
 <dt><code>-Wopenmp-simd</code></dt>
 <dd><a name="index-Wopenm_002dsimd"></a>
 <p>Warn if the vectorizer cost model overrides the OpenMP or the Cilk Plus
 simd directive set by user.  The <samp>-fsimd-cost-model=unlimited</samp> can
 be used to relax the cost model.
 </p>
 </dd>
 <dt><code>-Woverride-init <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Woverride_002dinit"></a>
 <a name="index-Wno_002doverride_002dinit"></a>
 <a name="index-W-2"></a>
 <a name="index-Wextra-2"></a>
 <a name="index-Wno_002dextra-2"></a>
 <p>Warn if an initialized field without side effects is overridden when
 using designated initializers (see <a href="Designated-Inits.html#Designated-Inits">Designated
 Initializers</a>).
 </p>
 <p>This warning is included in <samp>-Wextra</samp>.  To get other
 <samp>-Wextra</samp> warnings without this one, use <samp>-Wextra
 -Wno-override-init</samp>.
 </p>
 </dd>
 <dt><code>-Wpacked</code></dt>
 <dd><a name="index-Wpacked"></a>
 <a name="index-Wno_002dpacked"></a>
 <p>Warn if a structure is given the packed attribute, but the packed
 attribute has no effect on the layout or size of the structure.
 Such structures may be mis-aligned for little benefit.  For
 instance, in this code, the variable <code>f.x</code> in <code>struct bar</code>
 is misaligned even though <code>struct bar</code> does not itself
 have the packed attribute:
 </p>
 <div class="smallexample">
 <pre class="smallexample">struct foo {
   int x;
   char a, b, c, d;
 } __attribute__((packed));
 struct bar {
   char z;
   struct foo f;
 };
 </pre></div>

 </dd>
 <dt><code>-Wpacked-bitfield-compat</code></dt>
 <dd><a name="index-Wpacked_002dbitfield_002dcompat"></a>
 <a name="index-Wno_002dpacked_002dbitfield_002dcompat"></a>
 <p>The 4.1, 4.2 and 4.3 series of GCC ignore the <code>packed</code> attribute
 on bit-fields of type <code>char</code>.  This has been fixed in GCC 4.4 but
 the change can lead to differences in the structure layout.  GCC
 informs you when the offset of such a field has changed in GCC 4.4.
 For example there is no longer a 4-bit padding between field <code>a</code>
 and <code>b</code> in this structure:
 </p>
 <div class="smallexample">
 <pre class="smallexample">struct foo
 {
   char a:4;
   char b:8;
 } __attribute__ ((packed));
 </pre></div>

 <p>This warning is enabled by default.  Use
 <samp>-Wno-packed-bitfield-compat</samp> to disable this warning.
 </p>
 </dd>
 <dt><code>-Wpadded</code></dt>
 <dd><a name="index-Wpadded"></a>
 <a name="index-Wno_002dpadded"></a>
 <p>Warn if padding is included in a structure, either to align an element
 of the structure or to align the whole structure.  Sometimes when this
 happens it is possible to rearrange the fields of the structure to
 reduce the padding and so make the structure smaller.
 </p>
 </dd>
 <dt><code>-Wredundant-decls</code></dt>
 <dd><a name="index-Wredundant_002ddecls"></a>
 <a name="index-Wno_002dredundant_002ddecls"></a>
 <p>Warn if anything is declared more than once in the same scope, even in
 cases where multiple declaration is valid and changes nothing.
 </p>
 </dd>
 <dt><code>-Wnested-externs <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Wnested_002dexterns"></a>
 <a name="index-Wno_002dnested_002dexterns"></a>
 <p>Warn if an <code>extern</code> declaration is encountered within a function.
 </p>
 </dd>
 <dt><code>-Wno-inherited-variadic-ctor</code></dt>
 <dd><a name="index-Winherited_002dvariadic_002dctor"></a>
 <a name="index-Wno_002dinherited_002dvariadic_002dctor"></a>
 <p>Suppress warnings about use of C++11 inheriting constructors when the
 base class inherited from has a C variadic constructor; the warning is
 on by default because the ellipsis is not inherited.
 </p>
 </dd>
 <dt><code>-Winline</code></dt>
 <dd><a name="index-Winline"></a>
 <a name="index-Wno_002dinline"></a>
 <p>Warn if a function that is declared as inline cannot be inlined.
 Even with this option, the compiler does not warn about failures to
 inline functions declared in system headers.
 </p>
 <p>The compiler uses a variety of heuristics to determine whether or not
 to inline a function.  For example, the compiler takes into account
 the size of the function being inlined and the amount of inlining
 that has already been done in the current function.  Therefore,
 seemingly insignificant changes in the source program can cause the
 warnings produced by <samp>-Winline</samp> to appear or disappear.
 </p>
 </dd>
 <dt><code>-Wno-invalid-offsetof <span class="roman">(C++ and Objective-C++ only)</span></code></dt>
 <dd><a name="index-Wno_002dinvalid_002doffsetof"></a>
 <a name="index-Winvalid_002doffsetof"></a>
 <p>Suppress warnings from applying the &lsquo;<samp>offsetof</samp>&rsquo; macro to a non-POD
 type.  According to the 1998 ISO C++ standard, applying &lsquo;<samp>offsetof</samp>&rsquo;
 to a non-POD type is undefined.  In existing C++ implementations,
 however, &lsquo;<samp>offsetof</samp>&rsquo; typically gives meaningful results even when
 applied to certain kinds of non-POD types (such as a simple
 &lsquo;<samp>struct</samp>&rsquo; that fails to be a POD type only by virtue of having a
 constructor).  This flag is for users who are aware that they are
 writing nonportable code and who have deliberately chosen to ignore the
 warning about it.
 </p>
 <p>The restrictions on &lsquo;<samp>offsetof</samp>&rsquo; may be relaxed in a future version
 of the C++ standard.
 </p>
 </dd>
 <dt><code>-Wno-int-to-pointer-cast</code></dt>
 <dd><a name="index-Wno_002dint_002dto_002dpointer_002dcast"></a>
 <a name="index-Wint_002dto_002dpointer_002dcast"></a>
 <p>Suppress warnings from casts to pointer type of an integer of a
 different size. In C++, casting to a pointer type of smaller size is
 an error. <samp>Wint-to-pointer-cast</samp> is enabled by default.
 </p>

 </dd>
 <dt><code>-Wno-pointer-to-int-cast <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Wno_002dpointer_002dto_002dint_002dcast"></a>
 <a name="index-Wpointer_002dto_002dint_002dcast"></a>
 <p>Suppress warnings from casts from a pointer to an integer type of a
 different size.
 </p>
 </dd>
 <dt><code>-Winvalid-pch</code></dt>
 <dd><a name="index-Winvalid_002dpch"></a>
 <a name="index-Wno_002dinvalid_002dpch"></a>
 <p>Warn if a precompiled header (see <a href="Precompiled-Headers.html#Precompiled-Headers">Precompiled Headers</a>) is found in
 the search path but can&rsquo;t be used.
 </p>
 </dd>
 <dt><code>-Wlong-long</code></dt>
 <dd><a name="index-Wlong_002dlong"></a>
 <a name="index-Wno_002dlong_002dlong"></a>
 <p>Warn if &lsquo;<samp>long long</samp>&rsquo; type is used.  This is enabled by either
 <samp>-Wpedantic</samp> or <samp>-Wtraditional</samp> in ISO C90 and C++98
 modes.  To inhibit the warning messages, use <samp>-Wno-long-long</samp>.
 </p>
 </dd>
 <dt><code>-Wvariadic-macros</code></dt>
 <dd><a name="index-Wvariadic_002dmacros"></a>
 <a name="index-Wno_002dvariadic_002dmacros"></a>
 <p>Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
 alternate syntax when in pedantic ISO C99 mode.  This is default.
 To inhibit the warning messages, use <samp>-Wno-variadic-macros</samp>.
 </p>
 </dd>
 <dt><code>-Wvarargs</code></dt>
 <dd><a name="index-Wvarargs"></a>
 <a name="index-Wno_002dvarargs"></a>
 <p>Warn upon questionable usage of the macros used to handle variable
 arguments like &lsquo;<samp>va_start</samp>&rsquo;.  This is default.  To inhibit the
 warning messages, use <samp>-Wno-varargs</samp>.
 </p>
 </dd>
 <dt><code>-Wvector-operation-performance</code></dt>
 <dd><a name="index-Wvector_002doperation_002dperformance"></a>
 <a name="index-Wno_002dvector_002doperation_002dperformance"></a>
 <p>Warn if vector operation is not implemented via SIMD capabilities of the
 architecture.  Mainly useful for the performance tuning.
 Vector operation can be implemented <code>piecewise</code>, which means that the
 scalar operation is performed on every vector element;
 <code>in parallel</code>, which means that the vector operation is implemented
 using scalars of wider type, which normally is more performance efficient;
 and <code>as a single scalar</code>, which means that vector fits into a
 scalar type.
 </p>
 </dd>
 <dt><code>-Wno-virtual-move-assign</code></dt>
 <dd><a name="index-Wvirtual_002dmove_002dassign"></a>
 <a name="index-Wno_002dvirtual_002dmove_002dassign"></a>
 <p>Suppress warnings about inheriting from a virtual base with a
 non-trivial C++11 move assignment operator.  This is dangerous because
 if the virtual base is reachable along more than one path, it will be
 moved multiple times, which can mean both objects end up in the
 moved-from state.  If the move assignment operator is written to avoid
 moving from a moved-from object, this warning can be disabled.
 </p>
 </dd>
 <dt><code>-Wvla</code></dt>
 <dd><a name="index-Wvla"></a>
 <a name="index-Wno_002dvla"></a>
 <p>Warn if variable length array is used in the code.
 <samp>-Wno-vla</samp> prevents the <samp>-Wpedantic</samp> warning of
 the variable length array.
 </p>
 </dd>
 <dt><code>-Wvolatile-register-var</code></dt>
 <dd><a name="index-Wvolatile_002dregister_002dvar"></a>
 <a name="index-Wno_002dvolatile_002dregister_002dvar"></a>
 <p>Warn if a register variable is declared volatile.  The volatile
 modifier does not inhibit all optimizations that may eliminate reads
 and/or writes to register variables.  This warning is enabled by
 <samp>-Wall</samp>.
 </p>
 </dd>
 <dt><code>-Wdisabled-optimization</code></dt>
 <dd><a name="index-Wdisabled_002doptimization"></a>
 <a name="index-Wno_002ddisabled_002doptimization"></a>
 <p>Warn if a requested optimization pass is disabled.  This warning does
 not generally indicate that there is anything wrong with your code; it
 merely indicates that GCC&rsquo;s optimizers are unable to handle the code
 effectively.  Often, the problem is that your code is too big or too
 complex; GCC refuses to optimize programs when the optimization
 itself is likely to take inordinate amounts of time.
 </p>
 </dd>
 <dt><code>-Wpointer-sign <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Wpointer_002dsign"></a>
 <a name="index-Wno_002dpointer_002dsign"></a>
 <p>Warn for pointer argument passing or assignment with different signedness.
 This option is only supported for C and Objective-C.  It is implied by
 <samp>-Wall</samp> and by <samp>-Wpedantic</samp>, which can be disabled with
 <samp>-Wno-pointer-sign</samp>.
 </p>
 </dd>
 <dt><code>-Wstack-protector</code></dt>
 <dd><a name="index-Wstack_002dprotector"></a>
 <a name="index-Wno_002dstack_002dprotector"></a>
 <p>This option is only active when <samp>-fstack-protector</samp> is active.  It
 warns about functions that are not protected against stack smashing.
 </p>
 </dd>
 <dt><code>-Woverlength-strings</code></dt>
 <dd><a name="index-Woverlength_002dstrings"></a>
 <a name="index-Wno_002doverlength_002dstrings"></a>
 <p>Warn about string constants that are longer than the &ldquo;minimum
 maximum&rdquo; length specified in the C standard.  Modern compilers
 generally allow string constants that are much longer than the
 standard&rsquo;s minimum limit, but very portable programs should avoid
 using longer strings.
 </p>
 <p>The limit applies <em>after</em> string constant concatenation, and does
 not count the trailing NUL.  In C90, the limit was 509 characters; in
 C99, it was raised to 4095.  C++98 does not specify a normative
 minimum maximum, so we do not diagnose overlength strings in C++.
 </p>
 <p>This option is implied by <samp>-Wpedantic</samp>, and can be disabled with
 <samp>-Wno-overlength-strings</samp>.
 </p>
 </dd>
 <dt><code>-Wunsuffixed-float-constants <span class="roman">(C and Objective-C only)</span></code></dt>
 <dd><a name="index-Wunsuffixed_002dfloat_002dconstants"></a>

 <p>Issue a warning for any floating constant that does not have
 a suffix.  When used together with <samp>-Wsystem-headers</samp> it
 warns about such constants in system header files.  This can be useful
 when preparing code to use with the <code>FLOAT_CONST_DECIMAL64</code> pragma
 from the decimal floating-point extension to C99.
 </p></dd>
 </dl>

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