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| <title>The GNU Fortran Compiler: Error and Warning Options</title> |
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| <a name="Error-and-Warning-Options"></a> |
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| <p> |
| Next: <a href="Debugging-Options.html#Debugging-Options" accesskey="n" rel="next">Debugging Options</a>, Previous: <a href="Preprocessing-Options.html#Preprocessing-Options" accesskey="p" rel="prev">Preprocessing Options</a>, Up: <a href="Invoking-GNU-Fortran.html#Invoking-GNU-Fortran" accesskey="u" rel="up">Invoking GNU Fortran</a> [<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-errors-and-warnings"></a> |
| <h3 class="section">2.4 Options to request or suppress errors and warnings</h3> |
| <a name="index-options_002c-warnings"></a> |
| <a name="index-options_002c-errors"></a> |
| <a name="index-warnings_002c-suppressing"></a> |
| <a name="index-messages_002c-error"></a> |
| <a name="index-messages_002c-warning"></a> |
| <a name="index-suppressing-warnings"></a> |
| |
| <p>Errors are diagnostic messages that report that the GNU Fortran compiler |
| cannot compile the relevant piece of source code. The compiler will |
| continue to process the program in an attempt to report further errors |
| to aid in debugging, but will not produce any compiled output. |
| </p> |
| <p>Warnings are diagnostic messages that report constructions which |
| are not inherently erroneous but which are risky or suggest there is |
| likely to be a bug in the program. Unless <samp>-Werror</samp> is specified, |
| they do not prevent compilation of the program. |
| </p> |
| <p>You can request many specific warnings with options beginning <samp>-W</samp>, |
| for example <samp>-Wimplicit</samp> to request warnings on implicit |
| declarations. Each of these specific warning options also has a |
| negative form beginning <samp>-Wno-</samp> to turn off warnings; |
| for example, <samp>-Wno-implicit</samp>. This manual lists only one of the |
| two forms, whichever is not the default. |
| </p> |
| <p>These options control the amount and kinds of errors and warnings produced |
| by GNU Fortran: |
| </p> |
| <dl compact="compact"> |
| <dt><code>-fmax-errors=<var>n</var></code></dt> |
| <dd><a name="index-fmax_002derrors_003dn"></a> |
| <a name="index-errors_002c-limiting"></a> |
| <p>Limits the maximum number of error messages to <var>n</var>, at which point |
| GNU Fortran bails out rather than attempting to continue processing the |
| source code. If <var>n</var> is 0, there is no limit on the number of error |
| messages produced. |
| </p> |
| </dd> |
| <dt><code>-fsyntax-only</code></dt> |
| <dd><a name="index-fsyntax_002donly"></a> |
| <a name="index-syntax-checking"></a> |
| <p>Check the code for syntax errors, but do not actually compile it. This |
| will generate module files for each module present in the code, but no |
| other output file. |
| </p> |
| </dd> |
| <dt><code>-pedantic</code></dt> |
| <dd><a name="index-pedantic"></a> |
| <p>Issue warnings for uses of extensions to Fortran 95. |
| <samp>-pedantic</samp> also applies to C-language constructs where they |
| occur in GNU Fortran source files, such as use of ‘<samp>\e</samp>’ in a |
| character constant within a directive like <code>#include</code>. |
| </p> |
| <p>Valid Fortran 95 programs should compile properly with or without |
| this option. |
| However, without this option, certain GNU extensions and traditional |
| Fortran features are supported as well. |
| With this option, many of them are rejected. |
| </p> |
| <p>Some users try to use <samp>-pedantic</samp> to check programs for conformance. |
| They soon find that it does not do quite what they want—it finds some |
| nonstandard practices, but not all. |
| However, improvements to GNU Fortran in this area are welcome. |
| </p> |
| <p>This should be used in conjunction with <samp>-std=f95</samp>, |
| <samp>-std=f2003</samp> or <samp>-std=f2008</samp>. |
| </p> |
| </dd> |
| <dt><code>-pedantic-errors</code></dt> |
| <dd><a name="index-pedantic_002derrors"></a> |
| <p>Like <samp>-pedantic</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-all-warnings"></a> |
| <a name="index-warnings_002c-all"></a> |
| <p>Enables commonly used warning options pertaining to usage that |
| we recommend avoiding and that we believe are easy to avoid. |
| This currently includes <samp>-Waliasing</samp>, <samp>-Wampersand</samp>, |
| <samp>-Wconversion</samp>, <samp>-Wsurprising</samp>, <samp>-Wc-binding-type</samp>, |
| <samp>-Wintrinsics-std</samp>, <samp>-Wno-tabs</samp>, <samp>-Wintrinsic-shadow</samp>, |
| <samp>-Wline-truncation</samp>, <samp>-Wtarget-lifetime</samp>, |
| <samp>-Wreal-q-constant</samp> and <samp>-Wunused</samp>. |
| </p> |
| </dd> |
| <dt><code>-Waliasing</code></dt> |
| <dd><a name="index-Waliasing"></a> |
| <a name="index-aliasing"></a> |
| <a name="index-warnings_002c-aliasing"></a> |
| <p>Warn about possible aliasing of dummy arguments. Specifically, it warns |
| if the same actual argument is associated with a dummy argument with |
| <code>INTENT(IN)</code> and a dummy argument with <code>INTENT(OUT)</code> in a call |
| with an explicit interface. |
| </p> |
| <p>The following example will trigger the warning. |
| </p><div class="smallexample"> |
| <pre class="smallexample"> interface |
| subroutine bar(a,b) |
| integer, intent(in) :: a |
| integer, intent(out) :: b |
| end subroutine |
| end interface |
| integer :: a |
| |
| call bar(a,a) |
| </pre></div> |
| |
| </dd> |
| <dt><code>-Wampersand</code></dt> |
| <dd><a name="index-Wampersand"></a> |
| <a name="index-warnings_002c-ampersand"></a> |
| <a name="index-_0026"></a> |
| <p>Warn about missing ampersand in continued character constants. The warning is |
| given with <samp>-Wampersand</samp>, <samp>-pedantic</samp>, <samp>-std=f95</samp>, |
| <samp>-std=f2003</samp> and <samp>-std=f2008</samp>. Note: With no ampersand |
| given in a continued character constant, GNU Fortran assumes continuation |
| at the first non-comment, non-whitespace character after the ampersand |
| that initiated the continuation. |
| </p> |
| </dd> |
| <dt><code>-Warray-temporaries</code></dt> |
| <dd><a name="index-Warray_002dtemporaries"></a> |
| <a name="index-warnings_002c-array-temporaries"></a> |
| <p>Warn about array temporaries generated by the compiler. The information |
| generated by this warning is sometimes useful in optimization, in order to |
| avoid such temporaries. |
| </p> |
| </dd> |
| <dt><code>-Wc-binding-type</code></dt> |
| <dd><a name="index-Wc_002dbinding_002dtype"></a> |
| <a name="index-warning_002c-C-binding-type"></a> |
| <p>Warn if the a variable might not be C interoperable. In particular, warn if |
| the variable has been declared using an intrinsic type with default kind |
| instead of using a kind parameter defined for C interoperability in the |
| intrinsic <code>ISO_C_Binding</code> module. This option is implied by |
| <samp>-Wall</samp>. |
| </p> |
| </dd> |
| <dt><code>-Wcharacter-truncation</code></dt> |
| <dd><a name="index-Wcharacter_002dtruncation"></a> |
| <a name="index-warnings_002c-character-truncation"></a> |
| <p>Warn when a character assignment will truncate the assigned string. |
| </p> |
| </dd> |
| <dt><code>-Wline-truncation</code></dt> |
| <dd><a name="index-Wline_002dtruncation"></a> |
| <a name="index-warnings_002c-line-truncation"></a> |
| <p>Warn when a source code line will be truncated. This option is |
| implied by <samp>-Wall</samp>. |
| </p> |
| </dd> |
| <dt><code>-Wconversion</code></dt> |
| <dd><a name="index-Wconversion"></a> |
| <a name="index-warnings_002c-conversion"></a> |
| <a name="index-conversion"></a> |
| <p>Warn about implicit conversions that are likely to change the value of |
| the expression after conversion. Implied by <samp>-Wall</samp>. |
| </p> |
| </dd> |
| <dt><code>-Wconversion-extra</code></dt> |
| <dd><a name="index-Wconversion_002dextra"></a> |
| <a name="index-warnings_002c-conversion-1"></a> |
| <a name="index-conversion-1"></a> |
| <p>Warn about implicit conversions between different types and kinds. |
| </p> |
| </dd> |
| <dt><code>-Wextra</code></dt> |
| <dd><a name="index-Wextra"></a> |
| <a name="index-extra-warnings"></a> |
| <a name="index-warnings_002c-extra"></a> |
| <p>Enables some warning options for usages of language features which |
| may be problematic. This currently includes <samp>-Wcompare-reals</samp> |
| and <samp>-Wunused-parameter</samp>. |
| </p> |
| </dd> |
| <dt><code>-Wimplicit-interface</code></dt> |
| <dd><a name="index-Wimplicit_002dinterface"></a> |
| <a name="index-warnings_002c-implicit-interface"></a> |
| <p>Warn if a procedure is called without an explicit interface. |
| Note this only checks that an explicit interface is present. It does not |
| check that the declared interfaces are consistent across program units. |
| </p> |
| </dd> |
| <dt><code>-Wimplicit-procedure</code></dt> |
| <dd><a name="index-Wimplicit_002dprocedure"></a> |
| <a name="index-warnings_002c-implicit-procedure"></a> |
| <p>Warn if a procedure is called that has neither an explicit interface |
| nor has been declared as <code>EXTERNAL</code>. |
| </p> |
| </dd> |
| <dt><code>-Wintrinsics-std</code></dt> |
| <dd><a name="index-Wintrinsics_002dstd"></a> |
| <a name="index-warnings_002c-non_002dstandard-intrinsics"></a> |
| <a name="index-warnings_002c-intrinsics-of-other-standards"></a> |
| <p>Warn if <code>gfortran</code> finds a procedure named like an intrinsic not |
| available in the currently selected standard (with <samp>-std</samp>) and treats |
| it as <code>EXTERNAL</code> procedure because of this. <samp>-fall-intrinsics</samp> can |
| be used to never trigger this behavior and always link to the intrinsic |
| regardless of the selected standard. |
| </p> |
| </dd> |
| <dt><code>-Wreal-q-constant</code></dt> |
| <dd><a name="index-Wreal_002dq_002dconstant"></a> |
| <a name="index-warnings_002c-q-exponent_002dletter"></a> |
| <p>Produce a warning if a real-literal-constant contains a <code>q</code> |
| exponent-letter. |
| </p> |
| </dd> |
| <dt><code>-Wsurprising</code></dt> |
| <dd><a name="index-Wsurprising"></a> |
| <a name="index-warnings_002c-suspicious-code"></a> |
| <p>Produce a warning when “suspicious” code constructs are encountered. |
| While technically legal these usually indicate that an error has been made. |
| </p> |
| <p>This currently produces a warning under the following circumstances: |
| </p> |
| <ul> |
| <li> An INTEGER SELECT construct has a CASE that can never be matched as its |
| lower value is greater than its upper value. |
| |
| </li><li> A LOGICAL SELECT construct has three CASE statements. |
| |
| </li><li> A TRANSFER specifies a source that is shorter than the destination. |
| |
| </li><li> The type of a function result is declared more than once with the same type. If |
| <samp>-pedantic</samp> or standard-conforming mode is enabled, this is an error. |
| |
| </li><li> A <code>CHARACTER</code> variable is declared with negative length. |
| </li></ul> |
| |
| </dd> |
| <dt><code>-Wtabs</code></dt> |
| <dd><a name="index-Wtabs"></a> |
| <a name="index-warnings_002c-tabs"></a> |
| <a name="index-tabulators"></a> |
| <p>By default, tabs are accepted as whitespace, but tabs are not members |
| of the Fortran Character Set. For continuation lines, a tab followed |
| by a digit between 1 and 9 is supported. <samp>-Wno-tabs</samp> will cause |
| a warning to be issued if a tab is encountered. Note, <samp>-Wno-tabs</samp> |
| is active for <samp>-pedantic</samp>, <samp>-std=f95</samp>, <samp>-std=f2003</samp>, |
| <samp>-std=f2008</samp> and <samp>-Wall</samp>. |
| </p> |
| </dd> |
| <dt><code>-Wunderflow</code></dt> |
| <dd><a name="index-Wunderflow"></a> |
| <a name="index-warnings_002c-underflow"></a> |
| <a name="index-underflow"></a> |
| <p>Produce a warning when numerical constant expressions are |
| encountered, which yield an UNDERFLOW during compilation. |
| </p> |
| </dd> |
| <dt><code>-Wintrinsic-shadow</code></dt> |
| <dd><a name="index-Wintrinsic_002dshadow"></a> |
| <a name="index-warnings_002c-intrinsic"></a> |
| <a name="index-intrinsic"></a> |
| <p>Warn if a user-defined procedure or module procedure has the same name as an |
| intrinsic; in this case, an explicit interface or <code>EXTERNAL</code> or |
| <code>INTRINSIC</code> declaration might be needed to get calls later resolved to |
| the desired intrinsic/procedure. This option is implied by <samp>-Wall</samp>. |
| </p> |
| </dd> |
| <dt><code>-Wunused-dummy-argument</code></dt> |
| <dd><a name="index-Wunused_002ddummy_002dargument"></a> |
| <a name="index-warnings_002c-unused-dummy-argument"></a> |
| <a name="index-unused-dummy-argument"></a> |
| <a name="index-dummy-argument_002c-unused"></a> |
| <p>Warn about unused dummy arguments. This option is implied by <samp>-Wall</samp>. |
| </p> |
| </dd> |
| <dt><code>-Wunused-parameter</code></dt> |
| <dd><a name="index-Wunused_002dparameter"></a> |
| <a name="index-warnings_002c-unused-parameter"></a> |
| <a name="index-unused-parameter"></a> |
| <p>Contrary to <code>gcc</code>’s meaning of <samp>-Wunused-parameter</samp>, |
| <code>gfortran</code>’s implementation of this option does not warn |
| about unused dummy arguments (see <samp>-Wunused-dummy-argument</samp>), |
| but about unused <code>PARAMETER</code> values. <samp>-Wunused-parameter</samp> |
| is not included in <samp>-Wall</samp> but is implied by <samp>-Wall -Wextra</samp>. |
| </p> |
| </dd> |
| <dt><code>-Walign-commons</code></dt> |
| <dd><a name="index-Walign_002dcommons"></a> |
| <a name="index-warnings_002c-alignment-of-COMMON-blocks"></a> |
| <a name="index-alignment-of-COMMON-blocks"></a> |
| <p>By default, <code>gfortran</code> warns about any occasion of variables being |
| padded for proper alignment inside a <code>COMMON</code> block. This warning can be turned |
| off via <samp>-Wno-align-commons</samp>. See also <samp>-falign-commons</samp>. |
| </p> |
| </dd> |
| <dt><code>-Wfunction-elimination</code></dt> |
| <dd><a name="index-Wfunction_002delimination"></a> |
| <a name="index-function-elimination"></a> |
| <a name="index-warnings_002c-function-elimination"></a> |
| <p>Warn if any calls to functions are eliminated by the optimizations |
| enabled by the <samp>-ffrontend-optimize</samp> option. |
| </p> |
| </dd> |
| <dt><code>-Wrealloc-lhs</code></dt> |
| <dd><a name="index-Wrealloc_002dlhs"></a> |
| <a name="index-Reallocate-the-LHS-in-assignments_002c-notification"></a> |
| <p>Warn when the compiler might insert code to for allocation or reallocation of |
| an allocatable array variable of intrinsic type in intrinsic assignments. In |
| hot loops, the Fortran 2003 reallocation feature may reduce the performance. |
| If the array is already allocated with the correct shape, consider using a |
| whole-array array-spec (e.g. <code>(:,:,:)</code>) for the variable on the left-hand |
| side to prevent the reallocation check. Note that in some cases the warning |
| is shown, even if the compiler will optimize reallocation checks away. For |
| instance, when the right-hand side contains the same variable multiplied by |
| a scalar. See also <samp>-frealloc-lhs</samp>. |
| </p> |
| </dd> |
| <dt><code>-Wrealloc-lhs-all</code></dt> |
| <dd><a name="index-Wrealloc_002dlhs_002dall"></a> |
| <p>Warn when the compiler inserts code to for allocation or reallocation of an |
| allocatable variable; this includes scalars and derived types. |
| </p> |
| </dd> |
| <dt><code>-Wcompare-reals</code></dt> |
| <dd><a name="index-Wcompare_002dreals"></a> |
| <p>Warn when comparing real or complex types for equality or inequality. |
| This option is implied by <samp>-Wextra</samp>. |
| </p> |
| </dd> |
| <dt><code>-Wtarget-lifetime</code></dt> |
| <dd><a name="index-Wtargt_002dlifetime"></a> |
| <p>Warn if the pointer in a pointer assignment might be longer than the its |
| target. This option is implied by <samp>-Wall</samp>. |
| </p> |
| </dd> |
| <dt><code>-Wzerotrip</code></dt> |
| <dd><a name="index-Wzerotrip"></a> |
| <p>Warn if a <code>DO</code> loop is known to execute zero times at compile |
| time. This option is implied by <samp>-Wall</samp>. |
| </p> |
| </dd> |
| <dt><code>-Werror</code></dt> |
| <dd><a name="index-Werror"></a> |
| <a name="index-warnings_002c-to-errors"></a> |
| <p>Turns all warnings into errors. |
| </p></dd> |
| </dl> |
| |
| <p>See <a href="http://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#Warning-Options">Options to Request or Suppress Errors and |
| Warnings</a> in <cite>Using the GNU Compiler Collection (GCC)</cite>, for information on |
| more options offered by the GBE shared by <code>gfortran</code>, <code>gcc</code> |
| and other GNU compilers. |
| </p> |
| <p>Some of these have no effect when compiling programs written in Fortran. |
| </p> |
| <hr> |
| <div class="header"> |
| <p> |
| Next: <a href="Debugging-Options.html#Debugging-Options" accesskey="n" rel="next">Debugging Options</a>, Previous: <a href="Preprocessing-Options.html#Preprocessing-Options" accesskey="p" rel="prev">Preprocessing Options</a>, Up: <a href="Invoking-GNU-Fortran.html#Invoking-GNU-Fortran" accesskey="u" rel="up">Invoking GNU Fortran</a> [<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> |
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