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| <title>The GNU Fortran Compiler: Fortran Dialect Options</title> |
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| <a name="Fortran-Dialect-Options"></a> |
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| Next: <a href="Preprocessing-Options.html#Preprocessing-Options" accesskey="n" rel="next">Preprocessing Options</a>, Previous: <a href="Option-Summary.html#Option-Summary" accesskey="p" rel="prev">Option Summary</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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| <hr> |
| <a name="Options-controlling-Fortran-dialect"></a> |
| <h3 class="section">2.2 Options controlling Fortran dialect</h3> |
| <a name="index-dialect-options"></a> |
| <a name="index-language_002c-dialect-options"></a> |
| <a name="index-options_002c-dialect"></a> |
| |
| <p>The following options control the details of the Fortran dialect |
| accepted by the compiler: |
| </p> |
| <dl compact="compact"> |
| <dt><code>-ffree-form</code></dt> |
| <dt><code>-ffixed-form</code></dt> |
| <dd><a name="index-ffree_002dform"></a> |
| <a name="index-fno_002dfixed_002dform"></a> |
| <a name="index-options_002c-Fortran-dialect"></a> |
| <a name="index-file-format_002c-free"></a> |
| <a name="index-file-format_002c-fixed"></a> |
| <p>Specify the layout used by the source file. The free form layout |
| was introduced in Fortran 90. Fixed form was traditionally used in |
| older Fortran programs. When neither option is specified, the source |
| form is determined by the file extension. |
| </p> |
| </dd> |
| <dt><code>-fall-intrinsics</code></dt> |
| <dd><a name="index-fall_002dintrinsics"></a> |
| <p>This option causes all intrinsic procedures (including the GNU-specific |
| extensions) to be accepted. This can be useful with <samp>-std=f95</samp> to |
| force standard-compliance but get access to the full range of intrinsics |
| available with <code>gfortran</code>. As a consequence, <samp>-Wintrinsics-std</samp> |
| will be ignored and no user-defined procedure with the same name as any |
| intrinsic will be called except when it is explicitly declared <code>EXTERNAL</code>. |
| </p> |
| </dd> |
| <dt><code>-fd-lines-as-code</code></dt> |
| <dt><code>-fd-lines-as-comments</code></dt> |
| <dd><a name="index-fd_002dlines_002das_002dcode"></a> |
| <a name="index-fd_002dlines_002das_002dcomments"></a> |
| <p>Enable special treatment for lines beginning with <code>d</code> or <code>D</code> |
| in fixed form sources. If the <samp>-fd-lines-as-code</samp> option is |
| given they are treated as if the first column contained a blank. If the |
| <samp>-fd-lines-as-comments</samp> option is given, they are treated as |
| comment lines. |
| </p> |
| </dd> |
| <dt><code>-fdollar-ok</code></dt> |
| <dd><a name="index-fdollar_002dok"></a> |
| <a name="index-_0024"></a> |
| <a name="index-symbol-names"></a> |
| <a name="index-character-set"></a> |
| <p>Allow ‘<samp>$</samp>’ as a valid non-first character in a symbol name. Symbols |
| that start with ‘<samp>$</samp>’ are rejected since it is unclear which rules to |
| apply to implicit typing as different vendors implement different rules. |
| Using ‘<samp>$</samp>’ in <code>IMPLICIT</code> statements is also rejected. |
| </p> |
| </dd> |
| <dt><code>-fbackslash</code></dt> |
| <dd><a name="index-backslash-1"></a> |
| <a name="index-backslash"></a> |
| <a name="index-escape-characters"></a> |
| <p>Change the interpretation of backslashes in string literals from a single |
| backslash character to “C-style” escape characters. The following |
| combinations are expanded <code>\a</code>, <code>\b</code>, <code>\f</code>, <code>\n</code>, |
| <code>\r</code>, <code>\t</code>, <code>\v</code>, <code>\\</code>, and <code>\0</code> to the ASCII |
| characters alert, backspace, form feed, newline, carriage return, |
| horizontal tab, vertical tab, backslash, and NUL, respectively. |
| Additionally, <code>\x</code><var>nn</var>, <code>\u</code><var>nnnn</var> and |
| <code>\U</code><var>nnnnnnnn</var> (where each <var>n</var> is a hexadecimal digit) are |
| translated into the Unicode characters corresponding to the specified code |
| points. All other combinations of a character preceded by \ are |
| unexpanded. |
| </p> |
| </dd> |
| <dt><code>-fmodule-private</code></dt> |
| <dd><a name="index-fmodule_002dprivate"></a> |
| <a name="index-module-entities"></a> |
| <a name="index-private"></a> |
| <p>Set the default accessibility of module entities to <code>PRIVATE</code>. |
| Use-associated entities will not be accessible unless they are explicitly |
| declared as <code>PUBLIC</code>. |
| </p> |
| </dd> |
| <dt><code>-ffixed-line-length-<var>n</var></code></dt> |
| <dd><a name="index-ffixed_002dline_002dlength_002dn"></a> |
| <a name="index-file-format_002c-fixed-1"></a> |
| <p>Set column after which characters are ignored in typical fixed-form |
| lines in the source file, and through which spaces are assumed (as |
| if padded to that length) after the ends of short fixed-form lines. |
| </p> |
| <p>Popular values for <var>n</var> include 72 (the |
| standard and the default), 80 (card image), and 132 (corresponding |
| to “extended-source” options in some popular compilers). |
| <var>n</var> may also be ‘<samp>none</samp>’, meaning that the entire line is meaningful |
| and that continued character constants never have implicit spaces appended |
| to them to fill out the line. |
| <samp>-ffixed-line-length-0</samp> means the same thing as |
| <samp>-ffixed-line-length-none</samp>. |
| </p> |
| </dd> |
| <dt><code>-ffree-line-length-<var>n</var></code></dt> |
| <dd><a name="index-ffree_002dline_002dlength_002dn"></a> |
| <a name="index-file-format_002c-free-1"></a> |
| <p>Set column after which characters are ignored in typical free-form |
| lines in the source file. The default value is 132. |
| <var>n</var> may be ‘<samp>none</samp>’, meaning that the entire line is meaningful. |
| <samp>-ffree-line-length-0</samp> means the same thing as |
| <samp>-ffree-line-length-none</samp>. |
| </p> |
| </dd> |
| <dt><code>-fmax-identifier-length=<var>n</var></code></dt> |
| <dd><a name="index-fmax_002didentifier_002dlength_003dn"></a> |
| <p>Specify the maximum allowed identifier length. Typical values are |
| 31 (Fortran 95) and 63 (Fortran 2003 and Fortran 2008). |
| </p> |
| </dd> |
| <dt><code>-fimplicit-none</code></dt> |
| <dd><a name="index-fimplicit_002dnone"></a> |
| <p>Specify that no implicit typing is allowed, unless overridden by explicit |
| <code>IMPLICIT</code> statements. This is the equivalent of adding |
| <code>implicit none</code> to the start of every procedure. |
| </p> |
| </dd> |
| <dt><code>-fcray-pointer</code></dt> |
| <dd><a name="index-fcray_002dpointer"></a> |
| <p>Enable the Cray pointer extension, which provides C-like pointer |
| functionality. |
| </p> |
| </dd> |
| <dt><code>-fopenmp</code></dt> |
| <dd><a name="index-fopenmp"></a> |
| <a name="index-OpenMP"></a> |
| <p>Enable the OpenMP extensions. This includes OpenMP <code>!$omp</code> directives |
| in free form |
| and <code>c$omp</code>, <code>*$omp</code> and <code>!$omp</code> directives in fixed form, |
| <code>!$</code> conditional compilation sentinels in free form |
| and <code>c$</code>, <code>*$</code> and <code>!$</code> sentinels in fixed form, |
| and when linking arranges for the OpenMP runtime library to be linked |
| in. The option <samp>-fopenmp</samp> implies <samp>-frecursive</samp>. |
| </p> |
| </dd> |
| <dt><code>-fno-range-check</code></dt> |
| <dd><a name="index-frange_002dcheck"></a> |
| <p>Disable range checking on results of simplification of constant |
| expressions during compilation. For example, GNU Fortran will give |
| an error at compile time when simplifying <code>a = 1. / 0</code>. |
| With this option, no error will be given and <code>a</code> will be assigned |
| the value <code>+Infinity</code>. If an expression evaluates to a value |
| outside of the relevant range of [<code>-HUGE()</code>:<code>HUGE()</code>], |
| then the expression will be replaced by <code>-Inf</code> or <code>+Inf</code> |
| as appropriate. |
| Similarly, <code>DATA i/Z'FFFFFFFF'/</code> will result in an integer overflow |
| on most systems, but with <samp>-fno-range-check</samp> the value will |
| “wrap around” and <code>i</code> will be initialized to <em>-1</em> instead. |
| </p> |
| </dd> |
| <dt><code>-fdefault-integer-8</code></dt> |
| <dd><a name="index-fdefault_002dinteger_002d8"></a> |
| <p>Set the default integer and logical types to an 8 byte wide type. This option |
| also affects the kind of integer constants like <code>42</code>. Unlike |
| <samp>-finteger-4-integer-8</samp>, it does not promote variables with explicit |
| kind declaration. |
| </p> |
| </dd> |
| <dt><code>-fdefault-real-8</code></dt> |
| <dd><a name="index-fdefault_002dreal_002d8"></a> |
| <p>Set the default real type to an 8 byte wide type. This option also affects |
| the kind of non-double real constants like <code>1.0</code>, and does promote |
| the default width of <code>DOUBLE PRECISION</code> to 16 bytes if possible, unless |
| <code>-fdefault-double-8</code> is given, too. Unlike <samp>-freal-4-real-8</samp>, |
| it does not promote variables with explicit kind declaration. |
| </p> |
| </dd> |
| <dt><code>-fdefault-double-8</code></dt> |
| <dd><a name="index-fdefault_002ddouble_002d8"></a> |
| <p>Set the <code>DOUBLE PRECISION</code> type to an 8 byte wide type. Do nothing if this |
| is already the default. If <samp>-fdefault-real-8</samp> is given, |
| <code>DOUBLE PRECISION</code> would instead be promoted to 16 bytes if possible, and |
| <samp>-fdefault-double-8</samp> can be used to prevent this. The kind of real |
| constants like <code>1.d0</code> will not be changed by <samp>-fdefault-real-8</samp> |
| though, so also <samp>-fdefault-double-8</samp> does not affect it. |
| </p> |
| </dd> |
| <dt><code>-finteger-4-integer-8</code></dt> |
| <dd><a name="index-finteger_002d4_002dinteger_002d8"></a> |
| <p>Promote all <code>INTEGER(KIND=4)</code> entities to an <code>INTEGER(KIND=8)</code> |
| entities. If <code>KIND=8</code> is unavailable, then an error will be issued. |
| This option should be used with care and may not be suitable for your codes. |
| Areas of possible concern include calls to external procedures, |
| alignment in <code>EQUIVALENCE</code> and/or <code>COMMON</code>, generic interfaces, |
| BOZ literal constant conversion, and I/O. Inspection of the intermediate |
| representation of the translated Fortran code, produced by |
| <samp>-fdump-tree-original</samp>, is suggested. |
| </p> |
| </dd> |
| <dt><code>-freal-4-real-8</code></dt> |
| <dt><code>-freal-4-real-10</code></dt> |
| <dt><code>-freal-4-real-16</code></dt> |
| <dt><code>-freal-8-real-4</code></dt> |
| <dt><code>-freal-8-real-10</code></dt> |
| <dt><code>-freal-8-real-16</code></dt> |
| <dd><a name="index-freal_002d4_002dreal_002d8"></a> |
| <a name="index-freal_002d4_002dreal_002d10"></a> |
| <a name="index-freal_002d4_002dreal_002d16"></a> |
| <a name="index-freal_002d8_002dreal_002d4"></a> |
| <a name="index-freal_002d8_002dreal_002d10"></a> |
| <a name="index-freal_002d8_002dreal_002d16"></a> |
| <a name="index-options_002c-real-kind-type-promotion"></a> |
| <p>Promote all <code>REAL(KIND=M)</code> entities to <code>REAL(KIND=N)</code> entities. |
| If <code>REAL(KIND=N)</code> is unavailable, then an error will be issued. |
| All other real kind types are unaffected by this option. |
| These options should be used with care and may not be suitable for your |
| codes. Areas of possible concern include calls to external procedures, |
| alignment in <code>EQUIVALENCE</code> and/or <code>COMMON</code>, generic interfaces, |
| BOZ literal constant conversion, and I/O. Inspection of the intermediate |
| representation of the translated Fortran code, produced by |
| <samp>-fdump-tree-original</samp>, is suggested. |
| </p> |
| </dd> |
| <dt><code>-std=<var>std</var></code></dt> |
| <dd><a name="index-std_003dstd-option"></a> |
| <p>Specify the standard to which the program is expected to conform, which |
| may be one of ‘<samp>f95</samp>’, ‘<samp>f2003</samp>’, ‘<samp>f2008</samp>’, ‘<samp>gnu</samp>’, or |
| ‘<samp>legacy</samp>’. The default value for <var>std</var> is ‘<samp>gnu</samp>’, which |
| specifies a superset of the Fortran 95 standard that includes all of the |
| extensions supported by GNU Fortran, although warnings will be given for |
| obsolete extensions not recommended for use in new code. The |
| ‘<samp>legacy</samp>’ value is equivalent but without the warnings for obsolete |
| extensions, and may be useful for old non-standard programs. The |
| ‘<samp>f95</samp>’, ‘<samp>f2003</samp>’ and ‘<samp>f2008</samp>’ values specify strict |
| conformance to the Fortran 95, Fortran 2003 and Fortran 2008 standards, |
| respectively; errors are given for all extensions beyond the relevant |
| language standard, and warnings are given for the Fortran 77 features |
| that are permitted but obsolescent in later standards. ‘<samp>-std=f2008ts</samp>’ |
| allows the Fortran 2008 standard including the additions of the |
| Technical Specification (TS) 29113 on Further Interoperability of Fortran |
| with C. |
| </p> |
| </dd> |
| </dl> |
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