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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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<div class="header">
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<p>
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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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</div>
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<hr>
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<a name="Options-controlling-Fortran-dialect"></a>
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<h3 class="section">2.2 Options controlling Fortran dialect</h3>
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<a name="index-dialect-options"></a>
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<a name="index-language_002c-dialect-options"></a>
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<a name="index-options_002c-dialect"></a>
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<p>The following options control the details of the Fortran dialect
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accepted by the compiler:
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</p>
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<dl compact="compact">
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<dt><code>-ffree-form</code></dt>
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<dt><code>-ffixed-form</code></dt>
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<dd><a name="index-ffree_002dform"></a>
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<a name="index-ffixed_002dform"></a>
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<a name="index-options_002c-Fortran-dialect"></a>
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<a name="index-file-format_002c-free"></a>
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<a name="index-file-format_002c-fixed"></a>
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<p>Specify the layout used by the source file. The free form layout
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was introduced in Fortran 90. Fixed form was traditionally used in
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older Fortran programs. When neither option is specified, the source
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form is determined by the file extension.
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</p>
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</dd>
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<dt><code>-fall-intrinsics</code></dt>
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<dd><a name="index-fall_002dintrinsics"></a>
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<p>This option causes all intrinsic procedures (including the GNU-specific
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extensions) to be accepted. This can be useful with <samp>-std=f95</samp> to
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force standard-compliance but get access to the full range of intrinsics
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available with <code>gfortran</code>. As a consequence, <samp>-Wintrinsics-std</samp>
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will be ignored and no user-defined procedure with the same name as any
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intrinsic will be called except when it is explicitly declared <code>EXTERNAL</code>.
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</p>
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</dd>
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<dt><code>-fd-lines-as-code</code></dt>
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<dt><code>-fd-lines-as-comments</code></dt>
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<dd><a name="index-fd_002dlines_002das_002dcode"></a>
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<a name="index-fd_002dlines_002das_002dcomments"></a>
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<p>Enable special treatment for lines beginning with <code>d</code> or <code>D</code>
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in fixed form sources. If the <samp>-fd-lines-as-code</samp> option is
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given they are treated as if the first column contained a blank. If the
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<samp>-fd-lines-as-comments</samp> option is given, they are treated as
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comment lines.
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</p>
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</dd>
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<dt><code>-fdec</code></dt>
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<dd><a name="index-fdec"></a>
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<p>DEC compatibility mode. Enables extensions and other features that mimic
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the default behavior of older compilers (such as DEC).
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These features are non-standard and should be avoided at all costs.
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For details on GNU Fortran’s implementation of these extensions see the
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full documentation.
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</p>
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<p>Other flags enabled by this switch are:
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<samp>-fdollar-ok</samp> <samp>-fcray-pointer</samp> <samp>-fdec-structure</samp>
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</p>
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</dd>
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<dt><code>-fdec-structure</code></dt>
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<dd><a name="index-fdec_002dstructure"></a>
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<p>Enable DEC <code>STRUCTURE</code> and <code>RECORD</code> as well as <code>UNION</code>,
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<code>MAP</code>, and dot (’.’) as a member separator (in addition to ’%’). This is
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provided for compatibility only; Fortran 90 derived types should be used
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instead where possible.
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</p>
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</dd>
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<dt><code>-fdollar-ok</code></dt>
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<dd><a name="index-fdollar_002dok"></a>
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<a name="index-_0024"></a>
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<a name="index-symbol-names"></a>
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<a name="index-character-set"></a>
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<p>Allow ‘<samp>$</samp>’ as a valid non-first character in a symbol name. Symbols
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that start with ‘<samp>$</samp>’ are rejected since it is unclear which rules to
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apply to implicit typing as different vendors implement different rules.
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Using ‘<samp>$</samp>’ in <code>IMPLICIT</code> statements is also rejected.
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</p>
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</dd>
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<dt><code>-fbackslash</code></dt>
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<dd><a name="index-backslash-1"></a>
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<a name="index-backslash"></a>
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<a name="index-escape-characters"></a>
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<p>Change the interpretation of backslashes in string literals from a single
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backslash character to “C-style” escape characters. The following
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combinations are expanded <code>\a</code>, <code>\b</code>, <code>\f</code>, <code>\n</code>,
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<code>\r</code>, <code>\t</code>, <code>\v</code>, <code>\\</code>, and <code>\0</code> to the ASCII
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characters alert, backspace, form feed, newline, carriage return,
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horizontal tab, vertical tab, backslash, and NUL, respectively.
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Additionally, <code>\x</code><var>nn</var>, <code>\u</code><var>nnnn</var> and
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<code>\U</code><var>nnnnnnnn</var> (where each <var>n</var> is a hexadecimal digit) are
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translated into the Unicode characters corresponding to the specified code
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points. All other combinations of a character preceded by \ are
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unexpanded.
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</p>
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</dd>
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<dt><code>-fmodule-private</code></dt>
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<dd><a name="index-fmodule_002dprivate"></a>
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<a name="index-module-entities"></a>
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<a name="index-private"></a>
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<p>Set the default accessibility of module entities to <code>PRIVATE</code>.
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Use-associated entities will not be accessible unless they are explicitly
|
declared as <code>PUBLIC</code>.
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</p>
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</dd>
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<dt><code>-ffixed-line-length-<var>n</var></code></dt>
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<dd><a name="index-ffixed_002dline_002dlength_002dn"></a>
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<a name="index-file-format_002c-fixed-1"></a>
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<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.
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</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>
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</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>
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</dd>
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<dt><code>-fmax-identifier-length=<var>n</var></code></dt>
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<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>
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<p>Enable the Cray pointer extension, which provides C-like pointer
|
functionality.
|
</p>
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</dd>
|
<dt><code>-fopenacc</code></dt>
|
<dd><a name="index-fopenacc"></a>
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<a name="index-OpenACC"></a>
|
<p>Enable the OpenACC extensions. This includes OpenACC <code>!$acc</code>
|
directives in free form and <code>c$acc</code>, <code>*$acc</code> and
|
<code>!$acc</code> directives in fixed form, <code>!$</code> conditional
|
compilation sentinels in free form and <code>c$</code>, <code>*$</code> and
|
<code>!$</code> sentinels in fixed form, and when linking arranges for the
|
OpenACC runtime library to be linked in.
|
</p>
|
<p>Note that this is an experimental feature, incomplete, and subject to
|
change in future versions of GCC. See
|
<a href="https://gcc.gnu.org/wiki/OpenACC">https://gcc.gnu.org/wiki/OpenACC</a><!-- /@w --> for more information.
|
</p>
|
</dd>
|
<dt><code>-fopenmp</code></dt>
|
<dd><a name="index-fopenmp"></a>
|
<a name="index-OpenMP"></a>
|
<p>Enable the OpenMP extensions. This includes OpenMP <code>!$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 and TS 18508 on Additional Parallel Features in Fortran.
|
</p>
|
</dd>
|
</dl>
|
|
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|
<p>
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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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