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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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<div class="header">
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<p>
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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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</div>
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<hr>
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<a name="Options-to-request-or-suppress-errors-and-warnings"></a>
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<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>
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<a name="index-messages_002c-warning"></a>
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<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>-Wtabs</samp>, <samp>-Wintrinsic-shadow</samp>,
|
<samp>-Wline-truncation</samp>, <samp>-Wtarget-lifetime</samp>,
|
<samp>-Winteger-division</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>. For free-form source code, the default is
|
<samp>-Werror=line-truncation</samp> such that truncations are reported as
|
error.
|
</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. This
|
option does <em>not</em> imply <samp>-Wconversion</samp>.
|
</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>-Winteger-division</code></dt>
|
<dd><a name="index-Winteger_002ddivision"></a>
|
<a name="index-warnings_002c-integer-division"></a>
|
<a name="index-warnings_002c-division-of-integers"></a>
|
<p>Warn if a constant integer division truncates it result.
|
As an example, 3/5 evaluates to 0.
|
</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>-Wtabs</samp> will cause
|
a warning to be issued if a tab is encountered. Note, <samp>-Wtabs</samp>
|
is active for <samp>-pedantic</samp>, <samp>-std=f95</samp>, <samp>-std=f2003</samp>,
|
<samp>-std=f2008</samp>, <samp>-std=f2008ts</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. Enabled by default.
|
</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>-Wuse-without-only</code></dt>
|
<dd><a name="index-Wuse_002dwithout_002donly"></a>
|
<a name="index-warnings_002c-use-statements"></a>
|
<a name="index-intrinsic-1"></a>
|
<p>Warn if a <code>USE</code> statement has no <code>ONLY</code> qualifier and
|
thus implicitly imports all public entities of the used module.
|
</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 implied by <samp>-Wextra</samp> if also <samp>-Wunused</samp> or
|
<samp>-Wall</samp> is used.
|
</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.
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</p>
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<p>Some of these have no effect when compiling programs written in Fortran.
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