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<h3 class="section">3.2 Options Controlling the Kind of Output</h3>
<p>Compilation can involve up to four stages: preprocessing, compilation
proper, assembly and linking, always in that order. GCC is capable of
preprocessing and compiling several files either into several
assembler input files, or into one assembler input file; then each
assembler input file produces an object file, and linking combines all
the object files (those newly compiled, and those specified as input)
into an executable file.
<p><a name="index-file-name-suffix-76"></a>For any given input file, the file name suffix determines what kind of
compilation is done:
<dl>
<dt><var>file</var><code>.c</code><dd>C source code that must be preprocessed.
<br><dt><var>file</var><code>.i</code><dd>C source code that should not be preprocessed.
<br><dt><var>file</var><code>.ii</code><dd>C++ source code that should not be preprocessed.
<br><dt><var>file</var><code>.m</code><dd>Objective-C source code. Note that you must link with the <samp><span class="file">libobjc</span></samp>
library to make an Objective-C program work.
<br><dt><var>file</var><code>.mi</code><dd>Objective-C source code that should not be preprocessed.
<br><dt><var>file</var><code>.mm</code><dt><var>file</var><code>.M</code><dd>Objective-C++ source code. Note that you must link with the <samp><span class="file">libobjc</span></samp>
library to make an Objective-C++ program work. Note that ‘<samp><span class="samp">.M</span></samp>’ refers
to a literal capital M.
<br><dt><var>file</var><code>.mii</code><dd>Objective-C++ source code that should not be preprocessed.
<br><dt><var>file</var><code>.h</code><dd>C, C++, Objective-C or Objective-C++ header file to be turned into a
precompiled header (default), or C, C++ header file to be turned into an
Ada spec (via the <samp><span class="option">-fdump-ada-spec</span></samp> switch).
<br><dt><var>file</var><code>.cc</code><dt><var>file</var><code>.cp</code><dt><var>file</var><code>.cxx</code><dt><var>file</var><code>.cpp</code><dt><var>file</var><code>.CPP</code><dt><var>file</var><code>.c++</code><dt><var>file</var><code>.C</code><dd>C++ source code that must be preprocessed. Note that in ‘<samp><span class="samp">.cxx</span></samp>’,
the last two letters must both be literally ‘<samp><span class="samp">x</span></samp>’. Likewise,
‘<samp><span class="samp">.C</span></samp>’ refers to a literal capital C.
<br><dt><var>file</var><code>.mm</code><dt><var>file</var><code>.M</code><dd>Objective-C++ source code that must be preprocessed.
<br><dt><var>file</var><code>.mii</code><dd>Objective-C++ source code that should not be preprocessed.
<br><dt><var>file</var><code>.hh</code><dt><var>file</var><code>.H</code><dt><var>file</var><code>.hp</code><dt><var>file</var><code>.hxx</code><dt><var>file</var><code>.hpp</code><dt><var>file</var><code>.HPP</code><dt><var>file</var><code>.h++</code><dt><var>file</var><code>.tcc</code><dd>C++ header file to be turned into a precompiled header or Ada spec.
<br><dt><var>file</var><code>.f</code><dt><var>file</var><code>.for</code><dt><var>file</var><code>.ftn</code><dd>Fixed form Fortran source code that should not be preprocessed.
<br><dt><var>file</var><code>.F</code><dt><var>file</var><code>.FOR</code><dt><var>file</var><code>.fpp</code><dt><var>file</var><code>.FPP</code><dt><var>file</var><code>.FTN</code><dd>Fixed form Fortran source code that must be preprocessed (with the traditional
preprocessor).
<br><dt><var>file</var><code>.f90</code><dt><var>file</var><code>.f95</code><dt><var>file</var><code>.f03</code><dt><var>file</var><code>.f08</code><dd>Free form Fortran source code that should not be preprocessed.
<br><dt><var>file</var><code>.F90</code><dt><var>file</var><code>.F95</code><dt><var>file</var><code>.F03</code><dt><var>file</var><code>.F08</code><dd>Free form Fortran source code that must be preprocessed (with the
traditional preprocessor).
<br><dt><var>file</var><code>.go</code><dd>Go source code.
<!-- FIXME: Descriptions of Java file types. -->
<!-- @var{file}.java -->
<!-- @var{file}.class -->
<!-- @var{file}.zip -->
<!-- @var{file}.jar -->
<br><dt><var>file</var><code>.ads</code><dd>Ada source code file that contains a library unit declaration (a
declaration of a package, subprogram, or generic, or a generic
instantiation), or a library unit renaming declaration (a package,
generic, or subprogram renaming declaration). Such files are also
called <dfn>specs</dfn>.
<br><dt><var>file</var><code>.adb</code><dd>Ada source code file containing a library unit body (a subprogram or
package body). Such files are also called <dfn>bodies</dfn>.
<!-- GCC also knows about some suffixes for languages not yet included: -->
<!-- Pascal: -->
<!-- @var{file}.p -->
<!-- @var{file}.pas -->
<!-- Ratfor: -->
<!-- @var{file}.r -->
<br><dt><var>file</var><code>.s</code><dd>Assembler code.
<br><dt><var>file</var><code>.S</code><dt><var>file</var><code>.sx</code><dd>Assembler code that must be preprocessed.
<br><dt><var>other</var><dd>An object file to be fed straight into linking.
Any file name with no recognized suffix is treated this way.
</dl>
<p><a name="index-x-77"></a>You can specify the input language explicitly with the <samp><span class="option">-x</span></samp> option:
<dl>
<dt><code>-x </code><var>language</var><dd>Specify explicitly the <var>language</var> for the following input files
(rather than letting the compiler choose a default based on the file
name suffix). This option applies to all following input files until
the next <samp><span class="option">-x</span></samp> option. Possible values for <var>language</var> are:
<pre class="smallexample"> c c-header cpp-output
c++ c++-header c++-cpp-output
objective-c objective-c-header objective-c-cpp-output
objective-c++ objective-c++-header objective-c++-cpp-output
assembler assembler-with-cpp
ada
f77 f77-cpp-input f95 f95-cpp-input
go
java
</pre>
<br><dt><code>-x none</code><dd>Turn off any specification of a language, so that subsequent files are
handled according to their file name suffixes (as they are if <samp><span class="option">-x</span></samp>
has not been used at all).
<br><dt><code>-pass-exit-codes</code><dd><a name="index-pass_002dexit_002dcodes-78"></a>Normally the <samp><span class="command">gcc</span></samp> program exits with the code of 1 if any
phase of the compiler returns a non-success return code. If you specify
<samp><span class="option">-pass-exit-codes</span></samp>, the <samp><span class="command">gcc</span></samp> program instead returns with
the numerically highest error produced by any phase returning an error
indication. The C, C++, and Fortran front ends return 4 if an internal
compiler error is encountered.
</dl>
<p>If you only want some of the stages of compilation, you can use
<samp><span class="option">-x</span></samp> (or filename suffixes) to tell <samp><span class="command">gcc</span></samp> where to start, and
one of the options <samp><span class="option">-c</span></samp>, <samp><span class="option">-S</span></samp>, or <samp><span class="option">-E</span></samp> to say where
<samp><span class="command">gcc</span></samp> is to stop. Note that some combinations (for example,
‘<samp><span class="samp">-x cpp-output -E</span></samp>’) instruct <samp><span class="command">gcc</span></samp> to do nothing at all.
<dl>
<dt><code>-c</code><dd><a name="index-c-79"></a>Compile or assemble the source files, but do not link. The linking
stage simply is not done. The ultimate output is in the form of an
object file for each source file.
<p>By default, the object file name for a source file is made by replacing
the suffix ‘<samp><span class="samp">.c</span></samp>’, ‘<samp><span class="samp">.i</span></samp>’, ‘<samp><span class="samp">.s</span></samp>’, etc., with ‘<samp><span class="samp">.o</span></samp>’.
<p>Unrecognized input files, not requiring compilation or assembly, are
ignored.
<br><dt><code>-S</code><dd><a name="index-S-80"></a>Stop after the stage of compilation proper; do not assemble. The output
is in the form of an assembler code file for each non-assembler input
file specified.
<p>By default, the assembler file name for a source file is made by
replacing the suffix ‘<samp><span class="samp">.c</span></samp>’, ‘<samp><span class="samp">.i</span></samp>’, etc., with ‘<samp><span class="samp">.s</span></samp>’.
<p>Input files that don't require compilation are ignored.
<br><dt><code>-E</code><dd><a name="index-E-81"></a>Stop after the preprocessing stage; do not run the compiler proper. The
output is in the form of preprocessed source code, which is sent to the
standard output.
<p>Input files that don't require preprocessing are ignored.
<p><a name="index-output-file-option-82"></a><br><dt><code>-o </code><var>file</var><dd><a name="index-o-83"></a>Place output in file <var>file</var>. This applies to whatever
sort of output is being produced, whether it be an executable file,
an object file, an assembler file or preprocessed C code.
<p>If <samp><span class="option">-o</span></samp> is not specified, the default is to put an executable
file in <samp><span class="file">a.out</span></samp>, the object file for
<samp><var>source</var><span class="file">.</span><var>suffix</var></samp> in <samp><var>source</var><span class="file">.o</span></samp>, its
assembler file in <samp><var>source</var><span class="file">.s</span></samp>, a precompiled header file in
<samp><var>source</var><span class="file">.</span><var>suffix</var><span class="file">.gch</span></samp>, and all preprocessed C source on
standard output.
<br><dt><code>-v</code><dd><a name="index-v-84"></a>Print (on standard error output) the commands executed to run the stages
of compilation. Also print the version number of the compiler driver
program and of the preprocessor and the compiler proper.
<br><dt><code>-###</code><dd><a name="index-g_t_0023_0023_0023-85"></a>Like <samp><span class="option">-v</span></samp> except the commands are not executed and arguments
are quoted unless they contain only alphanumeric characters or <code>./-_</code>.
This is useful for shell scripts to capture the driver-generated command lines.
<br><dt><code>-pipe</code><dd><a name="index-pipe-86"></a>Use pipes rather than temporary files for communication between the
various stages of compilation. This fails to work on some systems where
the assembler is unable to read from a pipe; but the GNU assembler has
no trouble.
<br><dt><code>--help</code><dd><a name="index-help-87"></a>Print (on the standard output) a description of the command-line options
understood by <samp><span class="command">gcc</span></samp>. If the <samp><span class="option">-v</span></samp> option is also specified
then <samp><span class="option">--help</span></samp> is also passed on to the various processes
invoked by <samp><span class="command">gcc</span></samp>, so that they can display the command-line options
they accept. If the <samp><span class="option">-Wextra</span></samp> option has also been specified
(prior to the <samp><span class="option">--help</span></samp> option), then command-line options that
have no documentation associated with them are also displayed.
<br><dt><code>--target-help</code><dd><a name="index-target_002dhelp-88"></a>Print (on the standard output) a description of target-specific command-line
options for each tool. For some targets extra target-specific
information may also be printed.
<br><dt><code>--help={</code><var>class</var><span class="roman">|[</span><code>^</code><span class="roman">]</span><var>qualifier</var><code>}</code><span class="roman">[</span><code>,...</code><span class="roman">]</span><dd>Print (on the standard output) a description of the command-line
options understood by the compiler that fit into all specified classes
and qualifiers. These are the supported classes:
<dl>
<dt>‘<samp><span class="samp">optimizers</span></samp>’<dd>Display all of the optimization options supported by the
compiler.
<br><dt>‘<samp><span class="samp">warnings</span></samp>’<dd>Display all of the options controlling warning messages
produced by the compiler.
<br><dt>‘<samp><span class="samp">target</span></samp>’<dd>Display target-specific options. Unlike the
<samp><span class="option">--target-help</span></samp> option however, target-specific options of the
linker and assembler are not displayed. This is because those
tools do not currently support the extended <samp><span class="option">--help=</span></samp> syntax.
<br><dt>‘<samp><span class="samp">params</span></samp>’<dd>Display the values recognized by the <samp><span class="option">--param</span></samp>
option.
<br><dt><var>language</var><dd>Display the options supported for <var>language</var>, where
<var>language</var> is the name of one of the languages supported in this
version of GCC.
<br><dt>‘<samp><span class="samp">common</span></samp>’<dd>Display the options that are common to all languages.
</dl>
<p>These are the supported qualifiers:
<dl>
<dt>‘<samp><span class="samp">undocumented</span></samp>’<dd>Display only those options that are undocumented.
<br><dt>‘<samp><span class="samp">joined</span></samp>’<dd>Display options taking an argument that appears after an equal
sign in the same continuous piece of text, such as:
‘<samp><span class="samp">--help=target</span></samp>’.
<br><dt>‘<samp><span class="samp">separate</span></samp>’<dd>Display options taking an argument that appears as a separate word
following the original option, such as: ‘<samp><span class="samp">-o output-file</span></samp>’.
</dl>
<p>Thus for example to display all the undocumented target-specific
switches supported by the compiler, use:
<pre class="smallexample"> --help=target,undocumented
</pre>
<p>The sense of a qualifier can be inverted by prefixing it with the
‘<samp><span class="samp">^</span></samp>’ character, so for example to display all binary warning
options (i.e., ones that are either on or off and that do not take an
argument) that have a description, use:
<pre class="smallexample"> --help=warnings,^joined,^undocumented
</pre>
<p>The argument to <samp><span class="option">--help=</span></samp> should not consist solely of inverted
qualifiers.
<p>Combining several classes is possible, although this usually
restricts the output so much that there is nothing to display. One
case where it does work, however, is when one of the classes is
<var>target</var>. For example, to display all the target-specific
optimization options, use:
<pre class="smallexample"> --help=target,optimizers
</pre>
<p>The <samp><span class="option">--help=</span></samp> option can be repeated on the command line. Each
successive use displays its requested class of options, skipping
those that have already been displayed.
<p>If the <samp><span class="option">-Q</span></samp> option appears on the command line before the
<samp><span class="option">--help=</span></samp> option, then the descriptive text displayed by
<samp><span class="option">--help=</span></samp> is changed. Instead of describing the displayed
options, an indication is given as to whether the option is enabled,
disabled or set to a specific value (assuming that the compiler
knows this at the point where the <samp><span class="option">--help=</span></samp> option is used).
<p>Here is a truncated example from the ARM port of <samp><span class="command">gcc</span></samp>:
<pre class="smallexample"> % gcc -Q -mabi=2 --help=target -c
The following options are target specific:
-mabi= 2
-mabort-on-noreturn [disabled]
-mapcs [disabled]
</pre>
<p>The output is sensitive to the effects of previous command-line
options, so for example it is possible to find out which optimizations
are enabled at <samp><span class="option">-O2</span></samp> by using:
<pre class="smallexample"> -Q -O2 --help=optimizers
</pre>
<p>Alternatively you can discover which binary optimizations are enabled
by <samp><span class="option">-O3</span></samp> by using:
<pre class="smallexample"> gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
diff /tmp/O2-opts /tmp/O3-opts | grep enabled
</pre>
<br><dt><code>-no-canonical-prefixes</code><dd><a name="index-no_002dcanonical_002dprefixes-89"></a>Do not expand any symbolic links, resolve references to ‘<samp><span class="samp">/../</span></samp>’
or ‘<samp><span class="samp">/./</span></samp>’, or make the path absolute when generating a relative
prefix.
<br><dt><code>--version</code><dd><a name="index-version-90"></a>Display the version number and copyrights of the invoked GCC.
<br><dt><code>-wrapper</code><dd><a name="index-wrapper-91"></a>Invoke all subcommands under a wrapper program. The name of the
wrapper program and its parameters are passed as a comma separated
list.
<pre class="smallexample"> gcc -c t.c -wrapper gdb,--args
</pre>
<p class="noindent">This invokes all subprograms of <samp><span class="command">gcc</span></samp> under
‘<samp><span class="samp">gdb --args</span></samp>’, thus the invocation of <samp><span class="command">cc1</span></samp> is
‘<samp><span class="samp">gdb --args cc1 ...</span></samp>’.
<br><dt><code>-fplugin=</code><var>name</var><code>.so</code><dd><a name="index-fplugin-92"></a>Load the plugin code in file <var>name</var>.so, assumed to be a
shared object to be dlopen'd by the compiler. The base name of
the shared object file is used to identify the plugin for the
purposes of argument parsing (See
<samp><span class="option">-fplugin-arg-</span><var>name</var><span class="option">-</span><var>key</var><span class="option">=</span><var>value</var></samp> below).
Each plugin should define the callback functions specified in the
Plugins API.
<br><dt><code>-fplugin-arg-</code><var>name</var><code>-</code><var>key</var><code>=</code><var>value</var><dd><a name="index-fplugin_002darg-93"></a>Define an argument called <var>key</var> with a value of <var>value</var>
for the plugin called <var>name</var>.
<br><dt><code>-fdump-ada-spec</code><span class="roman">[</span><code>-slim</code><span class="roman">]</span><dd><a name="index-fdump_002dada_002dspec-94"></a>For C and C++ source and include files, generate corresponding Ada specs.
See <a href="../gnat_ugn/Generating-Ada-Bindings-for-C-and-C_002b_002b-headers.html#Generating-Ada-Bindings-for-C-and-C_002b_002b-headers">Generating Ada Bindings for C and C++ headers</a>, which provides detailed documentation on this feature.
<br><dt><code>-fada-spec-parent=</code><var>unit</var><dd><a name="index-fada_002dspec_002dparent-95"></a>In conjunction with <samp><span class="option">-fdump-ada-spec[-slim]</span></samp> above, generate
Ada specs as child units of parent <var>unit</var>.
<br><dt><code>-fdump-go-spec=</code><var>file</var><dd><a name="index-fdump_002dgo_002dspec-96"></a>For input files in any language, generate corresponding Go
declarations in <var>file</var>. This generates Go <code>const</code>,
<code>type</code>, <code>var</code>, and <code>func</code> declarations which may be a
useful way to start writing a Go interface to code written in some
other language.
<!-- This file is designed to be included in manuals that use -->
<!-- expandargv. -->
<br><dt><code>@</code><var>file</var><dd>Read command-line options from <var>file</var>. The options read are
inserted in place of the original @<var>file</var> option. If <var>file</var>
does not exist, or cannot be read, then the option will be treated
literally, and not removed.
<p>Options in <var>file</var> are separated by whitespace. A whitespace
character may be included in an option by surrounding the entire
option in either single or double quotes. Any character (including a
backslash) may be included by prefixing the character to be included
with a backslash. The <var>file</var> may itself contain additional
@<var>file</var> options; any such options will be processed recursively.
</dl>
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