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<a name="Invoking-GCC"></a>
<div class="header">
<p>
Next: <a href="C-Implementation.html#C-Implementation" accesskey="n" rel="next">C Implementation</a>, Previous: <a href="Standards.html#Standards" accesskey="p" rel="prev">Standards</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> &nbsp; [<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="GCC-Command-Options"></a>
<h2 class="chapter">3 GCC Command Options</h2>
<a name="index-GCC-command-options"></a>
<a name="index-command-options"></a>
<a name="index-options_002c-GCC-command"></a>

<p>When you invoke GCC, it normally does preprocessing, compilation,
assembly and linking.  The &ldquo;overall options&rdquo; allow you to stop this
process at an intermediate stage.  For example, the <samp>-c</samp> option
says not to run the linker.  Then the output consists of object files
output by the assembler.
See <a href="Overall-Options.html#Overall-Options">Options Controlling the Kind of Output</a>.
</p>
<p>Other options are passed on to one or more stages of processing.  Some options
control the preprocessor and others the compiler itself.  Yet other
options control the assembler and linker; most of these are not
documented here, since you rarely need to use any of them.
</p>
<a name="index-C-compilation-options"></a>
<p>Most of the command-line options that you can use with GCC are useful
for C programs; when an option is only useful with another language
(usually C++), the explanation says so explicitly.  If the description
for a particular option does not mention a source language, you can use
that option with all supported languages.
</p>
<a name="index-cross-compiling"></a>
<a name="index-specifying-machine-version"></a>
<a name="index-specifying-compiler-version-and-target-machine"></a>
<a name="index-compiler-version_002c-specifying"></a>
<a name="index-target-machine_002c-specifying"></a>
<p>The usual way to run GCC is to run the executable called <code>gcc</code>, or
<code><var>machine</var>-gcc</code> when cross-compiling, or
<code><var>machine</var>-gcc-<var>version</var></code> to run a specific version of GCC.
When you compile C++ programs, you should invoke GCC as <code>g++</code> 
instead.  See <a href="Invoking-G_002b_002b.html#Invoking-G_002b_002b">Compiling C++ Programs</a>, 
for information about the differences in behavior between <code>gcc</code> 
and <code>g++</code> when compiling C++ programs.
</p>
<a name="index-grouping-options"></a>
<a name="index-options_002c-grouping"></a>
<p>The <code>gcc</code> program accepts options and file names as operands.  Many
options have multi-letter names; therefore multiple single-letter options
may <em>not</em> be grouped: <samp>-dv</samp> is very different from &lsquo;<samp><span class="nolinebreak">-d</span>&nbsp;<span class="nolinebreak">-v</span></samp>&rsquo;<!-- /@w -->.
</p>
<a name="index-order-of-options"></a>
<a name="index-options_002c-order"></a>
<p>You can mix options and other arguments.  For the most part, the order
you use doesn&rsquo;t matter.  Order does matter when you use several
options of the same kind; for example, if you specify <samp>-L</samp> more
than once, the directories are searched in the order specified.  Also,
the placement of the <samp>-l</samp> option is significant.
</p>
<p>Many options have long names starting with &lsquo;<samp>-f</samp>&rsquo; or with
&lsquo;<samp>-W</samp>&rsquo;&mdash;for example,
<samp>-fmove-loop-invariants</samp>, <samp>-Wformat</samp> and so on.  Most of
these have both positive and negative forms; the negative form of
<samp>-ffoo</samp> is <samp>-fno-foo</samp>.  This manual documents
only one of these two forms, whichever one is not the default.
</p>
<p>Some options take one or more arguments typically separated either
by a space or by the equals sign (&lsquo;<samp>=</samp>&rsquo;) from the option name.
Unless documented otherwise, an argument can be either numeric or
a string.  Numeric arguments must typically be small unsigned decimal
or hexadecimal integers.  Hexadecimal arguments must begin with
the &lsquo;<samp>0x</samp>&rsquo; prefix.  Arguments to options that specify a size
threshold of some sort may be arbitrarily large decimal or hexadecimal
integers followed by a byte size suffix designating a multiple of bytes
such as <code>kB</code> and <code>KiB</code> for kilobyte and kibibyte, respectively,
<code>MB</code> and <code>MiB</code> for megabyte and mebibyte, <code>GB</code> and
<code>GiB</code> for gigabyte and gigibyte, and so on.  Such arguments are
designated by <var>byte-size</var> in the following text.  Refer to the NIST,
IEC, and other relevant national and international standards for the full
listing and explanation of the binary and decimal byte size prefixes.
</p>

<p>See <a href="Option-Index.html#Option-Index">Option Index</a>, for an index to GCC&rsquo;s options.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">&bull; <a href="Option-Summary.html#Option-Summary" accesskey="1">Option Summary</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Brief list of all options, without explanations.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Overall-Options.html#Overall-Options" accesskey="2">Overall Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Controlling the kind of output:
                        an executable, object files, assembler files,
                        or preprocessed source.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Invoking-G_002b_002b.html#Invoking-G_002b_002b" accesskey="3">Invoking G++</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Compiling C++ programs.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="C-Dialect-Options.html#C-Dialect-Options" accesskey="4">C Dialect Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Controlling the variant of C language compiled.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="C_002b_002b-Dialect-Options.html#C_002b_002b-Dialect-Options" accesskey="5">C++ Dialect Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Variations on C++.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Objective_002dC-and-Objective_002dC_002b_002b-Dialect-Options.html#Objective_002dC-and-Objective_002dC_002b_002b-Dialect-Options" accesskey="6">Objective-C and Objective-C++ Dialect Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Variations on Objective-C
                        and Objective-C++.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Diagnostic-Message-Formatting-Options.html#Diagnostic-Message-Formatting-Options" accesskey="7">Diagnostic Message Formatting Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Controlling how diagnostics should
                        be formatted.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Warning-Options.html#Warning-Options" accesskey="8">Warning Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">How picky should the compiler be?
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Static-Analyzer-Options.html#Static-Analyzer-Options" accesskey="9">Static Analyzer Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">More expensive warnings.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Debugging-Options.html#Debugging-Options">Debugging Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Producing debuggable code.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Optimize-Options.html#Optimize-Options">Optimize Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">How much optimization?
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Instrumentation-Options.html#Instrumentation-Options">Instrumentation Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Enabling profiling and extra run-time error checking.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Preprocessor-Options.html#Preprocessor-Options">Preprocessor Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Controlling header files and macro definitions.
                         Also, getting dependency information for Make.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Assembler-Options.html#Assembler-Options">Assembler Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Passing options to the assembler.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Link-Options.html#Link-Options">Link Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Specifying libraries and so on.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Directory-Options.html#Directory-Options">Directory Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Where to find header files and libraries.
                        Where to find the compiler executable files.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Code-Gen-Options.html#Code-Gen-Options">Code Gen Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Specifying conventions for function calls, data layout
                        and register usage.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Developer-Options.html#Developer-Options">Developer Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Printing GCC configuration info, statistics, and
                        debugging dumps.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Submodel-Options.html#Submodel-Options">Submodel Options</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Target-specific options, such as compiling for a
                        specific processor variant.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Spec-Files.html#Spec-Files">Spec Files</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">How to pass switches to sub-processes.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Environment-Variables.html#Environment-Variables">Environment Variables</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Env vars that affect GCC.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Precompiled-Headers.html#Precompiled-Headers">Precompiled Headers</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Compiling a header once, and using it many times.
</td></tr>
</table>


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