preprocessor-options.html

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scanning <var>file</var> is thrown away.  Macros it defines remain defined. 
This allows you to acquire all the macros from a header without also
processing its declarations.

     <p>All files specified by <code>-imacros</code> are processed before all files
specified by <code>-include</code>.

     <br><dt><code>-idirafter </code><var>dir</var><code></code>
     <dd>Search <var>dir</var> for header files, but do it <em>after</em> all
directories specified with <code>-I</code> and the standard system directories
have been exhausted.  <var>dir</var> is treated as a system include directory.

     <br><dt><code>-iprefix </code><var>prefix</var><code></code>
     <dd>Specify <var>prefix</var> as the prefix for subsequent <code>-iwithprefix</code>
options.  If the prefix represents a directory, you should include the
final <code>/</code>.

     <br><dt><code>-iwithprefix </code><var>dir</var><code></code>
     <dd><dt><code>-iwithprefixbefore </code><var>dir</var><code></code>
     <dd>Append <var>dir</var> to the prefix specified previously with
<code>-iprefix</code>, and add the resulting directory to the include search
path.  <code>-iwithprefixbefore</code> puts it in the same place <code>-I</code>
would; <code>-iwithprefix</code> puts it where <code>-idirafter</code> would.

     <br><dt><code>-isystem </code><var>dir</var><code></code>
     <dd>Search <var>dir</var> for header files, after all directories specified by
<code>-I</code> but before the standard system directories.  Mark it
as a system directory, so that it gets the same special treatment as
is applied to the standard system directories.

     <br><dt><code>-fdollars-in-identifiers</code>
     <dd><a name="fdollars-in-identifiers"></a>
Accept <code>$</code> in identifiers.

     <br><dt><code>-fpreprocessed</code>
     <dd>Indicate to the preprocessor that the input file has already been
preprocessed.  This suppresses things like macro expansion, trigraph
conversion, escaped newline splicing, and processing of most directives. 
The preprocessor still recognizes and removes comments, so that you can
pass a file preprocessed with <code>-C</code> to the compiler without
problems.  In this mode the integrated preprocessor is little more than
a tokenizer for the front ends.

     <p><code>-fpreprocessed</code> is implicit if the input file has one of the
extensions <code>.i</code>, <code>.ii</code> or <code>.mi</code>.  These are the
extensions that GCC uses for preprocessed files created by
<code>-save-temps</code>.

     <br><dt><code>-ftabstop=</code><var>width</var><code></code>
     <dd>Set the distance between tab stops.  This helps the preprocessor report
correct column numbers in warnings or errors, even if tabs appear on the
line.  If the value is less than 1 or greater than 100, the option is
ignored.  The default is 8.

     <br><dt><code>-fexec-charset=</code><var>charset</var><code></code>
     <dd>Set the execution character set, used for string and character
constants.  The default is UTF-8.  <var>charset</var> can be any encoding
supported by the system's <code>iconv</code> library routine.

     <br><dt><code>-fwide-exec-charset=</code><var>charset</var><code></code>
     <dd>Set the wide execution character set, used for wide string and
character constants.  The default is UTF-32 or UTF-16, whichever
corresponds to the width of <code>wchar_t</code>.  As with
<code>-fexec-charset</code>, <var>charset</var> can be any encoding supported
by the system's <code>iconv</code> library routine; however, you will have
problems with encodings that do not fit exactly in <code>wchar_t</code>.

     <br><dt><code>-finput-charset=</code><var>charset</var><code></code>
     <dd>Set the input character set, used for translation from the character
set of the input file to the source character set used by GCC. If the
locale does not specify, or GCC cannot get this information from the
locale, the default is UTF-8. This can be overridden by either the locale
or this command line option. Currently the command line option takes
precedence if there's a conflict. <var>charset</var> can be any encoding
supported by the system's <code>iconv</code> library routine.

     <br><dt><code>-fworking-directory</code>
     <dd>Enable generation of linemarkers in the preprocessor output that will
let the compiler know the current working directory at the time of
preprocessing.  When this option is enabled, the preprocessor will
emit, after the initial linemarker, a second linemarker with the
current working directory followed by two slashes.  GCC will use this
directory, when it's present in the preprocessed input, as the
directory emitted as the current working directory in some debugging
information formats.  This option is implicitly enabled if debugging
information is enabled, but this can be inhibited with the negated
form <code>-fno-working-directory</code>.  If the <code>-P</code> flag is
present in the command line, this option has no effect, since no
<code>#line</code> directives are emitted whatsoever.

     <br><dt><code>-fno-show-column</code>
     <dd>Do not print column numbers in diagnostics.  This may be necessary if
diagnostics are being scanned by a program that does not understand the
column numbers, such as <code>dejagnu</code>.

     <br><dt><code>-A </code><var>predicate</var><code>=</code><var>answer</var><code></code>
     <dd>Make an assertion with the predicate <var>predicate</var> and answer
<var>answer</var>.  This form is preferred to the older form <code>-A
</code><var>predicate</var><code>(</code><var>answer</var><code>)</code>, which is still supported, because
it does not use shell special characters.

     <br><dt><code>-A -</code><var>predicate</var><code>=</code><var>answer</var><code></code>
     <dd>Cancel an assertion with the predicate <var>predicate</var> and answer
<var>answer</var>.

     <br><dt><code>-dCHARS</code>
     <dd><var>CHARS</var> is a sequence of one or more of the following characters,
and must not be preceded by a space.  Other characters are interpreted
by the compiler proper, or reserved for future versions of GCC, and so
are silently ignored.  If you specify characters whose behavior
conflicts, the result is undefined.

          <dl>
<dt><code>M</code>
          <dd>Instead of the normal output, generate a list of <code>#define</code>
directives for all the macros defined during the execution of the
preprocessor, including predefined macros.  This gives you a way of
finding out what is predefined in your version of the preprocessor. 
Assuming you have no file <code>foo.h</code>, the command

          <pre class="smallexample">               touch foo.h; cpp -dM foo.h
               </pre>

          <p>will show all the predefined macros.

          <br><dt><code>D</code>
          <dd>Like <code>M</code> except in two respects: it does <em>not</em> include the
predefined macros, and it outputs <em>both</em> the <code>#define</code>
directives and the result of preprocessing.  Both kinds of output go to
the standard output file.

          <br><dt><code>N</code>
          <dd>Like <code>D</code>, but emit only the macro names, not their expansions.

          <br><dt><code>I</code>
          <dd>Output <code>#include</code> directives in addition to the result of
preprocessing. 
</dl>

     <br><dt><code>-P</code>
     <dd>Inhibit generation of linemarkers in the output from the preprocessor. 
This might be useful when running the preprocessor on something that is
not C code, and will be sent to a program which might be confused by the
linemarkers.

     <br><dt><code>-C</code>
     <dd>Do not discard comments.  All comments are passed through to the output
file, except for comments in processed directives, which are deleted
along with the directive.

     <p>You should be prepared for side effects when using <code>-C</code>; it
causes the preprocessor to treat comments as tokens in their own right. 
For example, comments appearing at the start of what would be a
directive line have the effect of turning that line into an ordinary
source line, since the first token on the line is no longer a <code>#</code>.

     <br><dt><code>-CC</code>
     <dd>Do not discard comments, including during macro expansion.  This is
like <code>-C</code>, except that comments contained within macros are
also passed through to the output file where the macro is expanded.

     <p>In addition to the side-effects of the <code>-C</code> option, the
<code>-CC</code> option causes all C++-style comments inside a macro
to be converted to C-style comments.  This is to prevent later use
of that macro from inadvertently commenting out the remainder of
the source line.

     <p>The <code>-CC</code> option is generally used to support lint comments.

     <br><dt><code>-traditional-cpp</code>
     <dd>Try to imitate the behavior of old-fashioned C preprocessors, as
opposed to ISO C preprocessors.

     <br><dt><code>-trigraphs</code>
     <dd>Process trigraph sequences. 
These are three-character sequences, all starting with <code>??</code>, that
are defined by ISO C to stand for single characters.  For example,
<code>??/</code> stands for <code>\</code>, so <code>'??/n'</code> is a character
constant for a newline.  By default, GCC ignores trigraphs, but in
standard-conforming modes it converts them.  See the <code>-std</code> and
<code>-ansi</code> options.

     <p>The nine trigraphs and their replacements are

     <pre class="smallexample">          Trigraph:       ??(  ??)  ??&lt;  ??&gt;  ??=  ??/  ??'  ??!  ??-
          Replacement:      [    ]    {    }    #    \    ^    |    ~
          </pre>

     <br><dt><code>-remap</code>
     <dd>Enable special code to work around file systems which only permit very
short file names, such as MS-DOS.

     <dt><code>--help</code>
     <dd><dt><code>--target-help</code>
     <dd>Print text describing all the command line options instead of
preprocessing anything.

     <br><dt><code>-v</code>
     <dd>Verbose mode.  Print out GNU CPP's version number at the beginning of
execution, and report the final form of the include path.

     <br><dt><code>-H</code>
     <dd>Print the name of each header file used, in addition to other normal
activities.  Each name is indented to show how deep in the
<code>#include</code> stack it is.  Precompiled header files are also
printed, even if they are found to be invalid; an invalid precompiled
header file is printed with <code>...x</code> and a valid one with <code>...!</code> .

     <br><dt><code>-version</code>
     <dd><dt><code>--version</code>
     <dd>Print out GNU CPP's version number.  With one dash, proceed to
preprocess as normal.  With two dashes, exit immediately. 
</dl>

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