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📁 自己收集的linux入门到学懂高级编程书集包括linux程序设计第三版
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<html lang="en"><head><title>Using the GNU Compiler Collection (GCC)</title><meta http-equiv="Content-Type" content="text/html"><meta name="description" content="Using the GNU Compiler Collection (GCC)"><meta name="generator" content="makeinfo 4.6"><!--Copyright &copy; 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,1999, 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc.   <p>Permission is granted to copy, distribute and/or modify this documentunder the terms of the GNU Free Documentation License, Version 1.2 orany later version published by the Free Software Foundation; with theInvariant Sections being "GNU General Public License" and "FundingFree Software", the Front-Cover texts being (a) (see below), and withthe Back-Cover Texts being (b) (see below).  A copy of the license isincluded in the section entitled "GNU Free Documentation License".   <p>(a) The FSF's Front-Cover Text is:   <p>A GNU Manual   <p>(b) The FSF's Back-Cover Text is:   <p>You have freedom to copy and modify this GNU Manual, like GNU     software.  Copies published by the Free Software Foundation raise     funds for GNU development.--><meta http-equiv="Content-Style-Type" content="text/css"><style type="text/css"><!--  pre.display { font-family:inherit }  pre.format  { font-family:inherit }  pre.smalldisplay { font-family:inherit; font-size:smaller }  pre.smallformat  { font-family:inherit; font-size:smaller }  pre.smallexample { font-size:smaller }  pre.smalllisp    { font-size:smaller }--></style></head><body><div class="node"><p>Node:&nbsp;<a name="Directory%20Options">Directory Options</a>,Next:&nbsp;<a rel="next" accesskey="n" href="Spec-Files.html#Spec%20Files">Spec Files</a>,Previous:&nbsp;<a rel="previous" accesskey="p" href="Link-Options.html#Link%20Options">Link Options</a>,Up:&nbsp;<a rel="up" accesskey="u" href="Invoking-GCC.html#Invoking%20GCC">Invoking GCC</a><hr><br></div><h3 class="section">Options for Directory Search</h3><p>These options specify directories to search for header files, forlibraries and for parts of the compiler:     <dl><dt><code>-I</code><var>dir</var><code></code>     <dd>Add the directory <var>dir</var> to the head of the list of directories to besearched for header files.  This can be used to override a system headerfile, substituting your own version, since these directories aresearched before the system header file directories.  However, you shouldnot use this option to add directories that contain vendor-suppliedsystem header files (use <code>-isystem</code> for that).  If you use more thanone <code>-I</code> option, the directories are scanned in left-to-rightorder; the standard system directories come after.     <p>If a standard system include directory, or a directory specified with<code>-isystem</code>, is also specified with <code>-I</code>, the <code>-I</code>option will be ignored.  The directory will still be searched but as asystem directory at its normal position in the system include chain. This is to ensure that GCC's procedure to fix buggy system headers andthe ordering for the include_next directive are not inadvertently changed. If you really need to change the search order for system directories,use the <code>-nostdinc</code> and/or <code>-isystem</code> options.     <br><dt><code>-I-</code>     <dd>Any directories you specify with <code>-I</code> options before the <code>-I-</code>option are searched only for the case of <code>#include "</code><var>file</var><code>"</code>;they are not searched for <code>#include &lt;</code><var>file</var><code>&gt;</code>.     <p>If additional directories are specified with <code>-I</code> options afterthe <code>-I-</code>, these directories are searched for all <code>#include</code>directives.  (Ordinarily <em>all</em> <code>-I</code> directories are usedthis way.)     <p>In addition, the <code>-I-</code> option inhibits the use of the currentdirectory (where the current input file came from) as the first searchdirectory for <code>#include "</code><var>file</var><code>"</code>.  There is no way tooverride this effect of <code>-I-</code>.  With <code>-I.</code> you can specifysearching the directory which was current when the compiler wasinvoked.  That is not exactly the same as what the preprocessor doesby default, but it is often satisfactory.     <p><code>-I-</code> does not inhibit the use of the standard system directoriesfor header files.  Thus, <code>-I-</code> and <code>-nostdinc</code> areindependent.     <br><dt><code>-L</code><var>dir</var><code></code>     <dd>Add directory <var>dir</var> to the list of directories to be searchedfor <code>-l</code>.     <br><dt><code>-B</code><var>prefix</var><code></code>     <dd>This option specifies where to find the executables, libraries,include files, and data files of the compiler itself.     <p>The compiler driver program runs one or more of the subprograms<code>cpp</code>, <code>cc1</code>, <code>as</code> and <code>ld</code>.  It tries<var>prefix</var> as a prefix for each program it tries to run, both with andwithout <code></code><var>machine</var><code>/</code><var>version</var><code>/</code> (see <a href="Target-Options.html#Target%20Options">Target Options</a>).     <p>For each subprogram to be run, the compiler driver first tries the<code>-B</code> prefix, if any.  If that name is not found, or if <code>-B</code>was not specified, the driver tries two standard prefixes, which are<code>/usr/lib/gcc/</code> and <code>/usr/local/lib/gcc/</code>.  If neither ofthose results in a file name that is found, the unmodified programname is searched for using the directories specified in your<code>PATH</code> environment variable.     <p>The compiler will check to see if the path provided by the <code>-B</code>refers to a directory, and if necessary it will add a directoryseparator character at the end of the path.     <p><code>-B</code> prefixes that effectively specify directory names also applyto libraries in the linker, because the compiler translates theseoptions into <code>-L</code> options for the linker.  They also apply toincludes files in the preprocessor, because the compiler translates theseoptions into <code>-isystem</code> options for the preprocessor.  In this case,the compiler appends <code>include</code> to the prefix.     <p>The run-time support file <code>libgcc.a</code> can also be searched for usingthe <code>-B</code> prefix, if needed.  If it is not found there, the twostandard prefixes above are tried, and that is all.  The file is leftout of the link if it is not found by those means.     <p>Another way to specify a prefix much like the <code>-B</code> prefix is to usethe environment variable <code>GCC_EXEC_PREFIX</code>.  See <a href="Environment-Variables.html#Environment%20Variables">Environment Variables</a>.     <p>As a special kludge, if the path provided by <code>-B</code> is<code>[dir/]stage</code><var>N</var><code>/</code>, where <var>N</var> is a number in the range 0 to9, then it will be replaced by <code>[dir/]include</code>.  This is to helpwith boot-strapping the compiler.     <br><dt><code>-specs=</code><var>file</var><code></code>     <dd>Process <var>file</var> after the compiler reads in the standard <code>specs</code>file, in order to override the defaults that the <code>gcc</code> driverprogram uses when determining what switches to pass to <code>cc1</code>,<code>cc1plus</code>, <code>as</code>, <code>ld</code>, etc.  More than one<code>-specs=</code><var>file</var><code></code> can be specified on the command line, and theyare processed in order, from left to right. </dl>   </body></html>
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