📄 c-dialect-options.html

📁 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
💻 HTML
字号:
<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="C%20Dialect%20Options">C Dialect Options</a>,Next:&nbsp;<a rel="next" accesskey="n" href="C---Dialect-Options.html#C++%20Dialect%20Options">C++ Dialect Options</a>,Previous:&nbsp;<a rel="previous" accesskey="p" href="Invoking-G--.html#Invoking%20G++">Invoking G++</a>,Up:&nbsp;<a rel="up" accesskey="u" href="Invoking-GCC.html#Invoking%20GCC">Invoking GCC</a><hr><br></div><h3 class="section">Options Controlling C Dialect</h3><p>The following options control the dialect of C (or languages derivedfrom C, such as C++ and Objective-C) that the compiler accepts:     <dl><dt><code>-ansi</code>     <dd>In C mode, support all ISO C90 programs.  In C++ mode,remove GNU extensions that conflict with ISO C++.     <p>This turns off certain features of GCC that are incompatible with ISOC90 (when compiling C code), or of standard C++ (when compiling C++ code),such as the <code>asm</code> and <code>typeof</code> keywords, andpredefined macros such as <code>unix</code> and <code>vax</code> that identify thetype of system you are using.  It also enables the undesirable andrarely used ISO trigraph feature.  For the C compiler,it disables recognition of C++ style <code>//</code> comments as well asthe <code>inline</code> keyword.     <p>The alternate keywords <code>__asm__</code>, <code>__extension__</code>,<code>__inline__</code> and <code>__typeof__</code> continue to work despite<code>-ansi</code>.  You would not want to use them in an ISO C program, ofcourse, but it is useful to put them in header files that might be includedin compilations done with <code>-ansi</code>.  Alternate predefined macrossuch as <code>__unix__</code> and <code>__vax__</code> are also available, with orwithout <code>-ansi</code>.     <p>The <code>-ansi</code> option does not cause non-ISO programs to berejected gratuitously.  For that, <code>-pedantic</code> is required inaddition to <code>-ansi</code>.  See <a href="Warning-Options.html#Warning%20Options">Warning Options</a>.     <p>The macro <code>__STRICT_ANSI__</code> is predefined when the <code>-ansi</code>option is used.  Some header files may notice this macro and refrainfrom declaring certain functions or defining certain macros that theISO standard doesn't call for; this is to avoid interfering with anyprograms that might use these names for other things.     <p>Functions which would normally be built in but do not have semanticsdefined by ISO C (such as <code>alloca</code> and <code>ffs</code>) are not built-infunctions with <code>-ansi</code> is used.  See <a href="Other-Builtins.html#Other%20Builtins">Other built-in functions provided by GCC</a>, for details of the functionsaffected.     <br><dt><code>-std=</code>     <dd>Determine the language standard.  This option is currently onlysupported when compiling C or C++.  A value for this option must beprovided; possible values are          <dl><dt><code>c89</code>          <dd><dt><code>iso9899:1990</code>          <dd>ISO C90 (same as <code>-ansi</code>).          <br><dt><code>iso9899:199409</code>          <dd>ISO C90 as modified in amendment 1.          <br><dt><code>c99</code>          <dd><dt><code>c9x</code>          <dd><dt><code>iso9899:1999</code>          <dd><dt><code>iso9899:199x</code>          <dd>ISO C99.  Note that this standard is not yet fully supported; see<a href="http://gcc.gnu.org/c99status.html">http://gcc.gnu.org/c99status.html</a> for more information.  Thenames <code>c9x</code> and <code>iso9899:199x</code> are deprecated.          <br><dt><code>gnu89</code>          <dd>Default, ISO C90 plus GNU extensions (including some C99 features).          <br><dt><code>gnu99</code>          <dd><dt><code>gnu9x</code>          <dd>ISO C99 plus GNU extensions.  When ISO C99 is fully implemented in GCC,this will become the default.  The name <code>gnu9x</code> is deprecated.          <br><dt><code>c++98</code>          <dd>The 1998 ISO C++ standard plus amendments.          <br><dt><code>gnu++98</code>          <dd>The same as <code>-std=c++98</code> plus GNU extensions.  This is thedefault for C++ code. </dl>     <p>Even when this option is not specified, you can still use some of thefeatures of newer standards in so far as they do not conflict withprevious C standards.  For example, you may use <code>__restrict__</code> evenwhen <code>-std=c99</code> is not specified.     <p>The <code>-std</code> options specifying some version of ISO C have the sameeffects as <code>-ansi</code>, except that features that were not in ISO C90but are in the specified version (for example, <code>//</code> comments andthe <code>inline</code> keyword in ISO C99) are not disabled.     <p>See <a href="Standards.html#Standards">Language Standards Supported by GCC</a>, for details ofthese standard versions.     <br><dt><code>-aux-info </code><var>filename</var><code></code>     <dd>Output to the given filename prototyped declarations for all functionsdeclared and/or defined in a translation unit, including those in headerfiles.  This option is silently ignored in any language other than C.     <p>Besides declarations, the file indicates, in comments, the origin ofeach declaration (source file and line), whether the declaration wasimplicit, prototyped or unprototyped (<code>I</code>, <code>N</code> for new or<code>O</code> for old, respectively, in the first character after the linenumber and the colon), and whether it came from a declaration or adefinition (<code>C</code> or <code>F</code>, respectively, in the followingcharacter).  In the case of function definitions, a K&amp;R-style list ofarguments followed by their declarations is also provided, insidecomments, after the declaration.     <br><dt><code>-fno-asm</code>     <dd>Do not recognize <code>asm</code>, <code>inline</code> or <code>typeof</code> as akeyword, so that code can use these words as identifiers.  You can usethe keywords <code>__asm__</code>, <code>__inline__</code> and <code>__typeof__</code>instead.  <code>-ansi</code> implies <code>-fno-asm</code>.     <p>In C++, this switch only affects the <code>typeof</code> keyword, since<code>asm</code> and <code>inline</code> are standard keywords.  You may want touse the <code>-fno-gnu-keywords</code> flag instead, which has the sameeffect.  In C99 mode (<code>-std=c99</code> or <code>-std=gnu99</code>), thisswitch only affects the <code>asm</code> and <code>typeof</code> keywords, since<code>inline</code> is a standard keyword in ISO C99.     <br><dt><code>-fno-builtin</code>     <dd><dt><code>-fno-builtin-</code><var>function</var><code></code>     <dd>Don't recognize built-in functions that do not begin with<code>__builtin_</code> as prefix.  See <a href="Other-Builtins.html#Other%20Builtins">Other built-in functions provided by GCC</a>, for details of the functions affected,including those which are not built-in functions when <code>-ansi</code> or<code>-std</code> options for strict ISO C conformance are used because theydo not have an ISO standard meaning.     <p>GCC normally generates special code to handle certain built-in functionsmore efficiently; for instance, calls to <code>alloca</code> may become singleinstructions that adjust the stack directly, and calls to <code>memcpy</code>may become inline copy loops.  The resulting code is often both smallerand faster, but since the function calls no longer appear as such, youcannot set a breakpoint on those calls, nor can you change the behaviorof the functions by linking with a different library.     <p>With the <code>-fno-builtin-</code><var>function</var><code></code> optiononly the built-in function <var>function</var> isdisabled.  <var>function</var> must not begin with <code>__builtin_</code>.  If afunction is named this is not built-in in this version of GCC, thisoption is ignored.  There is no corresponding<code>-fbuiltin-</code><var>function</var><code></code> option; if you wish to enablebuilt-in functions selectively when using <code>-fno-builtin</code> or<code>-ffreestanding</code>, you may define macros such as:     <pre class="smallexample">          #define abs(n)          __builtin_abs ((n))          #define strcpy(d, s)    __builtin_strcpy ((d), (s))          </pre>     <br><dt><code>-fhosted</code>     <dd>     <p>Assert that compilation takes place in a hosted environment.  This implies<code>-fbuiltin</code>.  A hosted environment is one in which theentire standard library is available, and in which <code>main</code> has a returntype of <code>int</code>.  Examples are nearly everything except a kernel. This is equivalent to <code>-fno-freestanding</code>.     <br><dt><code>-ffreestanding</code>     <dd>     <p>Assert that compilation takes place in a freestanding environment.  Thisimplies <code>-fno-builtin</code>.  A freestanding environmentis one in which the standard library may not exist, and program startup maynot necessarily be at <code>main</code>.  The most obvious example is an OS kernel. This is equivalent to <code>-fno-hosted</code>.     <p>See <a href="Standards.html#Standards">Language Standards Supported by GCC</a>, for details offreestanding and hosted environments.     <br><dt><code>-fms-extensions</code>     <dd>Accept some non-standard constructs used in Microsoft header files.     <br><dt><code>-trigraphs</code>     <dd>Support ISO C trigraphs.  The <code>-ansi</code> option (and <code>-std</code>options for strict ISO C conformance) implies <code>-trigraphs</code>.     <br><dt><code>-no-integrated-cpp</code>     <dd>Performs a compilation in two passes: preprocessing and compiling.  Thisoption allows a user supplied "cc1", "cc1plus", or "cc1obj" via the<code>-B</code> option. The user supplied compilation step can then add inan additional preprocessing step after normal preprocessing but beforecompiling. The default is to use the integrated cpp (internal cpp)     <p>The semantics of this option will change if "cc1", "cc1plus", and"cc1obj" are merged.     <br><dt><code>-traditional</code>     <dd><dt><code>-traditional-cpp</code>     <dd>Formerly, these options caused GCC to attempt to emulate a pre-standardC compiler.  They are now only supported with the <code>-E</code> switch. The preprocessor continues to support a pre-standard mode.  See the GNUCPP manual for details.     <br><dt><code>-fcond-mismatch</code>     <dd>Allow conditional expressions with mismatched types in the second andthird arguments.  The value of such an expression is void.  This optionis not supported for C++.     <br><dt><code>-funsigned-char</code>     <dd>Let the type <code>char</code> be unsigned, like <code>unsigned char</code>.     <p>Each kind of machine has a default for what <code>char</code> shouldbe.  It is either like <code>unsigned char</code> by default or like<code>signed char</code> by default.     <p>Ideally, a portable program should always use <code>signed char</code> or<code>unsigned char</code> when it depends on the signedness of an object. But many programs have been written to use plain <code>char</code> andexpect it to be signed, or expect it to be unsigned, depending on themachines they were written for.  This option, and its inverse, let youmake such a program work with the opposite default.     <p>The type <code>char</code> is always a distinct type from each of<code>signed char</code> or <code>unsigned char</code>, even though its behavioris always just like one of those two.     <br><dt><code>-fsigned-char</code>     <dd>Let the type <code>char</code> be signed, like <code>signed char</code>.     <p>Note that this is equivalent to <code>-fno-unsigned-char</code>, which isthe negative form of <code>-funsigned-char</code>.  Likewise, the option<code>-fno-signed-char</code> is equivalent to <code>-funsigned-char</code>.     <br><dt><code>-fsigned-bitfields</code>     <dd><dt><code>-funsigned-bitfields</code>     <dd><dt><code>-fno-signed-bitfields</code>     <dd><dt><code>-fno-unsigned-bitfields</code>     <dd>These options control whether a bit-field is signed or unsigned, when thedeclaration does not use either <code>signed</code> or <code>unsigned</code>.  Bydefault, such a bit-field is signed, because this is consistent: thebasic integer types such as <code>int</code> are signed types. </dl>   </body></html>
⌨️ 快捷键说明

复制代码 Ctrl + C
搜索代码 Ctrl + F
全屏模式 F11
切换主题 Ctrl + Shift + D
显示快捷键 ?
增大字号 Ctrl + =
减小字号 Ctrl + -