1 @c Copyright (C) 2000, 2001, 2002, 2004, 2006, 2007, 2008, 2010
2 @c Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
7 @chapter Language Standards Supported by GCC
9 For each language compiled by GCC for which there is a standard, GCC
10 attempts to follow one or more versions of that standard, possibly
11 with some exceptions, and possibly with some extensions.
16 @cindex ANSI C standard
20 @cindex ANSI X3.159-1989
22 @cindex ISO C standard
40 @cindex Technical Corrigenda
42 @cindex Technical Corrigendum 1
44 @cindex Technical Corrigendum 2
46 @cindex Technical Corrigendum 3
48 @cindex freestanding implementation
49 @cindex freestanding environment
50 @cindex hosted implementation
51 @cindex hosted environment
52 @findex __STDC_HOSTED__
54 GCC supports three versions of the C standard, although support for
55 the most recent version is not yet complete.
60 @opindex pedantic-errors
61 The original ANSI C standard (X3.159-1989) was ratified in 1989 and
62 published in 1990. This standard was ratified as an ISO standard
63 (ISO/IEC 9899:1990) later in 1990. There were no technical
64 differences between these publications, although the sections of the
65 ANSI standard were renumbered and became clauses in the ISO standard.
66 This standard, in both its forms, is commonly known as @dfn{C89}, or
67 occasionally as @dfn{C90}, from the dates of ratification. The ANSI
68 standard, but not the ISO standard, also came with a Rationale
69 document. To select this standard in GCC, use one of the options
70 @option{-ansi}, @option{-std=c90} or @option{-std=iso9899:1990}; to obtain
71 all the diagnostics required by the standard, you should also specify
72 @option{-pedantic} (or @option{-pedantic-errors} if you want them to be
73 errors rather than warnings). @xref{C Dialect Options,,Options
74 Controlling C Dialect}.
76 Errors in the 1990 ISO C standard were corrected in two Technical
77 Corrigenda published in 1994 and 1996. GCC does not support the
80 An amendment to the 1990 standard was published in 1995. This
81 amendment added digraphs and @code{__STDC_VERSION__} to the language,
82 but otherwise concerned the library. This amendment is commonly known
83 as @dfn{AMD1}; the amended standard is sometimes known as @dfn{C94} or
84 @dfn{C95}. To select this standard in GCC, use the option
85 @option{-std=iso9899:199409} (with, as for other standard versions,
86 @option{-pedantic} to receive all required diagnostics).
88 A new edition of the ISO C standard was published in 1999 as ISO/IEC
89 9899:1999, and is commonly known as @dfn{C99}. GCC has incomplete
90 support for this standard version; see
91 @uref{http://gcc.gnu.org/c99status.html} for details. To select this
92 standard, use @option{-std=c99} or @option{-std=iso9899:1999}. (While in
93 development, drafts of this standard version were referred to as
96 Errors in the 1999 ISO C standard were corrected in three Technical
97 Corrigenda published in 2001, 2004 and 2007. GCC does not support the
100 A fourth version of the C standard, known as @dfn{C11}, was published
101 in 2011 as ISO/IEC 9899:2011. GCC has limited incomplete support for
102 parts of this standard, enabled with @option{-std=c11} or
103 @option{-std=iso9899:2011}. (While in development, drafts of this
104 standard version were referred to as @dfn{C1X}.)
106 By default, GCC provides some extensions to the C language that on
107 rare occasions conflict with the C standard. @xref{C
108 Extensions,,Extensions to the C Language Family}. Use of the
109 @option{-std} options listed above will disable these extensions where
110 they conflict with the C standard version selected. You may also
111 select an extended version of the C language explicitly with
112 @option{-std=gnu90} (for C90 with GNU extensions), @option{-std=gnu99}
113 (for C99 with GNU extensions) or @option{-std=gnu11} (for C11 with GNU
114 extensions). The default, if no C language dialect
115 options are given, is @option{-std=gnu90}; this will change to
116 @option{-std=gnu99} or @option{-std=gnu11} in some future release when
117 the C99 or C11 support is
118 complete. Some features that are part of the C99 standard are
119 accepted as extensions in C90 mode, and some features that are part of
120 the C11 standard are accepted as extensions in C90 and C99 modes.
122 The ISO C standard defines (in clause 4) two classes of conforming
123 implementation. A @dfn{conforming hosted implementation} supports the
124 whole standard including all the library facilities; a @dfn{conforming
125 freestanding implementation} is only required to provide certain
126 library facilities: those in @code{<float.h>}, @code{<limits.h>},
127 @code{<stdarg.h>}, and @code{<stddef.h>}; since AMD1, also those in
128 @code{<iso646.h>}; since C99, also those in @code{<stdbool.h>} and
129 @code{<stdint.h>}; and since C11, also those in @code{<stdalign.h>}
130 and @code{<stdnoreturn.h>}. In addition, complex types, added in C99, are not
131 required for freestanding implementations. The standard also defines
132 two environments for programs, a @dfn{freestanding environment},
133 required of all implementations and which may not have library
134 facilities beyond those required of freestanding implementations,
135 where the handling of program startup and termination are
136 implementation-defined, and a @dfn{hosted environment}, which is not
137 required, in which all the library facilities are provided and startup
138 is through a function @code{int main (void)} or @code{int main (int,
139 char *[])}. An OS kernel would be a freestanding environment; a
140 program using the facilities of an operating system would normally be
141 in a hosted implementation.
143 @opindex ffreestanding
144 GCC aims towards being usable as a conforming freestanding
145 implementation, or as the compiler for a conforming hosted
146 implementation. By default, it will act as the compiler for a hosted
147 implementation, defining @code{__STDC_HOSTED__} as @code{1} and
148 presuming that when the names of ISO C functions are used, they have
149 the semantics defined in the standard. To make it act as a conforming
150 freestanding implementation for a freestanding environment, use the
151 option @option{-ffreestanding}; it will then define
152 @code{__STDC_HOSTED__} to @code{0} and not make assumptions about the
153 meanings of function names from the standard library, with exceptions
154 noted below. To build an OS kernel, you may well still need to make
155 your own arrangements for linking and startup.
156 @xref{C Dialect Options,,Options Controlling C Dialect}.
158 GCC does not provide the library facilities required only of hosted
159 implementations, nor yet all the facilities required by C99 of
160 freestanding implementations; to use the facilities of a hosted
161 environment, you will need to find them elsewhere (for example, in the
162 GNU C library). @xref{Standard Libraries,,Standard Libraries}.
164 Most of the compiler support routines used by GCC are present in
165 @file{libgcc}, but there are a few exceptions. GCC requires the
166 freestanding environment provide @code{memcpy}, @code{memmove},
167 @code{memset} and @code{memcmp}.
168 Finally, if @code{__builtin_trap} is used, and the target does
169 not implement the @code{trap} pattern, then GCC will emit a call
172 For references to Technical Corrigenda, Rationale documents and
173 information concerning the history of C that is available online, see
174 @uref{http://gcc.gnu.org/readings.html}
176 @section C++ language
178 GCC supports the ISO C++ standard (1998) and contains experimental
179 support for the upcoming ISO C++ standard (200x).
181 The original ISO C++ standard was published as the ISO standard (ISO/IEC
182 14882:1998) and amended by a Technical Corrigenda published in 2003
183 (ISO/IEC 14882:2003). These standards are referred to as C++98 and
184 C++03, respectively. GCC implements the majority of C++98 (@code{export}
185 is a notable exception) and most of the changes in C++03. To select
186 this standard in GCC, use one of the options @option{-ansi} or
187 @option{-std=c++98}; to obtain all the diagnostics required by the
188 standard, you should also specify @option{-pedantic} (or
189 @option{-pedantic-errors} if you want them to be errors rather than
192 The ISO C++ committee is working on a new ISO C++ standard, dubbed
193 C++0x, that is intended to be published by 2009. C++0x contains several
194 changes to the C++ language, some of which have been implemented in an
195 experimental C++0x mode in GCC@. The C++0x mode in GCC tracks the draft
196 working paper for the C++0x standard; the latest working paper is
197 available on the ISO C++ committee's web site at
198 @uref{http://www.open-std.org/@/jtc1/@/sc22/@/wg21/}. For information
199 regarding the C++0x features available in the experimental C++0x mode,
200 see @uref{http://gcc.gnu.org/projects/@/cxx0x.html}. To select this
201 standard in GCC, use the option @option{-std=c++0x}; to obtain all the
202 diagnostics required by the standard, you should also specify
203 @option{-pedantic} (or @option{-pedantic-errors} if you want them to be
204 errors rather than warnings).
206 By default, GCC provides some extensions to the C++ language; @xref{C++
207 Dialect Options,Options Controlling C++ Dialect}. Use of the
208 @option{-std} option listed above will disable these extensions. You
209 may also select an extended version of the C++ language explicitly with
210 @option{-std=gnu++98} (for C++98 with GNU extensions) or
211 @option{-std=gnu++0x} (for C++0x with GNU extensions). The default, if
212 no C++ language dialect options are given, is @option{-std=gnu++98}.
214 @section Objective-C and Objective-C++ languages
216 @cindex Objective-C++
218 GCC supports ``traditional'' Objective-C (also known as ``Objective-C
219 1.0'') and contains support for the Objective-C exception and
220 synchronization syntax. It has also support for a number of
221 ``Objective-C 2.0'' language extensions, including properties, fast
222 enumeration (only for Objective-C), method attributes and the
223 @@optional and @@required keywords in protocols. GCC supports
224 Objective-C++ and features available in Objective-C are also available
227 GCC by default uses the GNU Objective-C runtime library, which is part
228 of GCC and is not the same as the Apple/NeXT Objective-C runtime
229 library used on Apple systems. There are a number of differences
230 documented in this manual. The options @option{-fgnu-runtime} and
231 @option{-fnext-runtime} allow you to switch between producing output
232 that works with the GNU Objective-C runtime library and output that
233 works with the Apple/NeXT Objective-C runtime library.
235 There is no formal written standard for Objective-C or Objective-C++@.
236 The authoritative manual on traditional Objective-C (1.0) is
237 ``Object-Oriented Programming and the Objective-C Language'',
238 available at a number of web sites:
241 @uref{http://www.gnustep.org/@/resources/@/documentation/@/ObjectivCBook.pdf}
242 is the original NeXTstep document;
244 @uref{http://objc.toodarkpark.net}
245 is the same document in another format;
247 @uref{http://developer.apple.com/@/mac/@/library/@/documentation/@/Cocoa/@/Conceptual/@/ObjectiveC/}
248 has an updated version but make sure you search for ``Object Oriented Programming and the Objective-C Programming Language 1.0'',
249 not documentation on the newer ``Objective-C 2.0'' language
252 The Objective-C exception and synchronization syntax (that is, the
253 keywords @@try, @@throw, @@catch, @@finally and @@synchronized) is
254 supported by GCC and is enabled with the option
255 @option{-fobjc-exceptions}. The syntax is briefly documented in this
256 manual and in the Objective-C 2.0 manuals from Apple.
258 The Objective-C 2.0 language extensions and features are automatically
259 enabled; they include properties (via the @@property, @@synthesize and
260 @@dynamic keywords), fast enumeration (not available in
261 Objective-C++), attributes for methods (such as deprecated, noreturn,
262 sentinel, format), the unused attribute for method arguments, the
263 @@package keyword for instance variables and the @@optional and
264 @@required keywords in protocols. You can disable all these
265 Objective-C 2.0 language extensions with the option
266 @option{-fobjc-std=objc1}, which causes the compiler to recognize the
267 same Objective-C language syntax recognized by GCC 4.0, and to produce
268 an error if one of the new features is used.
270 GCC has currently no support for non-fragile instance variables.
272 The authoritative manual on Objective-C 2.0 is available from Apple:
275 @uref{http://developer.apple.com/@/mac/@/library/@/documentation/@/Cocoa/@/Conceptual/@/ObjectiveC/}
278 For more information concerning the history of Objective-C that is
279 available online, see @uref{http://gcc.gnu.org/readings.html}
283 The Go language continues to evolve as of this writing; see the
284 @uref{http://golang.org/@/doc/@/go_spec.html, current language
285 specifications}. At present there are no specific versions of Go, and
286 there is no way to describe the language supported by GCC in terms of
287 a specific version. In general GCC tracks the evolving specification
288 closely, and any given release will support the language as of the
289 date that the release was frozen.
291 @section References for other languages
293 @xref{Top, GNAT Reference Manual, About This Guide, gnat_rm,
294 GNAT Reference Manual}, for information on standard
295 conformance and compatibility of the Ada compiler.
297 @xref{Standards,,Standards, gfortran, The GNU Fortran Compiler}, for details
298 of standards supported by GNU Fortran.
300 @xref{Compatibility,,Compatibility with the Java Platform, gcj, GNU gcj},
301 for details of compatibility between @command{gcj} and the Java Platform.