1 @c Copyright (C) 2000-2016 Free Software Foundation, Inc.
2 @c This is part of the GCC manual.
3 @c For copying conditions, see the file gcc.texi.
6 @chapter Language Standards Supported by GCC
8 For each language compiled by GCC for which there is a standard, GCC
9 attempts to follow one or more versions of that standard, possibly
10 with some exceptions, and possibly with some extensions.
15 @cindex ANSI C standard
19 @cindex ANSI X3.159-1989
21 @cindex ISO C standard
39 @cindex Technical Corrigenda
41 @cindex Technical Corrigendum 1
43 @cindex Technical Corrigendum 2
45 @cindex Technical Corrigendum 3
47 @cindex freestanding implementation
48 @cindex freestanding environment
49 @cindex hosted implementation
50 @cindex hosted environment
51 @findex __STDC_HOSTED__
56 @opindex pedantic-errors
57 The original ANSI C standard (X3.159-1989) was ratified in 1989 and
58 published in 1990. This standard was ratified as an ISO standard
59 (ISO/IEC 9899:1990) later in 1990. There were no technical
60 differences between these publications, although the sections of the
61 ANSI standard were renumbered and became clauses in the ISO standard.
63 standard, but not the ISO standard, also came with a Rationale
65 This standard, in both its forms, is commonly known as @dfn{C89}, or
66 occasionally as @dfn{C90}, from the dates of ratification.
67 To select this standard in GCC, use one of the options
68 @option{-ansi}, @option{-std=c90} or @option{-std=iso9899:1990}; to obtain
69 all the diagnostics required by the standard, you should also specify
70 @option{-pedantic} (or @option{-pedantic-errors} if you want them to be
71 errors rather than warnings). @xref{C Dialect Options,,Options
72 Controlling C Dialect}.
74 Errors in the 1990 ISO C standard were corrected in two Technical
75 Corrigenda published in 1994 and 1996. GCC does not support the
78 An amendment to the 1990 standard was published in 1995. This
79 amendment added digraphs and @code{__STDC_VERSION__} to the language,
80 but otherwise concerned the library. This amendment is commonly known
81 as @dfn{AMD1}; the amended standard is sometimes known as @dfn{C94} or
82 @dfn{C95}. To select this standard in GCC, use the option
83 @option{-std=iso9899:199409} (with, as for other standard versions,
84 @option{-pedantic} to receive all required diagnostics).
86 A new edition of the ISO C standard was published in 1999 as ISO/IEC
87 9899:1999, and is commonly known as @dfn{C99}. (While in
88 development, drafts of this standard version were referred to as
89 @dfn{C9X}.) GCC has substantially
90 complete 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}.
94 Errors in the 1999 ISO C standard were corrected in three Technical
95 Corrigenda published in 2001, 2004 and 2007. GCC does not support the
98 A fourth version of the C standard, known as @dfn{C11}, was published
99 in 2011 as ISO/IEC 9899:2011. (While in development, drafts of this
100 standard version were referred to as @dfn{C1X}.)
101 GCC has substantially complete support
102 for this standard, enabled with @option{-std=c11} or
103 @option{-std=iso9899:2011}.
105 By default, GCC provides some extensions to the C language that, on
106 rare occasions conflict with the C standard. @xref{C
107 Extensions,,Extensions to the C Language Family}.
108 Some features that are part of the C99 standard
109 are accepted as extensions in C90 mode, and some features that are part
110 of the C11 standard are accepted as extensions in C90 and C99 modes.
112 @option{-std} options listed above disables these extensions where
113 they conflict with the C standard version selected. You may also
114 select an extended version of the C language explicitly with
115 @option{-std=gnu90} (for C90 with GNU extensions), @option{-std=gnu99}
116 (for C99 with GNU extensions) or @option{-std=gnu11} (for C11 with GNU
119 The default, if no C language dialect options are given,
120 is @option{-std=gnu11}.
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.
133 The standard also defines two environments for programs, a
134 @dfn{freestanding environment}, required of all implementations and
135 which may not have library facilities beyond those required of
136 freestanding implementations, where the handling of program startup
137 and termination are implementation-defined; and a @dfn{hosted
138 environment}, which is not required, in which all the library
139 facilities are provided and startup is through a function @code{int
140 main (void)} or @code{int main (int, char *[])}. An OS kernel is an example
141 of a program running in a freestanding environment;
142 a program using the facilities of an
143 operating system is an example of a program running in a hosted environment.
145 @opindex ffreestanding
146 GCC aims towards being usable as a conforming freestanding
147 implementation, or as the compiler for a conforming hosted
148 implementation. By default, it acts as the compiler for a hosted
149 implementation, defining @code{__STDC_HOSTED__} as @code{1} and
150 presuming that when the names of ISO C functions are used, they have
151 the semantics defined in the standard. To make it act as a conforming
152 freestanding implementation for a freestanding environment, use the
153 option @option{-ffreestanding}; it then defines
154 @code{__STDC_HOSTED__} to @code{0} and does not make assumptions about the
155 meanings of function names from the standard library, with exceptions
156 noted below. To build an OS kernel, you may well still need to make
157 your own arrangements for linking and startup.
158 @xref{C Dialect Options,,Options Controlling C Dialect}.
160 GCC does not provide the library facilities required only of hosted
161 implementations, nor yet all the facilities required by C99 of
162 freestanding implementations on all platforms.
163 To use the facilities of a hosted
164 environment, you need to find them elsewhere (for example, in the
165 GNU C library). @xref{Standard Libraries,,Standard Libraries}.
167 Most of the compiler support routines used by GCC are present in
168 @file{libgcc}, but there are a few exceptions. GCC requires the
169 freestanding environment provide @code{memcpy}, @code{memmove},
170 @code{memset} and @code{memcmp}.
171 Finally, if @code{__builtin_trap} is used, and the target does
172 not implement the @code{trap} pattern, then GCC emits a call
175 For references to Technical Corrigenda, Rationale documents and
176 information concerning the history of C that is available online, see
177 @uref{http://gcc.gnu.org/readings.html}
179 @section C++ Language
181 GCC supports the original ISO C++ standard published in 1998,
182 and the 2011 and 2014 revisions.
184 The original ISO C++ standard was published as the ISO standard (ISO/IEC
185 14882:1998) and amended by a Technical Corrigenda published in 2003
186 (ISO/IEC 14882:2003). These standards are referred to as C++98 and
187 C++03, respectively. GCC implements the majority of C++98 (@code{export}
188 is a notable exception) and most of the changes in C++03. To select
189 this standard in GCC, use one of the options @option{-ansi},
190 @option{-std=c++98}, or @option{-std=c++03}; to obtain all the diagnostics
191 required by the standard, you should also specify @option{-pedantic} (or
192 @option{-pedantic-errors} if you want them to be errors rather than
195 A revised ISO C++ standard was published in 2011 as ISO/IEC
196 14882:2011, and is referred to as C++11; before its publication it was
197 commonly referred to as C++0x. C++11 contains several changes to the
198 C++ language, all of which have been implemented in GCC@. For details
199 see @uref{https://gcc.gnu.org/projects/@/cxx0x.html}.
200 To select this standard in GCC, use the option @option{-std=c++11}.
202 Another revised ISO C++ standard was published in 2014 as ISO/IEC
203 14882:2014, and is referred to as C++14; before its publication it was
204 sometimes referred to as C++1y. C++14 contains several further
205 changes to the C++ language, all of which have been implemented in GCC@.
206 For details see @uref{https://gcc.gnu.org/projects/@/cxx1y.html}.
207 To select this standard in GCC, use the option @option{-std=c++14}.
209 GCC also supports the C++ Concepts Technical Specification,
210 ISO/IEC TS 19217:2015, which allows constraints to be defined for templates,
211 allowing template arguments to be checked and for templates to be
212 overloaded or specialized based on the constraints. Support for C++ Concepts
213 is included in an experimental C++1z mode that corresponds to the next
214 revision of the ISO C++ standard, expected to be published in 2017. To enable
215 C++1z support in GCC, use the option @option{-std=c++17} or
218 More information about the C++ standards is available on the ISO C++
219 committee's web site at @uref{http://www.open-std.org/@/jtc1/@/sc22/@/wg21/}.
221 To obtain all the diagnostics required by any of the standard versions
222 described above you should specify @option{-pedantic}
223 or @option{-pedantic-errors}, otherwise GCC will allow some non-ISO C++
224 features as extensions. @xref{Warning Options}.
226 By default, GCC also provides some additional extensions to the C++ language
227 that on rare occasions conflict with the C++ standard. @xref{C++
228 Dialect Options,Options Controlling C++ Dialect}. Use of the
229 @option{-std} options listed above disables these extensions where they
230 they conflict with the C++ standard version selected. You may also
231 select an extended version of the C++ language explicitly with
232 @option{-std=gnu++98} (for C++98 with GNU extensions), or
233 @option{-std=gnu++11} (for C++11 with GNU extensions), or
234 @option{-std=gnu++14} (for C++14 with GNU extensions), or
235 @option{-std=gnu++1z} (for C++1z with GNU extensions).
238 no C++ language dialect options are given, is @option{-std=gnu++14}.
240 @section Objective-C and Objective-C++ Languages
242 @cindex Objective-C++
244 GCC supports ``traditional'' Objective-C (also known as ``Objective-C
245 1.0'') and contains support for the Objective-C exception and
246 synchronization syntax. It has also support for a number of
247 ``Objective-C 2.0'' language extensions, including properties, fast
248 enumeration (only for Objective-C), method attributes and the
249 @@optional and @@required keywords in protocols. GCC supports
250 Objective-C++ and features available in Objective-C are also available
253 GCC by default uses the GNU Objective-C runtime library, which is part
254 of GCC and is not the same as the Apple/NeXT Objective-C runtime
255 library used on Apple systems. There are a number of differences
256 documented in this manual. The options @option{-fgnu-runtime} and
257 @option{-fnext-runtime} allow you to switch between producing output
258 that works with the GNU Objective-C runtime library and output that
259 works with the Apple/NeXT Objective-C runtime library.
261 There is no formal written standard for Objective-C or Objective-C++@.
262 The authoritative manual on traditional Objective-C (1.0) is
263 ``Object-Oriented Programming and the Objective-C Language'':
266 @uref{http://www.gnustep.org/@/resources/@/documentation/@/ObjectivCBook.pdf}
267 is the original NeXTstep document;
269 @uref{http://objc.toodarkpark.net}
270 is the same document in another format.
273 The Objective-C exception and synchronization syntax (that is, the
274 keywords @code{@@try}, @code{@@throw}, @code{@@catch},
275 @code{@@finally} and @code{@@synchronized}) is
276 supported by GCC and is enabled with the option
277 @option{-fobjc-exceptions}. The syntax is briefly documented in this
278 manual and in the Objective-C 2.0 manuals from Apple.
280 The Objective-C 2.0 language extensions and features are automatically
281 enabled; they include properties (via the @code{@@property},
282 @code{@@synthesize} and
283 @code{@@dynamic keywords}), fast enumeration (not available in
284 Objective-C++), attributes for methods (such as @code{deprecated},
285 @code{noreturn}, @code{sentinel}, @code{format}),
286 the @code{unused} attribute for method arguments, the
287 @code{@@package} keyword for instance variables and the @code{@@optional} and
288 @code{@@required} keywords in protocols. You can disable all these
289 Objective-C 2.0 language extensions with the option
290 @option{-fobjc-std=objc1}, which causes the compiler to recognize the
291 same Objective-C language syntax recognized by GCC 4.0, and to produce
292 an error if one of the new features is used.
294 GCC has currently no support for non-fragile instance variables.
296 The authoritative manual on Objective-C 2.0 is available from Apple:
299 @uref{https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/Introduction/Introduction.html}
302 For more information concerning the history of Objective-C that is
303 available online, see @uref{http://gcc.gnu.org/readings.html}
307 As of the GCC 4.7.1 release, GCC supports the Go 1 language standard,
308 described at @uref{http://golang.org/doc/go1.html}.
310 @section References for Other Languages
312 @xref{Top, GNAT Reference Manual, About This Guide, gnat_rm,
313 GNAT Reference Manual}, for information on standard
314 conformance and compatibility of the Ada compiler.
316 @xref{Standards,,Standards, gfortran, The GNU Fortran Compiler}, for details
317 of standards supported by GNU Fortran.
319 @xref{Compatibility,,Compatibility with the Java Platform, gcj, GNU gcj},
320 for details of compatibility between @command{gcj} and the Java Platform.