1@c Copyright (C) 2000-2015 Free Software Foundation, Inc. 2@c This is part of the GCC manual. 3@c For copying conditions, see the file gcc.texi. 4 5@node Standards 6@chapter Language Standards Supported by GCC 7 8For each language compiled by GCC for which there is a standard, GCC 9attempts to follow one or more versions of that standard, possibly 10with some exceptions, and possibly with some extensions. 11 12@section C Language 13@cindex C standard 14@cindex C standards 15@cindex ANSI C standard 16@cindex ANSI C 17@cindex ANSI C89 18@cindex C89 19@cindex ANSI X3.159-1989 20@cindex X3.159-1989 21@cindex ISO C standard 22@cindex ISO C 23@cindex ISO C90 24@cindex ISO/IEC 9899 25@cindex ISO 9899 26@cindex C90 27@cindex ISO C94 28@cindex C94 29@cindex ISO C95 30@cindex C95 31@cindex ISO C99 32@cindex C99 33@cindex ISO C9X 34@cindex C9X 35@cindex ISO C11 36@cindex C11 37@cindex ISO C1X 38@cindex C1X 39@cindex Technical Corrigenda 40@cindex TC1 41@cindex Technical Corrigendum 1 42@cindex TC2 43@cindex Technical Corrigendum 2 44@cindex TC3 45@cindex Technical Corrigendum 3 46@cindex AMD1 47@cindex freestanding implementation 48@cindex freestanding environment 49@cindex hosted implementation 50@cindex hosted environment 51@findex __STDC_HOSTED__ 52 53GCC supports three versions of the C standard, although support for 54the most recent version is not yet complete. 55 56@opindex std 57@opindex ansi 58@opindex pedantic 59@opindex pedantic-errors 60The original ANSI C standard (X3.159-1989) was ratified in 1989 and 61published in 1990. This standard was ratified as an ISO standard 62(ISO/IEC 9899:1990) later in 1990. There were no technical 63differences between these publications, although the sections of the 64ANSI standard were renumbered and became clauses in the ISO standard. 65This standard, in both its forms, is commonly known as @dfn{C89}, or 66occasionally as @dfn{C90}, from the dates of ratification. The ANSI 67standard, but not the ISO standard, also came with a Rationale 68document. To select this standard in GCC, use one of the options 69@option{-ansi}, @option{-std=c90} or @option{-std=iso9899:1990}; to obtain 70all the diagnostics required by the standard, you should also specify 71@option{-pedantic} (or @option{-pedantic-errors} if you want them to be 72errors rather than warnings). @xref{C Dialect Options,,Options 73Controlling C Dialect}. 74 75Errors in the 1990 ISO C standard were corrected in two Technical 76Corrigenda published in 1994 and 1996. GCC does not support the 77uncorrected version. 78 79An amendment to the 1990 standard was published in 1995. This 80amendment added digraphs and @code{__STDC_VERSION__} to the language, 81but otherwise concerned the library. This amendment is commonly known 82as @dfn{AMD1}; the amended standard is sometimes known as @dfn{C94} or 83@dfn{C95}. To select this standard in GCC, use the option 84@option{-std=iso9899:199409} (with, as for other standard versions, 85@option{-pedantic} to receive all required diagnostics). 86 87A new edition of the ISO C standard was published in 1999 as ISO/IEC 889899:1999, and is commonly known as @dfn{C99}. GCC has substantially 89complete support for this standard version; see 90@uref{http://gcc.gnu.org/c99status.html} for details. To select this 91standard, use @option{-std=c99} or @option{-std=iso9899:1999}. (While in 92development, drafts of this standard version were referred to as 93@dfn{C9X}.) 94 95Errors in the 1999 ISO C standard were corrected in three Technical 96Corrigenda published in 2001, 2004 and 2007. GCC does not support the 97uncorrected version. 98 99A fourth version of the C standard, known as @dfn{C11}, was published 100in 2011 as ISO/IEC 9899:2011. GCC has substantially complete support 101for this standard, enabled with @option{-std=c11} or 102@option{-std=iso9899:2011}. (While in development, drafts of this 103standard version were referred to as @dfn{C1X}.) 104 105By default, GCC provides some extensions to the C language that on 106rare occasions conflict with the C standard. @xref{C 107Extensions,,Extensions to the C Language Family}. Use of the 108@option{-std} options listed above will disable these extensions where 109they conflict with the C standard version selected. You may also 110select an extended version of the C language explicitly with 111@option{-std=gnu90} (for C90 with GNU extensions), @option{-std=gnu99} 112(for C99 with GNU extensions) or @option{-std=gnu11} (for C11 with GNU 113extensions). The default, if no C language dialect options are given, 114is @option{-std=gnu11}. Some features that are part of the C99 standard 115are accepted as extensions in C90 mode, and some features that are part 116of the C11 standard are accepted as extensions in C90 and C99 modes. 117 118The ISO C standard defines (in clause 4) two classes of conforming 119implementation. A @dfn{conforming hosted implementation} supports the 120whole standard including all the library facilities; a @dfn{conforming 121freestanding implementation} is only required to provide certain 122library facilities: those in @code{<float.h>}, @code{<limits.h>}, 123@code{<stdarg.h>}, and @code{<stddef.h>}; since AMD1, also those in 124@code{<iso646.h>}; since C99, also those in @code{<stdbool.h>} and 125@code{<stdint.h>}; and since C11, also those in @code{<stdalign.h>} 126and @code{<stdnoreturn.h>}. In addition, complex types, added in C99, are not 127required for freestanding implementations. The standard also defines 128two environments for programs, a @dfn{freestanding environment}, 129required of all implementations and which may not have library 130facilities beyond those required of freestanding implementations, 131where the handling of program startup and termination are 132implementation-defined, and a @dfn{hosted environment}, which is not 133required, in which all the library facilities are provided and startup 134is through a function @code{int main (void)} or @code{int main (int, 135char *[])}. An OS kernel would be a freestanding environment; a 136program using the facilities of an operating system would normally be 137in a hosted implementation. 138 139@opindex ffreestanding 140GCC aims towards being usable as a conforming freestanding 141implementation, or as the compiler for a conforming hosted 142implementation. By default, it will act as the compiler for a hosted 143implementation, defining @code{__STDC_HOSTED__} as @code{1} and 144presuming that when the names of ISO C functions are used, they have 145the semantics defined in the standard. To make it act as a conforming 146freestanding implementation for a freestanding environment, use the 147option @option{-ffreestanding}; it will then define 148@code{__STDC_HOSTED__} to @code{0} and not make assumptions about the 149meanings of function names from the standard library, with exceptions 150noted below. To build an OS kernel, you may well still need to make 151your own arrangements for linking and startup. 152@xref{C Dialect Options,,Options Controlling C Dialect}. 153 154GCC does not provide the library facilities required only of hosted 155implementations, nor yet all the facilities required by C99 of 156freestanding implementations on all platforms; to use the facilities of a hosted 157environment, you will need to find them elsewhere (for example, in the 158GNU C library). @xref{Standard Libraries,,Standard Libraries}. 159 160Most of the compiler support routines used by GCC are present in 161@file{libgcc}, but there are a few exceptions. GCC requires the 162freestanding environment provide @code{memcpy}, @code{memmove}, 163@code{memset} and @code{memcmp}. 164Finally, if @code{__builtin_trap} is used, and the target does 165not implement the @code{trap} pattern, then GCC will emit a call 166to @code{abort}. 167 168For references to Technical Corrigenda, Rationale documents and 169information concerning the history of C that is available online, see 170@uref{http://gcc.gnu.org/readings.html} 171 172@section C++ Language 173 174GCC supports the original ISO C++ standard (1998) and contains 175experimental support for the second ISO C++ standard (2011). 176 177The original ISO C++ standard was published as the ISO standard (ISO/IEC 17814882:1998) and amended by a Technical Corrigenda published in 2003 179(ISO/IEC 14882:2003). These standards are referred to as C++98 and 180C++03, respectively. GCC implements the majority of C++98 (@code{export} 181is a notable exception) and most of the changes in C++03. To select 182this standard in GCC, use one of the options @option{-ansi}, 183@option{-std=c++98}, or @option{-std=c++03}; to obtain all the diagnostics 184required by the standard, you should also specify @option{-pedantic} (or 185@option{-pedantic-errors} if you want them to be errors rather than 186warnings). 187 188A revised ISO C++ standard was published in 2011 as ISO/IEC 18914882:2011, and is referred to as C++11; before its publication it was 190commonly referred to as C++0x. C++11 contains several 191changes to the C++ language, most of which have been implemented in an 192experimental C++11 mode in GCC@. For information 193regarding the C++11 features available in the experimental C++11 mode, 194see @uref{http://gcc.gnu.org/projects/@/cxx0x.html}. To select this 195standard in GCC, use the option @option{-std=c++11}; to obtain all the 196diagnostics required by the standard, you should also specify 197@option{-pedantic} (or @option{-pedantic-errors} if you want them to 198be errors rather than warnings). 199 200More information about the C++ standards is available on the ISO C++ 201committee's web site at @uref{http://www.open-std.org/@/jtc1/@/sc22/@/wg21/}. 202 203By default, GCC provides some extensions to the C++ language; @xref{C++ 204Dialect Options,Options Controlling C++ Dialect}. Use of the 205@option{-std} option listed above will disable these extensions. You 206may also select an extended version of the C++ language explicitly with 207@option{-std=gnu++98} (for C++98 with GNU extensions) or 208@option{-std=gnu++11} (for C++11 with GNU extensions). The default, if 209no C++ language dialect options are given, is @option{-std=gnu++98}. 210 211@section Objective-C and Objective-C++ Languages 212@cindex Objective-C 213@cindex Objective-C++ 214 215GCC supports ``traditional'' Objective-C (also known as ``Objective-C 2161.0'') and contains support for the Objective-C exception and 217synchronization syntax. It has also support for a number of 218``Objective-C 2.0'' language extensions, including properties, fast 219enumeration (only for Objective-C), method attributes and the 220@@optional and @@required keywords in protocols. GCC supports 221Objective-C++ and features available in Objective-C are also available 222in Objective-C++@. 223 224GCC by default uses the GNU Objective-C runtime library, which is part 225of GCC and is not the same as the Apple/NeXT Objective-C runtime 226library used on Apple systems. There are a number of differences 227documented in this manual. The options @option{-fgnu-runtime} and 228@option{-fnext-runtime} allow you to switch between producing output 229that works with the GNU Objective-C runtime library and output that 230works with the Apple/NeXT Objective-C runtime library. 231 232There is no formal written standard for Objective-C or Objective-C++@. 233The authoritative manual on traditional Objective-C (1.0) is 234``Object-Oriented Programming and the Objective-C Language'', 235available at a number of web sites: 236@itemize 237@item 238@uref{http://www.gnustep.org/@/resources/@/documentation/@/ObjectivCBook.pdf} 239is the original NeXTstep document; 240@item 241@uref{http://objc.toodarkpark.net} 242is the same document in another format; 243@item 244@uref{http://developer.apple.com/@/mac/@/library/@/documentation/@/Cocoa/@/Conceptual/@/ObjectiveC/} 245has an updated version but make sure you search for ``Object Oriented Programming and the Objective-C Programming Language 1.0'', 246not documentation on the newer ``Objective-C 2.0'' language 247@end itemize 248 249The Objective-C exception and synchronization syntax (that is, the 250keywords @@try, @@throw, @@catch, @@finally and @@synchronized) is 251supported by GCC and is enabled with the option 252@option{-fobjc-exceptions}. The syntax is briefly documented in this 253manual and in the Objective-C 2.0 manuals from Apple. 254 255The Objective-C 2.0 language extensions and features are automatically 256enabled; they include properties (via the @@property, @@synthesize and 257@@dynamic keywords), fast enumeration (not available in 258Objective-C++), attributes for methods (such as deprecated, noreturn, 259sentinel, format), the unused attribute for method arguments, the 260@@package keyword for instance variables and the @@optional and 261@@required keywords in protocols. You can disable all these 262Objective-C 2.0 language extensions with the option 263@option{-fobjc-std=objc1}, which causes the compiler to recognize the 264same Objective-C language syntax recognized by GCC 4.0, and to produce 265an error if one of the new features is used. 266 267GCC has currently no support for non-fragile instance variables. 268 269The authoritative manual on Objective-C 2.0 is available from Apple: 270@itemize 271@item 272@uref{http://developer.apple.com/@/mac/@/library/@/documentation/@/Cocoa/@/Conceptual/@/ObjectiveC/} 273@end itemize 274 275For more information concerning the history of Objective-C that is 276available online, see @uref{http://gcc.gnu.org/readings.html} 277 278@section Go Language 279 280As of the GCC 4.7.1 release, GCC supports the Go 1 language standard, 281described at @uref{http://golang.org/doc/go1.html}. 282 283@section References for Other Languages 284 285@xref{Top, GNAT Reference Manual, About This Guide, gnat_rm, 286GNAT Reference Manual}, for information on standard 287conformance and compatibility of the Ada compiler. 288 289@xref{Standards,,Standards, gfortran, The GNU Fortran Compiler}, for details 290of standards supported by GNU Fortran. 291 292@xref{Compatibility,,Compatibility with the Java Platform, gcj, GNU gcj}, 293for details of compatibility between @command{gcj} and the Java Platform. 294