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diff --git a/gcc/doc/standards.texi b/gcc/doc/standards.texi new file mode 100644 index 000000000..d9a93db90 --- /dev/null +++ b/gcc/doc/standards.texi @@ -0,0 +1,294 @@ +@c Copyright (C) 2000, 2001, 2002, 2004, 2006, 2007, 2008, 2010, 2011 +@c Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Standards +@chapter Language Standards Supported by GCC + +For each language compiled by GCC for which there is a standard, GCC +attempts to follow one or more versions of that standard, possibly +with some exceptions, and possibly with some extensions. + +@section C language +@cindex C standard +@cindex C standards +@cindex ANSI C standard +@cindex ANSI C +@cindex ANSI C89 +@cindex C89 +@cindex ANSI X3.159-1989 +@cindex X3.159-1989 +@cindex ISO C standard +@cindex ISO C +@cindex ISO C90 +@cindex ISO/IEC 9899 +@cindex ISO 9899 +@cindex C90 +@cindex ISO C94 +@cindex C94 +@cindex ISO C95 +@cindex C95 +@cindex ISO C99 +@cindex C99 +@cindex ISO C9X +@cindex C9X +@cindex ISO C1X +@cindex C1X +@cindex Technical Corrigenda +@cindex TC1 +@cindex Technical Corrigendum 1 +@cindex TC2 +@cindex Technical Corrigendum 2 +@cindex TC3 +@cindex Technical Corrigendum 3 +@cindex AMD1 +@cindex freestanding implementation +@cindex freestanding environment +@cindex hosted implementation +@cindex hosted environment +@findex __STDC_HOSTED__ + +GCC supports three versions of the C standard, although support for +the most recent version is not yet complete. + +@opindex std +@opindex ansi +@opindex pedantic +@opindex pedantic-errors +The original ANSI C standard (X3.159-1989) was ratified in 1989 and +published in 1990. This standard was ratified as an ISO standard +(ISO/IEC 9899:1990) later in 1990. There were no technical +differences between these publications, although the sections of the +ANSI standard were renumbered and became clauses in the ISO standard. +This standard, in both its forms, is commonly known as @dfn{C89}, or +occasionally as @dfn{C90}, from the dates of ratification. The ANSI +standard, but not the ISO standard, also came with a Rationale +document. To select this standard in GCC, use one of the options +@option{-ansi}, @option{-std=c90} or @option{-std=iso9899:1990}; to obtain +all the diagnostics required by the standard, you should also specify +@option{-pedantic} (or @option{-pedantic-errors} if you want them to be +errors rather than warnings). @xref{C Dialect Options,,Options +Controlling C Dialect}. + +Errors in the 1990 ISO C standard were corrected in two Technical +Corrigenda published in 1994 and 1996. GCC does not support the +uncorrected version. + +An amendment to the 1990 standard was published in 1995. This +amendment added digraphs and @code{__STDC_VERSION__} to the language, +but otherwise concerned the library. This amendment is commonly known +as @dfn{AMD1}; the amended standard is sometimes known as @dfn{C94} or +@dfn{C95}. To select this standard in GCC, use the option +@option{-std=iso9899:199409} (with, as for other standard versions, +@option{-pedantic} to receive all required diagnostics). + +A new edition of the ISO C standard was published in 1999 as ISO/IEC +9899:1999, and is commonly known as @dfn{C99}. GCC has incomplete +support for this standard version; see +@uref{http://gcc.gnu.org/gcc-4.6/c99status.html} for details. To select this +standard, use @option{-std=c99} or @option{-std=iso9899:1999}. (While in +development, drafts of this standard version were referred to as +@dfn{C9X}.) + +Errors in the 1999 ISO C standard were corrected in three Technical +Corrigenda published in 2001, 2004 and 2007. GCC does not support the +uncorrected version. + +A fourth version of the C standard, known as @dfn{C1X}, is under +development; GCC has limited preliminary support for parts of this +standard, enabled with @option{-std=c1x}. + +By default, GCC provides some extensions to the C language that on +rare occasions conflict with the C standard. @xref{C +Extensions,,Extensions to the C Language Family}. Use of the +@option{-std} options listed above will disable these extensions where +they conflict with the C standard version selected. You may also +select an extended version of the C language explicitly with +@option{-std=gnu90} (for C90 with GNU extensions), @option{-std=gnu99} +(for C99 with GNU extensions) or @option{-std=gnu1x} (for C1X with GNU +extensions). The default, if no C language dialect +options are given, is @option{-std=gnu90}; this will change to +@option{-std=gnu99} in some future release when the C99 support is +complete. Some features that are part of the C99 standard are +accepted as extensions in C90 mode. + +The ISO C standard defines (in clause 4) two classes of conforming +implementation. A @dfn{conforming hosted implementation} supports the +whole standard including all the library facilities; a @dfn{conforming +freestanding implementation} is only required to provide certain +library facilities: those in @code{<float.h>}, @code{<limits.h>}, +@code{<stdarg.h>}, and @code{<stddef.h>}; since AMD1, also those in +@code{<iso646.h>}; and in C99, also those in @code{<stdbool.h>} and +@code{<stdint.h>}. In addition, complex types, added in C99, are not +required for freestanding implementations. The standard also defines +two environments for programs, a @dfn{freestanding environment}, +required of all implementations and which may not have library +facilities beyond those required of freestanding implementations, +where the handling of program startup and termination are +implementation-defined, and a @dfn{hosted environment}, which is not +required, in which all the library facilities are provided and startup +is through a function @code{int main (void)} or @code{int main (int, +char *[])}. An OS kernel would be a freestanding environment; a +program using the facilities of an operating system would normally be +in a hosted implementation. + +@opindex ffreestanding +GCC aims towards being usable as a conforming freestanding +implementation, or as the compiler for a conforming hosted +implementation. By default, it will act as the compiler for a hosted +implementation, defining @code{__STDC_HOSTED__} as @code{1} and +presuming that when the names of ISO C functions are used, they have +the semantics defined in the standard. To make it act as a conforming +freestanding implementation for a freestanding environment, use the +option @option{-ffreestanding}; it will then define +@code{__STDC_HOSTED__} to @code{0} and not make assumptions about the +meanings of function names from the standard library, with exceptions +noted below. To build an OS kernel, you may well still need to make +your own arrangements for linking and startup. +@xref{C Dialect Options,,Options Controlling C Dialect}. + +GCC does not provide the library facilities required only of hosted +implementations, nor yet all the facilities required by C99 of +freestanding implementations; to use the facilities of a hosted +environment, you will need to find them elsewhere (for example, in the +GNU C library). @xref{Standard Libraries,,Standard Libraries}. + +Most of the compiler support routines used by GCC are present in +@file{libgcc}, but there are a few exceptions. GCC requires the +freestanding environment provide @code{memcpy}, @code{memmove}, +@code{memset} and @code{memcmp}. +Finally, if @code{__builtin_trap} is used, and the target does +not implement the @code{trap} pattern, then GCC will emit a call +to @code{abort}. + +For references to Technical Corrigenda, Rationale documents and +information concerning the history of C that is available online, see +@uref{http://gcc.gnu.org/readings.html} + +@section C++ language + +GCC supports the ISO C++ standard (1998) and contains experimental +support for the upcoming ISO C++ standard (200x). + +The original ISO C++ standard was published as the ISO standard (ISO/IEC +14882:1998) and amended by a Technical Corrigenda published in 2003 +(ISO/IEC 14882:2003). These standards are referred to as C++98 and +C++03, respectively. GCC implements the majority of C++98 (@code{export} +is a notable exception) and most of the changes in C++03. To select +this standard in GCC, use one of the options @option{-ansi} or +@option{-std=c++98}; to obtain all the diagnostics required by the +standard, you should also specify @option{-pedantic} (or +@option{-pedantic-errors} if you want them to be errors rather than +warnings). + +The ISO C++ committee is working on a new ISO C++ standard, dubbed +C++0x, that is intended to be published by 2009. C++0x contains several +changes to the C++ language, some of which have been implemented in an +experimental C++0x mode in GCC@. The C++0x mode in GCC tracks the draft +working paper for the C++0x standard; the latest working paper is +available on the ISO C++ committee's web site at +@uref{http://www.open-std.org/@/jtc1/@/sc22/@/wg21/}. For information +regarding the C++0x features available in the experimental C++0x mode, +see @uref{http://gcc.gnu.org/projects/@/cxx0x.html}. To select this +standard in GCC, use the option @option{-std=c++0x}; to obtain all the +diagnostics required by the standard, you should also specify +@option{-pedantic} (or @option{-pedantic-errors} if you want them to be +errors rather than warnings). + +By default, GCC provides some extensions to the C++ language; @xref{C++ +Dialect Options,Options Controlling C++ Dialect}. Use of the +@option{-std} option listed above will disable these extensions. You +may also select an extended version of the C++ language explicitly with +@option{-std=gnu++98} (for C++98 with GNU extensions) or +@option{-std=gnu++0x} (for C++0x with GNU extensions). The default, if +no C++ language dialect options are given, is @option{-std=gnu++98}. + +@section Objective-C and Objective-C++ languages +@cindex Objective-C +@cindex Objective-C++ + +GCC supports ``traditional'' Objective-C (also known as ``Objective-C +1.0'') and contains support for the Objective-C exception and +synchronization syntax. It has also support for a number of +``Objective-C 2.0'' language extensions, including properties, fast +enumeration (only for Objective-C), method attributes and the +@@optional and @@required keywords in protocols. GCC supports +Objective-C++ and features available in Objective-C are also available +in Objective-C++@. + +GCC by default uses the GNU Objective-C runtime library, which is part +of GCC and is not the same as the Apple/NeXT Objective-C runtime +library used on Apple systems. There are a number of differences +documented in this manual. The options @option{-fgnu-runtime} and +@option{-fnext-runtime} allow you to switch between producing output +that works with the GNU Objective-C runtime library and output that +works with the Apple/NeXT Objective-C runtime library. + +There is no formal written standard for Objective-C or Objective-C++@. +The authoritative manual on traditional Objective-C (1.0) is +``Object-Oriented Programming and the Objective-C Language'', +available at a number of web sites: +@itemize +@item +@uref{http://www.gnustep.org/@/resources/@/documentation/@/ObjectivCBook.pdf} +is the original NeXTstep document; +@item +@uref{http://objc.toodarkpark.net} +is the same document in another format; +@item +@uref{http://developer.apple.com/@/mac/@/library/@/documentation/@/Cocoa/@/Conceptual/@/ObjectiveC/} +has an updated version but make sure you search for ``Object Oriented Programming and the Objective-C Programming Language 1.0'', +not documentation on the newer ``Objective-C 2.0'' language +@end itemize + +The Objective-C exception and synchronization syntax (that is, the +keywords @@try, @@throw, @@catch, @@finally and @@synchronized) is +supported by GCC and is enabled with the option +@option{-fobjc-exceptions}. The syntax is briefly documented in this +manual and in the Objective-C 2.0 manuals from Apple. + +The Objective-C 2.0 language extensions and features are automatically +enabled; they include properties (via the @@property, @@synthesize and +@@dynamic keywords), fast enumeration (not available in +Objective-C++), attributes for methods (such as deprecated, noreturn, +sentinel, format), the unused attribute for method arguments, the +@@package keyword for instance variables and the @@optional and +@@required keywords in protocols. You can disable all these +Objective-C 2.0 language extensions with the option +@option{-fobjc-std=objc1}, which causes the compiler to recognize the +same Objective-C language syntax recognized by GCC 4.0, and to produce +an error if one of the new features is used. + +GCC has currently no support for non-fragile instance variables. + +The authoritative manual on Objective-C 2.0 is available from Apple: +@itemize +@item +@uref{http://developer.apple.com/@/mac/@/library/@/documentation/@/Cocoa/@/Conceptual/@/ObjectiveC/} +@end itemize + +For more information concerning the history of Objective-C that is +available online, see @uref{http://gcc.gnu.org/readings.html} + +@section Go language + +The Go language continues to evolve as of this writing; see the +@uref{http://golang.org/@/doc/@/go_spec.html, current language +specifications}. At present there are no specific versions of Go, and +there is no way to describe the language supported by GCC in terms of +a specific version. In general GCC tracks the evolving specification +closely, and any given release will support the language as of the +date that the release was frozen. + +@section References for other languages + +@xref{Top, GNAT Reference Manual, About This Guide, gnat_rm, +GNAT Reference Manual}, for information on standard +conformance and compatibility of the Ada compiler. + +@xref{Standards,,Standards, gfortran, The GNU Fortran Compiler}, for details +of standards supported by GNU Fortran. + +@xref{Compatibility,,Compatibility with the Java Platform, gcj, GNU gcj}, +for details of compatibility between @command{gcj} and the Java Platform. |