Subversion Repositories openrisc

@c Copyright (C) 2000, 2001, 2002, 2004, 2006, 2007, 2008, 2010

@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 C11

@cindex C11

@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/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{C11}, was published

in 2011 as ISO/IEC 9899:2011.  GCC has limited incomplete support for

parts of this standard, enabled with @option{-std=c11} or

@option{-std=iso9899:2011}.  (While in development, drafts of this

standard version were referred to as @dfn{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=gnu11} (for C11 with GNU

extensions).  The default, if no C language dialect

options are given, is @option{-std=gnu90}; this will change to

@option{-std=gnu99} or @option{-std=gnu11} in some future release when

the C99 or C11 support is

complete.  Some features that are part of the C99 standard are

accepted as extensions in C90 mode, and some features that are part of

the C11 standard are accepted as extensions in C90 and C99 modes.

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>}; since C99, also those in @code{<stdbool.h>} and

@code{<stdint.h>}; and since C11, also those in @code{<stdalign.h>}

and @code{<stdnoreturn.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 original ISO C++ standard (1998) and contains

experimental support for the second ISO C++ standard (2011).

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},

@option{-std=c++98}, or @option{-std=c++03}; 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).

A revised ISO C++ standard was published in 2011 as ISO/IEC

14882:2011, and is referred to as C++11; before its publication it was

commonly referred to as C++0x.  C++11 contains several

changes to the C++ language, most of which have been implemented in an

experimental C++11 mode in GCC@.  For information

regarding the C++11 features available in the experimental C++11 mode,

see @uref{http://gcc.gnu.org/projects/@/cxx0x.html}. To select this

standard in GCC, use the option @option{-std=c++11}; 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).

More information about the C++ standards is available on the ISO C++

committee's web site at @uref{http://www.open-std.org/@/jtc1/@/sc22/@/wg21/}.

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++11} (for C++11 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.