GCC编译器深度探索：选项详解与使用指南

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"GCC (GNU Compiler Collection) 是一个开源的、跨平台的编译器套件，由Richard M. Stallman和GCC开发者社区共同开发。它支持多种编程语言，如C、C++、Fortran、Java等，并且是GNU Project的重要组成部分。此资料可能详细介绍了GCC 4.5.4版本的特性、编译选项以及如何使用GCC进行程序编译。" GCC编译器是全球开发者广泛使用的工具，它的全称为GNU Compiler Collection，由GNU项目开发并维护。GCC不仅支持C语言，还支持C++、Objective-C、Fortran、Ada、Go等多种编程语言，为软件开发者提供了极大的便利。GCC 4.5.4是一个较旧但稳定的版本，包含了一系列优化和改进，适用于多种操作系统，包括Linux、Unix以及Windows等。在使用GCC时，理解编译选项是非常关键的。这些选项允许用户定制编译过程，例如控制优化级别（-O选项）、生成调试信息（-g选项）、指定目标架构或ABI（--target选项）、链接特定库（-l选项）等。优化级别从-O0到-O3，其中-O0表示不进行优化，而-O3则会进行最大程度的优化，可能会影响代码的可读性和调试性。-g选项用于在编译过程中包含调试信息，这对于使用GDB等调试工具至关重要。通过--target选项，开发者可以指定编译代码的目标平台，这在跨平台开发中很有用。此外，GCC还提供了预处理器、编译器、汇编器和链接器等一系列工具。预处理器（cpp）处理源代码中的宏定义和条件编译指令；编译器（gcc）将预处理后的源代码转换成汇编语言；汇编器（gas）将汇编代码转化为机器语言；最后，链接器（ld）负责将多个目标文件和库合并成一个可执行文件，解决符号引用的问题。 GCC的使用还包括配置、编译和安装步骤。在构建大型项目时，通常使用Makefile文件来自动化这些步骤。Makefile定义了规则和目标，使得编译过程更加有序和高效。通过`make`命令，开发者可以快速构建、测试和部署软件。在学习GCC的过程中，理解其错误和警告信息也非常重要，因为这些信息可以帮助开发者定位和修复代码中的问题。同时，GCC与其他GNU工具链如GDB、valgrind等配合使用，可以实现更强大的开发和调试功能。 GCC是一个强大且灵活的编译系统，它不仅提供了编译程序的基本功能，还支持高级优化、跨平台编译以及与其他开源工具的无缝集成。熟悉GCC的使用和配置，对于任何希望在开源世界中开发和贡献代码的人来说，都是必备的技能。

Chapter 2: Language Standards Supported by GCC 5

2 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.

2.1 C language

GCC supports three versions of the C standard, although support for the most recent version

is not yet complete.

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 te chnical 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 C89, or occasionally as 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 ‘-ansi’, ‘-std=c90’ or

‘-std=iso9899:1990’; to obtain all the diagnostics required by the standard, you should

also specify ‘-pedantic’ (or ‘-pedantic-errors’ if you want them to be errors rather than

warnings). See Section 3.4 [Options C ontrolling C Dialect], page 28.

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 __STDC_VERSION__ to the language, but otherwise concerned the library. This

amendment is commonly known as AMD1; the amended standard is sometimes known as

C94 or C95. To select this standard in GCC, use the option ‘-std=iso9899:199409’ (with,

as for other standard versions, ‘-pedantic’ to rec eive 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 C99. GCC has incomplete support for this standard version; see

http://gcc.gnu.org/gcc-4.5/c99status.html for details. To se lect this standard, use

‘-std=c99’ or ‘-std=iso9899:1999’. (While in development, drafts of this standard version

were referred to as 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.

By default, GCC provides some extensions to the C language that on rare o cc asions con-

ﬂict with the C standard. See Chapter 6 [Extensions to the C Language Family], page 277.

Use of the ‘-std’ options listed above will disable these extensions where they conﬂict with

the C standard version selected. You may also selec t an extended version of the C language

explicitly with ‘-std=gnu90’ (for C90 with GNU extensions) or ‘-std=gnu99’ (for C99 with

GNU extensions). The default, if no C language dialect options are given, is ‘-std=gnu90’;

this will change to ‘-std=gnu99’ in some future release when the C99 support is complete.

Some features that are part of the C99 standard are acc epted as extensions in C90 mode.

The ISO C standard deﬁnes (in clause 4) two classes of conforming implementation. A

conforming hosted implementation supports the whole standard including all the library fa-

cilities; a conforming freestanding implementation is only required to provide certain library

facilities: those in <float.h>, <limits.h>, <stdarg.h>, and <stddef.h>; since AMD1,

6 Using the GNU Compiler Collection (GCC)

also those in <iso646.h>; and in C99, also those in <stdbool.h> and <stdint.h>. In ad-

dition, complex types, added in C99, are not required for freestanding implementations. The

standard also deﬁnes two environments for programs, a 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 hosted environment, which is not required, in which all the

library facilities are provided and startup is through a function int main (void) or int

main (int, char *[]). An OS kernel would be a freestanding environment; a program

using the facilities of an operating sys tem would normally be in a hosted implementation.

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 __STDC_HOSTED__ as 1 and presuming that when the names

of ISO C functions are used, they have the se mantics deﬁned in the standard. To make it act

as a conforming freestanding implementation for a freestanding environment, use the option

‘-ffreestanding’; it will then deﬁne __STDC_HOSTED__ to 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. See Section 3.4 [Options Controlling C Dialect], page 28.

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). See Section 11.6 [Standard Libraries], page 596.

Most of the compiler support routines used by GCC are present in ‘libgcc’, but there

are a few exceptions. GCC requires the freestanding environment provide memcpy, memmove,

memset and memcmp. Finally, if __builtin_trap is use d, and the target does not implement

the trap pattern, then GCC will e mit a call to abort.

For references to Technical Corrigenda, Rationale documents and information concerning

the history of C that is available online, se e http://gcc.gnu.org/readings.html

2.2 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 m ajority

of C++98 (export is a notable e xception) and most of the changes in C++03. To select this

standard in GCC, use one of the options ‘-ansi’ or ‘-std=c++98’; to obtain all the diagnos-

tics required by the standard, you should also specify ‘-pedantic’ (or ‘-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++ commit-

tee’s web site at http://www.open-std.org/jtc1/sc22/wg21/. For information

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