GCC编译器详解：使用指南与参数解析

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"GCC编译手册是关于GNU Compiler Collection (GCC) 的详细指南，专注于解释编译参数的使用。这份手册适用于GCC版本4.7.2，由Richard M. Stallman和GCC开发者社区编写，由GNUPress出版。手册提供了解析GCC编译过程、优化选项以及针对不同编程语言（如C、C++、Fortran等）的特定编译设置等全面信息。" GCC，全称GNU Compiler Collection，是一个开源的、跨平台的编译器套件，支持多种编程语言，包括C、C++、Objective-C、Fortran、Ada以及Go等。手册的内容通常会涵盖以下几个关键知识点： 1. **基本使用**：介绍如何运行GCC，包括基本的编译命令行选项，如`-c`用于编译源代码到目标文件，`-o`指定输出文件名，以及`-Wall`开启所有警告。 2. **编译阶段**：GCC编译过程分为预处理、编译、汇编和链接四个阶段。手册会详细解释每个阶段的作用和可选参数，帮助用户理解代码是如何从源文件转化为可执行程序的。 3. **优化选项**：GCC提供了多级优化选项，如 `-O1`、`-O2` 和 `-O3`，分别对应不同级别的优化程度。手册会详细解释这些选项对代码性能的影响。 4. **调试支持**：GCC支持生成调试信息，如`-g`选项，使得GDB等调试工具可以正确地与编译后的代码配合使用。 5. **多文件项目**：对于包含多个源文件的项目，手册会介绍如何组织编译过程，包括使用`make`工具和链接选项。 6. **语言特定特性**：GCC对每种支持的语言都有特定的编译选项和注意事项，手册会列出这些特性，例如C++的名称空间管理或Fortran的模块处理。 7. **代码兼容性**：GCC手册也会涉及向后兼容性和标准合规性，比如如何编译符合C99、C++11等标准的代码。 8. **错误和警告**：GCC在编译过程中产生的错误和警告信息有详细的解释，有助于开发者诊断和修复问题。 9. **嵌入式系统**：对于嵌入式开发，GCC提供了交叉编译的支持，手册会指导如何配置和使用交叉编译环境。 10. **库和头文件**：如何链接外部库，以及处理头文件的包含路径，也是手册的重要部分。最后，GCC编译手册遵循GNU Free Documentation License，允许自由复制、分发和修改，以促进知识的共享和传播。因此，读者不仅可以学习到GCC的使用，还可以根据自己的需求对手册进行个性化定制。

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 technical diﬀerences between these publications, although the s ec tions 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 29.

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-4.7/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.

A fourth version of the C standard, known as C11, was published in 2011 as ISO/IEC

9899:2011. GCC has limited incomplete support for parts of this standard, enabled with

‘-std=c11’ or ‘-std=iso9899:2011’. (While in development, drafts of this standard version

were referred to as C1X.)

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

ﬂict with the C standard. See Chapter 6 [Extensions to the C Language Family], page 309.

Use of the ‘-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 lan-

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

with GNU extensions) or ‘-std=gnu11’ (for C11 with GNU extensions). The default, if

no C language dialect options are given, is ‘-std=gnu90’; this will change to ‘-std=gnu99’

or ‘-std=gnu11’ in some future release when the C99 or C11 support is complete. Some

6 Using the GNU Compiler Collection (GCC)

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

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,

also those in <iso646.h>; since C99, also those in <stdbool.h> and <stdint.h>; and since

C11, also those in <stdalign.h> and <stdnoreturn.h>. In addition, complex types, added

in C99, are not required for freestanding implementations. The standard also deﬁnes two

environments for programs, a frees tanding 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

system 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 semantics 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 29.

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 668.

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 used, and the target do es 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 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, res pe ctively. GCC implements the m ajority

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

this standard in GCC, use one of the options ‘-ansi’, ‘-std=c++98’, or ‘-std=c++03’; to

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