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#pragma是什么?

aquatic 2002-05-07 04:16:18
#pragma是什么?
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shawn_liu 2002-05-07
具体的MSDN上有,不看E文,可不是好习惯,毕竟,不是所有资料都有中文译本的。
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shawn_liu 2002-05-07
抱歉,实在没空翻译英文资料。
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aquatic 2002-05-07
一般的实现是怎样的?能说说?
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shawn_liu 2002-05-07
简单的说,#pragma是一条预编译指令,利用这条指令可以获得一些硬件或操作系统专一的功能,同时又兼顾了兼容性。即在不影响兼容性的前提下,提供一些条件编译。比如说,在98及2000下,有些功能不同,我编的程序,即要在98和2000地环境中都能运行,还要在2000的环境下,利用它的新特性,就可以利用这条指令。
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aquatic 2002-05-07
msdn的E文我看不懂!
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shawn_liu 2002-05-07
Pragma Directives
Each implementation of C and C++ supports some features unique to its host machine or operating system. Some programs, for instance, need to exercise precise control over the memory areas where data is placed or to control the way certain functions receive parameters. The #pragma directives offer a way for each compiler to offer machine- and operating-system-specific features while retaining overall compatibility with the C and C++ languages. Pragmas are machine- or operating-system-specific by definition, and are usually different for every compiler.

Syntax

#pragma token-string

The token-string is a series of characters that gives a specific compiler instruction and arguments, if any. The number sign (#) must be the first non-white-space character on the line containing the pragma; white-space characters can separate the number sign and the word pragma. Following #pragma, write any text that the translator can parse as preprocessing tokens. The argument to #pragma is subject to macro expansion.

If the compiler finds a pragma it does not recognize, it issues a warning, but compilation continues.

Pragmas can be used in conditional statements, to provide new preprocessor functionality, or to provide implementation-defined information to the compiler. The C and C++ compilers recognize the following pragmas:

alloc_text comment init_seg1 optimize
auto_inline component inline_depth pack
bss_seg data_seg inline_recursion pointers_to_members1
check_stack function intrinsic setlocale
code_seg hdrstop message vtordisp1
const_seg include_alias once warning
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