-D_XOPEN_SOURCE 是什么意思? [英] What does -D_XOPEN_SOURCE do/mean?

问题描述

我最近遇到了一些没有这个参数 gcc 将无法编译的代码.我检查了 gcc 手册页，但没有找到这个特定选项.我确实找到了 XOPEN_SOURCE，但几乎没有解释它的作用.

I recently encountered some code that gcc would not compile without this arg. I checked the gcc man page, but did not find this specific option. I did find XOPEN_SOURCE, but there was little explanation of what it does.

有人能详细说明一下吗?我知道 -D_XOPEN_SOURCE 可以设置为不同的值，例如 400、600，但它们有什么作用?

Can someone please elaborate? I know -D_XOPEN_SOURCE can be set to different values, such 400, 600, but what do those do?

推荐答案

什么时候做

#define _XOPEN_SOURCE <some number>

或

cc -D_XOPEN_SOURCE=<some number>

它告诉您的编译器包含一些在 X/Open 和 POSIX 标准中定义的额外函数的定义.

it tells your compiler to include definitions for some extra functions that are defined in the X/Open and POSIX standards.

这将为您提供一些在最新的 UNIX/BSD/Linux 系统上存在的额外功能，但在其他系统(如 Windows)上可能不存在.

This will give you some extra functionality that exists on most recent UNIX/BSD/Linux systems, but probably doesn't exist on other systems such as Windows.

数字代表标准的不同版本.

The numbers refer to different versions of the standard.

• 500 - X/Open 5，结合 POSIX 1995
• 600 - X/Open 6，结合 POSIX 2004
• 700 - X/Open 7，结合 POSIX 2008

您可以通过查看您调用的每个函数的手册页来判断您需要哪个函数(如果有).

You can tell which one you need (if any) by looking at the man page for each function you call.

例如，man strdup 说:

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       strdup(): _SVID_SOURCE || _BSD_SOURCE || _XOPEN_SOURCE >= 500
       strndup(), strdupa(), strndupa(): _GNU_SOURCE

这意味着您应该输入其中之一:

Which means that you should put one of these:

#define _SVID_SOURCE
#define _BSD_SOURCE
#define _XOPEN_SOURCE 500
#define _XOPEN_SOURCE 600
#define _XOPEN_SOURCE 700

如果您想使用 strdup，请在执行任何 #include 之前在源文件的顶部.

at the top of your source file before doing any #includes if you want to use strdup.

或者你可以把

#define _GNU_SOURCE

相反，它启用了所有功能，但缺点是它可能无法在 Solaris、FreeBSD、Mac OS X 等上编译.

there instead, which enables all functionality, with the downside that it might not compile on Solaris, FreeBSD, Mac OS X, etc.

在执行 #include、#define 或使用新函数之前检查每个手册页是个好主意，因为有时它们的行为会根据选项发生变化和 #define s，例如 basename(3).

It's a good idea to check each man page before doing a #include, #define, or using a new function, because sometimes their behavior changes depending on what options and #defines you have, for example with basename(3).

另见:

• Linux:gcc with -std=c99 抱怨不知道 struct timespec
• glibc 功能测试宏
• 编译环境 - 开放组基础规范问题 6(又名 X/Open 6))
• POSIX - 维基百科
• 单一 UNIX 规范 - 维基百科

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