错误：使用未声明的标识符“errno_t”的 [英] error: use of undeclared identifier 'errno_t'

问题描述

下面是我死了简单的虚拟code：

Here is my dead simple dummy code:

#include <errno.h>

int main(void)
{
    errno_t e;
    return 0;
}

这令人惊讶引发此错误：

Which surprisingly raises this error:

main.c:5:5: error: use of undeclared identifier 'errno_t'
    errno_t x;
    ^

我开始的遵循痕迹的：当编译器看到＆LT; ...＆GT; 夹杂它会先看看 / usr / include目录其中，当然，我发现 errno.h中文件。其实它在一个单一的线，除了许可证评论，这是：

I started to follow the traces: when the compiler sees the <...> inclusions it will first look at /usr/include where of course I found errno.h file. Actually it has a single line in it, besides the license comment, which is:

#include <sys/errno.h>

现在，在 / usr / include目录中的 errno.h中 / SYS 我发现下面几行：

Now, at /usr/include/sys in errno.h I found the following lines:

#include <sys/cdefs.h>

#if defined(__STDC_WANT_LIB_EXT1__) && __STDC_WANT_LIB_EXT1__ >= 1
#include <sys/_types/_errno_t.h>
#endif

而在 / usr / include目录/ _types 在 _errno_t.h 我发现这一点：

typedef int errno_t;

因此​​，看起来，它的存在，它是整数类型的别名，的 errno.h中部分 - 就像它应该是。

So it looks like, it is there, and it is an alias of the integer type, and part of the errno.h -- just as it should be.

那么，为什么是不是包括在内？为什么编译器引发未声明的标识符错误？

Then why isn't it included? Why the compiler raises the undeclared identifier error?

在此先感谢！

相关信息：的

RELEVANT INFO:

Compiler:
    Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)`

Compiler flags:
    -std=c11 -I/usr/include/sys -I/usr/local/include

---

宏变量 __ STDC_WANT_LIB_EXT1 __ 将在定义 / usr / include目录中的 / SYS cdefs.h在以下行：

---

The macro variable __STDC_WANT_LIB_EXT1__ will be defined at /usr/include/sys in cdefs.h in the following lines:

/* If the developer has neither requested a strict language mode nor a version
 * of POSIX, turn on functionality provided by __STDC_WANT_LIB_EXT1__ as part
 * of __DARWIN_C_FULL.
 */
#if !defined(__STDC_WANT_LIB_EXT1__) && !defined(__STRICT_ANSI__) && __DARWIN_C_LEVEL >= __DARWIN_C_FULL
#define __STDC_WANT_LIB_EXT1__ 1
#endif

---

更新：的

---

UPDATE:

由于@PaulR在评论区说：如果我删除 -std = C11 标志，它编译。这是一样令人惊讶，如果被列入该标志作为引发的错误。所以我用一个子问题，延长了这个问题：

As @PaulR said in the comment section: if I remove the -std=c11 flag, it compiles. Which is just as surprising as the error raised if the flag was included. So I extend this question with a sub-question:

的不 errno_t 的C11标准的一部分，或者为什么没有收录，当编译器规定的标准？的

Is not errno_t part of the C11 standard, or why isn't it included, when the standard is specified for the compiler?

推荐答案

errno_t 不是一个标准的类型;它是可选的（和广泛不喜欢和不支持的）附件K，包括ISO C11只与忽视，破坏标准的历史，因为一个特定的供应商的一部分。

errno_t is not a standard type; it's part of the optional (and widely disliked and unsupported) Annex K, included with ISO C11 only because of one particular vendor with a history of ignoring and sabotaging the standard.

由于附件K定义 errno_t 为 INT 的错误号对象 INT ，和所有的错误codeS是 INT ，只需使用<$ C在程序$ C> INT 。它不是依靠一个可选功能，它是不太可能支持更便携。

Since Annex K defines errno_t as int, the type of the errno object is int, and all error codes are int, simply use int in your programs. It's much more portable than relying on an optional feature which is unlikely to be supported.

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