C固定inline函数重新定义规则 [英] C static inline function redefinition rules

问题描述

假设在 bar.h 有可能的存在：

static inline int fun () { return 2; }

和确保乐趣始终定义 foo.h中包含以下内容：

And to ensure that fun is always defined foo.h contains the following:

static inline int fun () { return 3; }

执行以下操作引起未定义行为时 bar.h 包含定义？

#include "foo.h" /* ensure there is always a definition */
#include "bar.h" /* use the bar definition if it exists */

int main () {
   /* ... */
   int x = fun ();
   /* ... */

与海湾合作委员会（4.0.1）（旧，但它是我目前拥有）的行为是按预期 - 酒吧版本丢失时foo的版本，使用时存在使用栏版本。

With gcc (4.0.1) (old, but it's what I have currently) the behavior is as expected - the foo version is used when the bar version is missing and the bar version is used when it exists.

推荐答案

没有，这是不允许的。的有趣的定义（）声明乐趣（）来有内部链接（由于静态），并在§6.9C标准说：

No, this is not allowed. Those definitions of fun() declare fun() to have internal linkage (due to the static), and §6.9 in the C standard says:

有不得超过一个
  对于每个外部定义
  标识符与内部声明
  联动在翻译单元。

There shall be no more than one external definition for each identifier declared with internal linkage in a translation unit.

一个应子句不确定的行为，这意味着你的程序的语义是完全不确定的，并且编译器没有发出错误消息的冲突。

Violation of a "shall" clause is undefined behaviour, which means that the semantics of your program are completely undefined, and the compiler doesn't have to issue an error message.

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