一个定义规则-内联函数的多个定义 [英] One Definition Rule - Multiple definition of inline functions

问题描述

我正在阅读ODR，并且按规则说在整个程序中，对象或非内联函数不能具有多个定义 ，我尝试了以下操作...

I was reading ODR and as the rule says "In the entire program, an object or non-inline function cannot have more than one definition" and I tried the following...

file1.cpp

file1.cpp

#include <iostream>
using namespace std;

inline int func1(void){ return 5; }
inline int func2(void){ return 6; }
inline int func3(void){ return 7; }
int sum(void);

int main(int argc, char *argv[])
{
    cout << func1() << endl;
    cout << func2() << endl;
    cout << func3() << endl;
    cout << sum() << endl;
    return 0;
}

file2.cpp

file2.cpp

inline int func1(void) { return 5; }
inline int func2(void) { return 6; }
inline int func3(void) { return 7; }
int sum(void) { return func1() + func2() + func3(); }

它按规则说是有效的。我可以有多个内联函数定义。

It worked as the rule says. I can have multiple definition of inline functions.

• 非内联函数链接和内联函数链接有什么区别？


• 链接程序可区分这两个？

推荐答案

使函数 inline 做两件事（第二点与您的问题更相关）：

Making a function inline does two things (the second point is more relevant to your question):

1. 这是一个建议程序员对编译器的调用，可以通过内联扩展来快速调用此函数。粗略地说，内联扩展类似于将内联函数视为宏，通过其主体代码扩展对其的每次调用。这是一个建议-编译器可能不会（有时不能）执行各种优化。

1. It is a suggestion by the programmer to the compiler, to make calls to this function fast, possibly by doing inline expansion. Roughly, inline expansion is similar to treating the inline function like a macro, expanding each call to it, by the code of its body. This is a suggestion - the compiler may not (and sometimes cannot) perform various optimizations like that.

它指定了该功能是翻译单元的功能。因此，如果 inline 函数出现在 foo.cpp 中（要么是因为它被写在其中，要么是因为它是 #include 是在其中写入的标头，在这种情况下，预处理器基本上是这样做的）。现在，您编译 foo.cpp ，可能还编译其他的 bar.cpp ，其中也包含一个 inline 函数（可能是完全相同的签名；可能是由于 #include 使用相同的标头）。当链接器链接两个目标文件时，它不会被视为违反ODR，因为 inline 指令使文件的每个副本都位于其翻译单元的本地（通过编译有效创建的目标文件）。这不是建议，而是绑定。

It specifies the scope of the function to be that of a translation unit. So, if an inline function appears in foo.cpp (either because it was written in it, or because it #includes a header in which it was written, in which case the preprocessor basically makes it so). Now you compile foo.cpp, and possibly also some other bar.cpp which also contains an inline function with the same signature (possibly the exact same one; probably due to both #includeing the same header). When the linker links the two object files, it will not be considered a violation of the ODR, as the inline directive made each copy of the file local to its translation unit (the object file created by compiling it, effectively). This is not a suggestion, it is binding.

这些并非巧合两件事在一起。最常见的情况是 inline 函数出现在多个源文件的头文件 #include d中程序员希望请求快速的内联扩展。不过，这需要翻译单元的本地性规则，这样才不会出现链接器错误。

It is not coincidental that these two things go together. The most common case is for an inline function to appear in a header #included by several source files, probably because the programmer wanted to request fast inline expansion. This requires the translation-unit locality rule, though, so that linker errors shouldn't arise.

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