当存在与内联函数同名的extern函数时，将调用哪一个？
[英]Which one is called when existing an extern function with the same name as an inline function?
问题描述
test.cpp 
测试文件
#include <iostream>
void f()
{
std::cout<<"non-inline"<<std::endl;
}
main.cpp main.cpp
#include <iostream>
using namespace std;
inline void f()
{
cout<<"inline"<<endl;
}
int main()
{
f();
return 0;
}
In debug mode, the output is: non-inline. 在调试模式下，输出为：非内联。 command:g++ [-g] -o main main.cpp test.cpp 命令：g ++ [-g] -o main main.cpp test.cpp
In release mode, the output is: inline. 在发布模式下，输出为：内联。 command:g++ -O -o main main.cpp test.cpp 命令：g ++ -O -o main main.cpp test.cpp
Why? 为什么？
Linux G++ 4.7.3 Linux G ++ 4.7.3
In C99, an inline definition does not provide an external definition for the function, so we can provide an external definition of the identifier by defining another function in other source file. 在C99中，内联定义不为函数提供外部定义，因此我们可以通过在其他源文件中定义另一个函数来提供标识符的外部定义。
Does an inline definition provide an external definition for the function in C++?? 内联定义是否为C ++中的函数提供外部定义？
Thx！！ 谢谢！！
2 个解决方案
解决方案1
6 2013-09-05 06:39:51
Your program has UB (Undefined Behaviour), because it violates ODR (One Definition Rule) by providing two different definitions of f() . 您的程序具有UB（未定义行为），因为它通过提供f()两个不同定义来违反ODR（一个定义规则f() 。 There is therefore next to no way of reasoning why it behaves one way or the other. 因此，几乎没有理由推理它为什么以一种或另一种方式表现。 In the best tradition of UB, any behaviour is possible (including ordering pizza over the Internet). 按照UB的最佳传统，任何行为都是可能的（包括通过Internet订购披萨）。
EDIT 编辑
These quotes from the standard (ISO/IEC 14882:2011) prove it's UB: 这些来自标准（ISO / IEC 14882：2011）的引用证明它是UB：
[basic.def.odr]§3: [basic.def.odr]§3：
Every program shall contain exactly one definition of every non-inline function or variable that is odr-used in that program;
[basic.def.odr]§5: [basic.def.odr]§5：
There can be more than one definition of ... inline function with external linkage ... in a program provided that each definition appears in a different translation unit, and provided the definitions satisfy the following requirements.
- each definition of D shall consist of the same sequence of tokens;
- ...
[dcl.fct.spec]§4 [dcl.fct.spec]§4
An inline function shall be defined in every translation unit in which it is odr-used and shall have exactly the same definition in every case (3.2).
(Emphasis mine) （强调我的）
解决方案2
6 2013-09-05 06:42:29
Your program violate the One definition Rule then it is Undefined behavior . 您的程序违反了一个定义规则，那么它是未定义行为 。
When you have an Undefined behaviour , anything is possible but you have to know that the worst case will come during the most important demo ;) 当您有未定义的行为时 ，一切皆有可能，但您必须知道最重要的演示期间会出现最坏的情况；）
The standard says: 该标准说：
3.2 One definition rule [basic.def.odr]
1/ No translation unit shall contain more than one definition of any variable, function, class type, enumeration type, or template.
[...]
4/ Every program shall contain exactly one definition of every non-inline function or variable that is odr-used in that program;
5/ There can be more than one definition of [...] inline function with external linkage (7.1.2) [...] in a program provided that each definition appears in a different translation unit, and provided the definitions satisfy the following requirements.
each definition of D shall consist of the same sequence of tokens;
[...]
If the definitions of D satisfy all these requirements, then the program shall behave as if there were a single definition of D. If the definitions of D do not satisfy these requirements, then the behavior is undefined.
And later: 然后：
7.1.2 Function specifiers [dcl.fct.spec]
4/ An inline function shall be defined in every translation unit in which it is odr-used and shall have exactly the same definition in every case (3.2).
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