c++ - C++ 中 const 的内部链接，但我得到重复的符号

Question

有人可以给点建议吗？

如果 C++ 中的 const 默认为内部链接，为什么我在下面的代码中会出现多个定义错误？

首先，文件dem.h:

#ifndef _DEM_H_
    #define _DEM_H_
    class Dem {
        public:
            static const int i;
    };

    const int Dem::i = 10;
#endif

它们imp1.cpp:

#include "dem.h"
#include <iostream>

using namespace std;
extern int foo();

int main() {
        cout << foo() << endl;
}

和imp2.cpp:

#include "dem.h"

int foo() {
    return Dem::i ;
}

我使用以下命令和结果进行编译:

$ g++ imp1.cpp imp2.cpp
/tmp/ccmGt0OY.o:imp2.cpp:(.rdata+0x0): multiple definition of `Dem::i'
/tmp/cc5sN7dz.o:imp1.cpp:(.rdata+0x0): first defined here
collect2: ld returned 1 exit status

Answer 1

来自 C++11 [basic.link]，第 5 段:

In addition, a member function, static data member, a named class or enumeration of class scope, or an unnamed class or enumeration defined in a class-scope typedef declaration such that the class or enumeration has the typedef name for linkage purposes (7.1.3), has external linkage if the name of the class has external linkage.

因为您的类有外部链接，所以您的静态数据成员也有。