对静态类成员的未定义引用 [英] Undefined reference to static class member

问题描述

任何人都可以解释为什么下面的代码不会编译？至少在g ++ 4.2.4上。

Can anyone explain why following code won't compile? At least on g++ 4.2.4.

更有趣的是，为什么当我将MEMBER转换为int时会进行编译？

And more interesting, why it will compile when I cast MEMBER to int?

#include <vector>

class Foo {  
public:  
    static const int MEMBER = 1;  
};

int main(){  
    vector<int> v;  
    v.push_back( Foo::MEMBER );       // undefined reference to `Foo::MEMBER'
    v.push_back( (int) Foo::MEMBER ); // OK  
    return 0;
}

推荐答案

静态成员在某处（在类定义之后）。试试这个：

You need to actually define the static member somewhere (after the class definition). Try this:

class Foo { /* ... */ };

const int Foo::MEMBER;

int main() { /* ... */ }

这应该摆脱未定义的引用。

That should get rid of the undefined reference.

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