c++静态成员

c++静态成员-求助
C/C++ code
#include <iostream>
#include <string>
using namespace std;

class firstClass{
    public:
    static string first;
    string s;
    string st(){
        return s;
    }
    firstClass(){
        s="luoage@msn.cn";
    }
};

int main(){
    string firstClass::first="luoage@msn.cn";
    firstClass c;
    cout<<c.st();
    return 0;
}





编译错误如下:
class.cpp: In function 'int main()':
class.cpp:19:18: error: invalid use of qualified-name 'firstClass::first'

------解决方案--------------------
string firstClass::first="luoage@msn.cn";

放在main()函数之上