C++类内定义静态变量

C++类内定义静态变量只限定与integral类型，比如int、char、long、float、double都行，但是string不行

#include<iostream>
#include<string>
using namespace std;

class testClass
{
public:
    static const int _dataI = 2;
    static const long _dataL = 389l;
    static const char _dataC = 'A';
};

class testClass2
{
public:
    static int _a;
};
int testClass2::_a = 89;

class testClass3
{
public:
    static const float _dataF = 2.3;
    static const double _dataD = 389;
//    static const string _dataS = "CourageK"; // not integral members
};

int main()
{
    cout<<testClass::_dataI<<endl;
    cout<<testClass::_dataL<<endl;
    cout<<testClass::_dataC<<endl;

    cout<<testClass2::_a<<endl;

    cout<<testClass3::_dataF<<endl;
    cout<<testClass3::_dataD<<endl;

    return 0;

}

输出结果为：

2

389

A

89

2.3

389