explicit关键字

#include <iostream>

using namespace std;

class TestClass{

public:
    TestClass(){
        cout << "constructor" << endl;
    }
    TestClass(int a){
        cout << "constructor " << a << endl;
    }
};

class TestClass2{
public:
    TestClass2(){
        cout << "constructor" << endl;
    }
    explicit TestClass2(int a){
        cout << "constructor " << a << endl;
    }

};


int main(){
    TestClass t;
    TestClass t1 = 6;

    TestClass2 t2;
    TestClass2 t2 = 7;//编译通不过了~~~

    cout << "letben" << endl;
    system("pause");
}

参见：

http://baike.baidu.com/link?url=ZdpF1NVfUtlRZHDNbN3RWRjBDzkOSzMWojBJs7RAqVkzVKr8qCC62DhY2FoA7MqopOnG3L13Pi3eARBCLC_QLK