为什么不调用构造函数

[autohawk]

#include <iostream>
using namespace std;
class A
{
int i,j;
public:
A(){cout<<"A()"<<endl;}
A(int a,int b){i=a;j=b;cout<<"A(int,int)"<<endl;}
A(A & a)
{
i = a.i;
j = a.j;
cout<<"A(A&a)"<<i<<""<<j<<endl;
}
friend A operator + (A a,A b);
};

A operator+ (A a,A b)
{
return A(a.i+ b.i,a.j+b.j);
}

int main()

{
return 0;
}

编译报错，error: no matching function for call to 'A::A(A)'
操作符重载时为什么不自动调用A的构造函数？

[xhs_lh04]

A operator+ (A &a,A &b)

[太乙]

//lz用的是vc6.0吧？？这是微软的一个欠佳的地方！！头文件换换就行了
#include <iostream.h> 
//using namespace std; 
class A 
{ 
    int i,j; 
public: 
    A(){cout <<"A()" <<endl;} 
    A(int a,int b){i=a;j=b;cout <<"A(int,int)" <<endl;} 
    A(A & a) 
    { 
        i = a.i; 
        j = a.j; 
        cout <<"A(A&a)" <<i <<"" <<j <<endl; 
    } 
    friend A operator+(const A& a,const A& b); 
}; 

A operator+(const A& a,const A& b) 
{ 
    return A(a.i+ b.i,a.j+b.j); 
} 

int main() 

{ 
	return 0; 
} 

[nickshen_qidian]

2楼正解！

[我看你有戏]

#include <iostream> 
using namespace std; 
class A 
{ 
    int i,j; 
public: 
    A(){cout <<"A()" <<endl;} 
    A(int a,int b){i=a;j=b;cout <<"A(int,int)" <<endl;} 
    A(A & a) 
    { 
        i = a.i; 
        j = a.j; 
        cout <<"A(A&a)" <<i <<"" <<j <<endl; 
    } 
    friend A operator + (A a,A b); 
}; 

A operator+ (A a,A b) 
{ 
    return A(a.i+ b.i,a.j+b.j); 
} 

int main() 

{ 
	return 0; 
} 

[autohawk]

大哥们，要动手测试，我用的是gcc，当然我代码有问题。
这样吧，改为如下：
#include <iostream>
using namespace std;
class A
{
int i,j;
public:
A(){cout<<"A()"<<endl;}
A(int a,int b){i=a;j=b;cout<<"A(int,int)"<<endl;}
A(A & a)
{
i = a.i;
j = a.j;
cout<<"A(A&a)"<<i<<""<<j<<endl;
}
};
friend A operator + (A& a,A& b);
A operator+ (A& a,A& b)
{
/*
A temp(1,1);
return temp;//这样正常
*/
return A(1,1);//这样不行，why？
}

int main()

{
A(1,1);
return 0;
}

[autohawk]

明白明白了，我自己的问题，MMD，文件保存为.C的了