友元函数的实现位置

try the following source code. I added only minimal comments. Good luck!


[CODE]#include <iostream>

using namespace std;
// This is a delcaration, but not a definition.
class A; // forward declaration (1)
class B
{
public:
void F();
void F2(A& a); // (1) is necessary since we need to know type A here
};

void B::F() // this needs type B to be defined
{
cout<<"B::F() called.\n";
}

class A
{
friend void B::F();
friend void B::F2(A& a);
private:
int i;
};
void B::F2(A& a) // this nees type both type B and A to be defined
{
a.i = 100;
cout<<"B::F2() called.\n";
}
int main(int argc, char** argv)
{
A objA;
B objB;
objB.F();
objB.F2(objA);
return 0;
}[/CODE]