为什么显式调用operator <<不明确？

Question

Here is the simple code :

int main()
{
    int x=0;
    std::cout<<x; 
    operator<<(std::cout,x); //ambiguous

    return 0;
}

Why is the operator<<(std::cout,x) call ambiguous but not std::cout<<x; ? Thanks

Answer 1

The problem here is that for outputting integers, operator<< is an std::ostream member function .

So to explicitly call the operator function you should do eg

std::cout.operator<<(x);

The stand-alone operator<< function is for characters and strings.