重载＆lt;＆lt;操作员ostream

Question

为什么以下行不起作用？

#include <iostream>

std::ostream& operator <<( std::ostream& os, const char *c)
{
    os << c; // why does this line doesn't work?
    return os;
}

int main()
{
    const char *c = "Hi";
    std::cout << c;
}

Answer 1

问题是std::ostream& operator <<( std::ostream& os, const char *c)已在iostream中重载。