重载操作符

C++语法规定可以重载操作符，例如*和->。下面是一个例子：

class Screen{
public:
    Screen(int x, int y)
    {
        m_x = x;
        m_y = y;
    }
    int m_x;
    int m_y;
};

template<class TYPE>
class ThreadLocal{
public:
    ThreadLocal(TYPE &s)
    {
        ptr = &s;
    }

    TYPE& operator*() {    return *ptr; }
    TYPE* operator->() { return ptr; }

private:
    TYPE *ptr;
};

int main(int argc, char* argv[])
{
    Screen s1(100, 60);
    ThreadLocal<Screen> ps(s1);
    printf("%d, %d\n%d, %d\n", (*ps).m_x, (*ps).m_y, ps->m_x, ps->m_y);

    return 0;
}

重载操作符很容易与转换函数混淆，例如下面的例子：

class Screen{
public:
    Screen(int x, int y)
    {
        m_x = x;
        m_y = y;
    }
    int m_x;
    int m_y;
};

template<class TYPE>
class ThreadLocal{
public:
    ThreadLocal(TYPE &s)
    {
        ptr = &s;
    }

    operator TYPE*() { return ptr; }
    TYPE* operator->() { return ptr; }

private:
    TYPE *ptr;
};

int main(int argc, char* argv[])
{
    Screen s1(100, 60);
    ThreadLocal<Screen> ps(s1);
    printf("%d, %d\n%d, %d\n", (*ps).m_x, (*ps).m_y, ps->m_x, ps->m_y);

    return 0;
}