一、重载运算符法
#include <stdio.h>
#include <iostream> class Three
{
int i;
public:
Three(int ii = , int = ) : i(ii)
{
std::cout << "you call Three()" << std::endl;
}
}; class Four
{
int x;
public:
Four(int xx) : x(xx) {}
operator Three() const { return Three(x);}
}; void g(Three) {}
int main()
{
Four four();
g(four);
g();//calls Three(1,0)
int n;
std::cin >> n;
}
//输出两次：
you call Three()
2.构造函数转换
//这个构造函数能够把另一类型的对象（引用）作为它的单个参数，那么构造函数允许编译器执行自动类型转换；
#include <stdio.h>
#include <iostream> class One
{
public:
One() {}
}; class Two
{
public:
Two(const One&)
{
std::cout << "you call Two()" << std::endl;
}
}; void f(Two) {} int main()
{
One one;
f(one);//wants a Two ,has a one
//输出："you call Two()”
int i;
std::cin >> i;
}
注意：以上方法调用了Two的隐藏的构造函数，如果关心调用效率的话不要这样使用！
3.阻止构造函数被隐式调用，要求必须显示调用:
//使用关键词explicit时，必须显示调用，完成类型转换
#include <stdio.h>
#include <iostream> using namespace std; class One
{
public:
One() { }
}; class Two
{
public:
explicit Two(const One&) {}
}; void f(Two) {} int main()
{
One one;
//!f(one);//NO auto conversion allowed
f(Two(one)); //int i;
//cin >> i;
}