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Possible Duplicate:
What are copy elision and return value optimization?
我有以下程序:
#include <iostream>
using namespace std;
class Pointt {
public:
int x;
int y;
Pointt() {
x = 0;
y = 0;
cout << "def constructor called" << endl;
}
Pointt(int x, int y) {
this->x = x;
this->y = y;
cout << "constructor called" << endl;
}
Pointt(const Pointt& p) {
this->x = p.x;
this->y = p.y;
cout << "copy const called" << endl;
}
Pointt& operator=(const Pointt& p) {
this->x = p.x;
this->y = p.y;
cout << "op= called" << endl;
return *this;
}
};
Pointt func() {
cout << "func: 1" << endl;
Pointt p(1,2);
cout << "func: 2" << endl;
return p;
}
int main() {
cout << "main:1" << endl;
Pointt k = func();
cout << "main:2" << endl;
cout << k.x << " " << k.y << endl;
return 0;
}
我期望的输出如下:
main:1
func: 1
constructor called
func: 2
copy const called
op= called
main:2
1 2
但我得到以下信息:
main:1
func: 1
constructor called
func: 2
main:2
1 2
问题是:为什么不从 func 返回一个对象到 main 调用我的复制构造函数？