cpp11 return返回类对象的过程

code

#include <iostream>
 
using std::cout;
using std::endl;
 
class A {
public:
    A() {cout << "A()" << endl;}
    ~A() {cout << "~A()" << endl;}
    A(A& that) {cout << "A(A&)" << endl;}
    A& operator=(A& that) {cout << "operator=(A&)" << endl;}
    A(A&& that) {cout << "A(A&&)" << endl;}
    A& operator=(A&& taht) {cout << "operator=(A&&)" << endl;}
};
A demoA(void) {
    A a;
	cout << "------------" << endl;
    return a;
}
 
int main() {
	A a = demoA();
	return 0;
}

编译

g++ cpp11_return.cpp -std=c++11 -fno-elide-constructors

-fno-elide-constructors禁用nrvo优化

现象

解释

1.

demoA函数中构造a

2.

demoA函数返回时，用a 右值构造demoA函数的返回值

3.

demoA函数结束，析构a

4.

A a=demoA();语句，使用demoA的返回值 右值构造a

5.

A a=demoA()语句结束，析构demoA的返回值

6.

main函数结束，析构a