Question

这是我的源代码：

#include <iostream>
#include <memory>
#include <vector>

using namespace std;

class Copy {
public:

    Copy() {
        cout << "Constructor called" << endl;
    };

    Copy(const Copy& copy) {
        cout << "Copy constructor called" << endl;
    }

    Copy& operator=(Copy copy) {
        cout << "Copy-Assign constructor called" << endl;
        return *this;
    }

    Copy(Copy &&copy) noexcept {
        cout << "Move constructor called" << endl;
    }

    Copy& operator=(Copy &&copy) noexcept {
        cout << "Move-Assign constructor called" << endl;
        return *this;
    }

    ~Copy() {
        cout << "Destructor called" << endl;
    }
};

Copy TestCopy() {
    Copy cop;
    return cop;
}

vector<Copy> TestCopyVector() {
    vector<Copy> copyVector = vector<Copy>{Copy()};
    return copyVector;
}

int main()
{
    Copy cop = TestCopy();
    //TestCopy();
    //vector<Copy> copyVector = TestCopyVector();

    return 0;
}

在我的理解中

Copy cop = TestCopy();

应该调用Copy的移动分配。虽然输出如下：

$ ./test 
Constructor called
Destructor called

你能帮忙解释一下吗？感谢。

Answer 1

它被称为RVO (Return value optimization)，它是一个众所周知的优化，编译器可以在类似情况下进行优化。

为什么构造函数/析构函数被调用一次？

1 个答案: