C ++是否优化了构建和复制到复制构造函数中？(Does C++ optimise construction

C ++是否优化了构建和复制到复制构造函数中？(Does C++ optimise construction-and-copy into a copy constructor?)

C ++编译器是否自动转换：

MyObject object2 = object1;

成

MyObject object2( object1 );

？

还是它对待它：

MyObject object2; object2 = object1;

？

Does a C++ compiler automatically convert:

MyObject object2 = object1;

into

MyObject object2( object1 );

?

Or does it treat it like:

MyObject object2; object2 = object1;

?

最满意答案

你可以试试看看确切的行为：

#include <iostream> class MyObject { public: MyObject() { std::cout << "MyObject()" << std::endl; } MyObject(const MyObject& other) { std::cout << "MyObject(const MyObject& other)" << std::endl; } MyObject& operator=(const MyObject& other) { std::cout << "operator=(const MyObject& other)" << std::endl; return *this; } }; int main() { MyObject object1; MyObject object2 = object1; MyObject object3(object1); MyObject object4; object4 = object1; }

输出：

MyObject() MyObject(const MyObject& other) MyObject(const MyObject& other) MyObject() operator=(const MyObject& other)

除此之外，我建议阅读什么是三条规则？

You can try this to see the exact behavior:

#include <iostream> class MyObject { public: MyObject() { std::cout << "MyObject()" << std::endl; } MyObject(const MyObject& other) { std::cout << "MyObject(const MyObject& other)" << std::endl; } MyObject& operator=(const MyObject& other) { std::cout << "operator=(const MyObject& other)" << std::endl; return *this; } }; int main() { MyObject object1; MyObject object2 = object1; MyObject object3(object1); MyObject object4; object4 = object1; }

Outputs:

MyObject() MyObject(const MyObject& other) MyObject(const MyObject& other) MyObject() operator=(const MyObject& other)

Apart from that, I recommend reading What is The Rule of Three?