c++ copy constructor, operator=

参考Copy constructors, assignment operators, and exception safe assignment

1. copy constructor

The copy constructor is called whenever an object is initialized from another object of the same type, which includes

1. initialization, T a = b; or T a(b);, where b is of type T
2. function argument passing: f(a);, where a is of type T and f is void f(T t)
3. function return: return a; inside a function such as T f(), where a is of type T, which has no move constructor.

此外，看一个例子

#include<iostream>using namespace std;class MyClass {public:    int data1_;    int data2_;    MyClass() {        cout << "Default constructor..." << endl;    }    MyClass(int x, int y) : data1_(x), data2_(y) {        cout << "Constructor..." << endl;    }    MyClass(const MyClass& other) : data1_(other.data1_), data2_(other.data2_) {        cout << "Copy Constructor..." << endl;    }    MyClass& operator=(const MyClass& other) {        cout << "operator = ...." << endl;        data1_ = other.data1_;        data2_ = other.data2_;        return *this;    }    void print() const {        cout << "data1: " << data1_ << ", data2: " << data2_ << endl;    }};int main() {    MyClass c1(1, 2);  //should call constructor    MyClass c2 = c1;  //will not call default constructor first, but call copy constructor.    c2.data1_ = 1000;    c1.print();  //should not change, should print "data1: 1, data2: 2"    c2 = c1;  //should call operator =, not copy constructor    return 0;}