c ++函数按值返回

Question

由以下代码混淆，至少应该调用两个构造函数，一个用于funcReturningA中的变量tmp，另一个用于main中的变量a。但输出只是一行：

  带有args的

构造函数

#include <iostream>                                                             
using namespace std;                                                            

class A {                                                                          
    private:                                                                    
            int member;                                                            
    public:                                                                     
            A() {                                                                  
                    cout << "Default constructor" << endl;;                        
            }                                                                      
            A(int member) {                                                        
                    this->member = member;                                         
                    cout << "constructor with args" << endl;                       
            }                                                                      
            A(const A &a) {                                                        
                    cout << "copy constructor by ref" << endl;;                    
            }                                                                      
            A &operator=(const A &a) {                                             
                    cout << "copy assign operator by const ref" << endl;           
            }                                                                      
            A &operator=(A) {                                                      
                    cout << "copy assign operator by value" << endl;               
            }                                                                      
};                                                                                 

A funcReturningA() {                                                               
        A tmp(10);                                                                 
        return tmp;                                                                
}                                                                                  

int main(int argc, char **argv) {                                                  
........                                                                           
        A a = funcReturningA();                                                    
        return 0;                                                                  
}