I wrote the following to try and illustrate understand what's going on:
#include <iostream> using namespace std; class myClass { public: myClass(int x) { this -> x = x; cout << "int constructor called with value x = " << x << endl; } myClass(const myClass& mc) { cout << "copy constructor called with value = " << mc.x << endl; x = mc.x; } myClass & operator = (const myClass & that) { cout << "assignment called" << endl; if(this != &that) { x = that.x; } return *this; } private: int x; }; int main() { myClass x(3); myClass y = myClass(3); } When I compile and run this code I get the following output:
$ ./a.out int constructor called with value x = 3 int constructor called with value x = 3 This would seem to indicate that there is no difference between the two calls made in the main function, but that would be wrong. As litblitb pointed out, the copy constructor must be available for this code to work, even though it gets elided in this case. To prove that, just move the copy constructor in the code above to the private section of the class definition. You should see the following error:
$ g++ myClass.cpp myClass.cpp: In function ‘int main()’: myClass.cpp:27: error: ‘myClass::myClass(const myClass&)’ is private myClass.cpp:37: error: within this context Also note that the assignment operator is never called.
