此代码中将调用哪个构造函数或赋值运算符？

Question

The output is

Constructor called
20

When I am adding a copy-constructor, it is giving error " invalid initialization of non-const reference of type 'Foo&' from an rvalue of type 'Foo' "

  #include <iostream>
  using namespace std;

  class Foo
  {

  int a;
  public:
    Foo(int a)
    {
        this->a =a;
        cout<<"Constructor called\n";
    }
    void operator=(Foo f)
    {
        this->a = a;
        cout<< "Assignment operator called";
    }
    void show()
    {
        cout<<this->a<<endl;
    }

  };


  int main() 
  {
    // your code goes here
    Foo F1 = static_cast<Foo>(20);
    F1.show();
    return 0;
  }

Answer 1

There is no assignment in the code you posted. This:

  Foo F1 = static_cast<Foo>(20);

is alternate syntax for copy construction, and is an initialisation, not an assignment.

Your problem with the copy constructor is probably caused by you defining it as

  Foo( Foo & f );

which prevents it from binding to temporary values. It should be:

  Foo( const Foo & f );