C++:not able to understand why compiler not give error to this code and it work properly

class abc
{ int x;
 public:
 开发者_如何学Cabc(){}//default constructor
 abc(int a)
 {
  x=a;
 }
 abc operator++(int a)//code for postfix ++ overloading
 {
  a=x++;
  return a;
 }
 void display()
 {
  cout<<x<<endl;
 }
};

int main()
{
 abc a(12),q;
 q=a++;
 q.display();
 return 0;
}

//code gives no compiling error and working well

The only "question" I can see in here is the return a; because a is an int and the method is declared to return an abc. In this case, the compiler will invoke the abc(int) constructor to construct a new instance of the object for return from the increment operator.

If you change the constructor to be explicit:

explicit abc(int a)
{
 x=a;
}

then you will get an error:

t.cpp: In member function 'abc abc::operator++(int)':
Line 12: error: conversion from 'int' to non-scalar type 'abc' requested
compilation terminated due to -Wfatal-errors.