Question

We know that compiler generates some member functions for user-defined class if that member functions are not defined but used, isn’t it. So I have this kind of code:

class AA
{
};

void main()
{
    AA a;
    AA b(a);
    a = b;
}

This code works fine. I mean no compiler error. But the following code….

class AA
{
    int member1;
    int member2;
};

But this code gives an run time error, because variable “a” is used without being iniltialized!!!

So my question is this: when we instantiate an int, it has a value. So why the default constructer doesn’t work and by using those two int numbers initializes variable “a”??

EDIT: Platform: Win Vista, Compiler: Visual Studio 2008 compiler; Flags: Default

Answer 1

The compiler-synthesised default constructor calls the default constructors for all class members that have constructors. But integers don’t have constructors, and so are not initialised. However, I find it hard to believe that this will cause a run-time error.

To initialise those variables:

class AA {
  public:
     AA() : member1(0), member2(0) {}
  private:
    int member1;
    int member2;
};