Question

Here is my code :

class X
{
public:
  X():_x(5){}

  void GetVal(int & oVal)
  {
    oVal = _x;
  }

 private:
  int _x;

};

class Y
{
public:
  X * const GetX()
  {
    return &_x;
  }
private:
  X _x;
};

int main()
{
  Y y;
  X * p = y.GetX();
  int * pInt = new int[2];
 p->GetVal(pInt[0]);
}

In the last line of main, I get an error

Incorrect access of a member from const-qualified function

This error is observed only when the code is compiled on a sun solaris system and doesn’t happen on windows or aix system. Any idea why?

Also the strangest thing is that the error is gone if I replace pInt[0], with a simple integer (int a = 0; p->GetVal(a))

Answer 1

The const in X * const GetX() will be ignored, because the result of the function call is an rvalue and rvalues of non class type cannot be const according to c++ const member function that returns a const pointer.. But what type of const is the returned pointer?.

Are you sure you didn’t mean to write:

const X * GetX() const
{
  return &_x;
}

that is, you change it from returning a constant pointer to variable date into a variable pointer to constant data, and you declare GetX() to be a constant member function, that is a member function that can be used on constant instances of Y: const Y y;

Furthermore in class X, you can change GetVal() to

void GetVal(int & oVal) const
{
  oVal = _x;
}