Re: Newbie Question: Why can't operator+ be constant?

Hi all,

I am currently learning C++ and was wondering if I could steal a few
minutes of your valuable time to answer a quick question.

I am using Sams teach yourself C++ in 21 days by Jesse Liberty (
misleading title - I've been going through it for 3 weeks and am only on
chapter 16. :)

In chapter 16, a small simple string class is declared with a
String operator+( const String & rhs ) function.

The string class is then used as a class member ( class Employee )to hold
names of individuals.
The employee class has a member function const String & GetName() which
returns a reference to the string class.

What I don't understand is that the book states that the GetName()
function cannot be used as below:

String names = employeeOne.GetName() + employeeTwo.GetName();

"This is because you cannot call operator+ on a constant object because
it changes the object it is called on"

I really can't understand how this is the case, as my operator+ function
doesn't change the object at all, except to create and return a temporary
string which then falls out of scope ( does this count as changing the
object? )

The code of the operator+ function is below for reference:

String String::operator+( const String & rhs )
{
  int totalLength = itsLength + rhs.GetLength();
  String temp(totalLength);
  int i, j;
  for ( i =0; i < itsLength; i++ )
    temp[i] = itsString[i];
  for ( j = 0; j < rhs.GetLength(); j++,i++ )
    temp[i] = rhs[j];
  temp[totalLength] = '\0';
  return temp;
}

Any help would be greatly appreciated.