a question on function declaration

[winecoding]

In the following class definition:

class X{ 
      // ...
      int m1( );
      int m2( ) const;
}

what is the difference between function m1 and m2, or what is affected by adding a const to the declaration of m2?

[Intrexa]

A constant function does not modify the object for which it was called.

[Bazzy]

If you have a const object/reference to type X you can only call const methods.
The const qualifier can be used to overload a method

class X{ 
      // ...
      int m( ); // called by non-const objects
      int m( ) const; // called by const objects
};