The use of const and &

Let's say i create a class:

Code:

class myClass { ... };

I'm used to passing it like this for read-only functions:

Code:

const myClass& aName

But i realised that some problems come up, so i figured this:

Code:

const myClass& aName // for using its member variables
const myClass aName // for using it directly

Could you tell me if there is a benefit of using this method, if it is correct?

I'm unclear on what your distinction between "using its member variables" and "using it directly" is.

Also, what kind of problems?

Originally Posted by Sipher

Could you tell me if there is a benefit of using this method, if it is correct?

Use the reference whenever you pass a class to a function. It prevents the class from being copied when it's passed to a function.

Originally Posted by Sipher

But i realised that some problems come up

Problems you say? We often like to help with problems. What were those problems?

Don't ask us what we think of your solution, ask us what our solution would be.

I'm having a hard time imagining a situation where you'd pass a const instance rather than a const reference. If it's const, then it cannot be changed and the question of whether it should be copied or not is moot.

Code:

class aClass
{
   public:
       int a;
       
       const aClass Sum(const aClass& c)
       {
          aClass Result;
    
          Result.a = a + c.a;

          return Result;
       }
 
       void SumTo(const aClass c)
       {
          *this = Sum(c);
       }
   
};

By saying 'using its member variables' i mean using the Sum member functions
By saying 'using it directly' i mean using the SumTo

This is of course a very rough example, but that's the idea.

The compiler, when i pass an aClass through another struct or class instance, throws an error that 'this' function discards qualifiers. What does it mean?

Many thanks for the interest guys!

For the error, it means you're calling a non-const member function on a const object.
Ie, consider you have
const aClass& myclass
And do
myclass.Sum(...);

This would result in an error because the function is not guaranteeing that it won't change the function's state, which is what const is all about.
Adding a "const" keyword after the function (say Sum), will fix that.