Passing, AND modifying object values (passing const... discards qualifiers error)

**Iconate** · 04-04-2010

So I am trying to pass an object to a function and access its methods, some of which modify its values. However, I haven't done this before, and I was following this example

Use & to get object address : object pointer « Class « C++ Tutorial

but since I keep getting

passing `...' as `this' argument of `...' discards qualifiers

I realize I am not supposed to be using "const", since that Object is not remaining constant. (vs, the example where they dont actually change the values)

What should a function be, which is receiving an object in order to be modified

If any examples could be provided or a link to another tutorial, that would help me out A LOT, thanks

**laserlight** · 04-04-2010

What exactly is the code that you tried?

**Iconate** · 04-04-2010

Code:

const Target *  const animateTarget( const Target *  const tar){

...
tar->setValue(something)
....
}

**laserlight** · 04-04-2010

Well, the code example in the tutorial that you linked to compiles for me without even a warning. So, you should post the smallest and simplest example that demonstrates the problem, not a fragment that could be correct, or could be wrong, depending on what you don't show.

**anon** · 04-04-2010

Quite obviously you shouldn't insist that the object is const if you want to modify it (by calling non-const methods).

Code:

const Target *  const animateTarget( Target *  const tar){
    ...
    tar->setValue(something)
    ....
}

If the intention was really not to modify it, then you shouldn't be calling setValue() (or that method should be marked "const", which is hard to believe it is).

**EVOEx** · 04-04-2010

@laserlight: I don't believe for one second you didn't immediately know what the problem was.
Actually, I usually refuse to answer badly formulated questions as well, but I consider this one to be okay. I mean, even from his first post you can easily tell he tried to call a non-const function on a const object.

**Elysia** · 04-04-2010

Pointing out what the problem is as opposed to where the problem is sometimes just isn't helpful.
Pointing out where and why is even more helpful.

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