Thread: Why member initialization?

I don't want to be too much of an annoying newb on all of you 1337 h4x0rz But I have some notes from class, and on the back bottom page there is a little "helpful note" but it was neither explained nor used...

I have talked with fellow classmates about this and have gotten answers, but I am the type of guy who likes to see what a wide variety of people say so I can make better overall judgments... SO.... can you please help explain the following....... (in your own words)

Code:

//
// DO THIS - Member initialization
//
User::User( const RefParam &inParam )
: mPointerMember( new PointerMember( inParam ))
{
	return;
}

//
// DO NOT DO THIS
//
User::User( const RefParam &inParam )
{
	mPointerMember = new PointerMember( inParam );
	return;
}

So like I said.... you're own explainations would be quite appreciated

I dont think there is a big difference in this case. It's not like the PointerMember is getting constructed and then re-assigned, so the two aren't really different, from my knowledge, unlike they would be if PointerMember wasn't a pointer, but instead a reference (it would be illegal), or a value (it would be constructed to default and then assigned).

The only thing I know about this is as follows: You are forced to use the first method in the case of const member variables. They are impossible to initialize any other way. As for anything else, do what feels best for you. Using the initializers lists probably looks cooler but if its going to confuse you or someone else responsible for debugging your code, then go for the second method. Mostly, I think the more experienced programmers will tend to use the first method while newbies will go for the second.

Code:

class MyClass{
    const int iValue;
...
...
...
};

MyClass::MyClass( const int val ) : iValue( val ) // Works!!!
{
}

MyClass::MyClass( const int val )
{
    iValue = val;   // Won't work!!!
}

But in the case of a pointer member, it's only constructing a pointer, not a value object. An extra assignment of a pointer is not really going to do much in terms of run time cost.