cpp - int & function() question

[tecknophreak]

i'm working with some cpp and i ran across a function such as:

int & function() { return x };

what does this do? it doesn't seem to work like
function(int &x)

it seems the same as
int function() { return x }

[bwkaz]

I'm guessing that x is a private member of a class that function() is a public member of?

The reason it's returned as a reference is so that after the call, you can change x:

int & my_x = object.function();

my_x = 75;

cout << object.function();This should print 75.

[tecknophreak]

well, that seems to be it. although i'm not sure what this guy's doing. he's using it to reference a member of a structure. i can't seem to understand the benefit, with exception that it'll make the line(code) shorter

[bwkaz]

Yeah, I wouldn't think there would be very many places where it'd be useful -- normally, you'd have a "getter" function that returned a copy, and a "setter" function that took whatever and set the member to that. Whatever... at least you know what it does...

[Energon]

Actually, what you'd do is return a constant reference. Returning copies is bad unless it's a primitive type. Returning a constant reference says "I'm giving you a reference, but you can't modify the data", which is what you want. If they try putting it into a non-constant variable, it'll make the copy instead.

The general rule of thumb is that if you want to allow modification, use a pointer, if you don't, use a constant reference. If it's a primitive type that you don't want modified, just return a copy. That "rule" goes for both returning values and passing values to a function.

[bwkaz]

Yeah, but these are int's... ;)

Actually, you're right, and no, I wasn't thinking that far. It's just a coincidence that this example was a primitive.