Best practice for compute the function return value

Question

Often I built functions, in C, that checks some parameters and return an error code.

Which is the best approach to stop the values checking when I found an error?

Answer 1

I tend to use a mix of the two styles, with 2nd style (multiple returns) before, and (perhaps) the first style (local variable to be returned later) afterwards.

The rationale is: "multiple returns" is definitive. It can/should be used when there is something absolutely wrong about the parameters passed, or some other unrecoverable condition.
The "local variable" style, instead, allows to write code that can modify the return value even more than once. It tends to produce code that means "let's start by supposing failure; but if everything is ok, then I will rewrite the result as OK". Or the contrary: "assume OK; if anything goes wrong set the result as failure". And in between of these steps, there still can be other returns!

As last thought... I would say that the right style depends on the situation, never assume one is always right and the other is always wrong.