Returning multiple values from a C function

Question

Important: Please see this very much related question: Return multiple values in C++.

I\'m after how to do the same thing in ANSI C? Would you use a

Answer 1

The fastest Q&D way that I can think of is to pass the values on a global object, this way you skip the stack operation just keep in mind that it won't be thread safe.

Answer 2

I think that when you return a struct pointer, you probably need to manually find some memory for that. Addresses in parameter list are allocated on the stack, which is way faster.

Answer 3

Keep in mind that sometimes is faster to pass parameters by value and update on return (or make local copies on the stack) than by reference... This is very evident with small structures or few parameters and lots of accesses.

Answer 4

Returning a local copy of the structure is bad because if the struct was declared as non-static inside the function, it becomes null and void once you exit the function.

And to all the folks suggesting references, well the OP did say "C," and C doesn't have them (references).

And sweet feathery Jesus, can I wake up tomorrow and not have to see anything about the King of Flop on TV?

Answer 5

You have described the two possible solutions and your perceived performance constraint. Where you go from here is really up to you - we don't have enough information to make an informed judgement.

Answer 6

As Neil says, you need to judge it for yourself.

To avoid the cost of passing anything, use a global. Next best is a single structure passed by pointer/reference. After that are individual pointer/reference params.

However, if you have to pack data into the structure and then read it back out after the call, you may be better off passing individual parameters.

If you're not sure, just write a bit of quick test code using both approaches, execute each a few hundred thousand times, and time them to see which is best.