Can a C macro contain temporary variables?

Question

I have a function that I need to macro\'ize. The function contains temp variables and I can\'t remember if there are any rules about use of temporary variables in macro subs

Answer 1

First, I strongly recommend inline functions. There are very few things macros can do and they can't, and they're much more likely to do what you expect.

One pitfall of macros, which I didn't see in other answers, is shadowing of variable names.
Suppose you defined:

#define A(x) { int temp = x*2; printf("%d\n", temp); }

And someone used it this way:

int temp = 3;
A(temp);

After preprocessing, the code is:

int temp = 3;
{ int temp = temp*2; printf("%d\n", temp); }

This doesn't work, because the internal temp shadows the external.
The common solution is to call the variable __temp, assuming nobody will define a variable using this name (which is a strange assumption, given that you just did it).