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

C macros are only (relatively simple) textual substitutions.

So the question you are maybe asking is: can I create blocks (also called compound statements) in a function like in the example below?

void foo(void)
{
    int a = 42;
    {   
        int b = 42;
        {
            int c = 42; 
        } 
    }
}

and the answer is yes.

Now as @DietrichEpp mentioned it in his answer, if the macro is a compound statement like in your example, it is a good practice to enclose the macro statements with do { ... } while (0) rather than just { ... }. The link below explains what situation the do { ... } while (0) in a macro tries to prevent:

http://gcc.gnu.org/onlinedocs/cpp/Swallowing-the-Semicolon.html

Also when you write a function-like macro always ask yourself if you have a real advantage of doing so because most often writing a function instead is better.