Thread: macro or function

> is ait better to use a macro than a function since function adds up to code size while a macros does not
Macros do add to the code size - a lot more than a function would for a complex macro. If you had a 10 line macro, and you used it 10 times, there would be an additional 100 lines of compiled code.

As a function, there would be 10 lines of code, plus a further 10 to call it (20 in total).

Technically (and superficially), macros are faster than a function because you don't actually have a function call. However, when you mix in cache and code bloat, the issue is far more complex. In addition, C99 introduces inline functions, which are as fast as macros, but with all the benefits of predictable evaluation and type checking of arguments.

You're only going to notice the cost of that function call if the function is a) very small, and b) called millions of times.

Take your register example - it may look nice "as is", but if you want to say validate the arguments (to prevent bad values being written to certain registers), you pretty much need a function at that point. You also need it to be a function if you're to have any real chance of profiling the code prior to optimisation.

Personally, I go for functions for everything until I know that a macro would be an improvement.

I'm sticking to my previous comments

While you're at it, consider this

Code:

#include <stdio.h>
#undef max
#define max(a,b) a>b?a:b
int main ( ) {
    int a = 1, b = 1;
    char *foo = max("hello","world");
    int c = max(a++,b++);
    printf( "a=%d, b=%d, c=%d, foo=%s\n", a, b, c, foo );
    return 0;
}