How to elegantly avoid "condition is always true" warning for this particular kind of for-loop?

Question

Say that we have the following for-loop:

#define UPPER 0U
int i;
for(i = 0; i < UPPER; i++) {
    /* foo */
}

This will produce a W549: condition is always true warning, obviously because we get for(i = 0; i < 0; i++) after macro expansion. In the actual code, UPPER is a pre-compile time parameter (i.e., it is set by some build scripts depending on the target platform etc.) that can take any value from 0 to 255 and thus the loop is not just dead code.

How can I elegantly avoid this warning when UPPER == 0?

Obviously, one can wrap the for-loop in an if-statement:

#define UPPER 0U
if(UPPER != 0U) {
    int i;
    for(i = 0; i < UPPER; i++) {
        /* foo */
    }
}

But that's not what I'd call elegant.

Answer 1

If you don't want to wrap it in code, wrap the code using conditional compilation:

#if UPPER > 0
  int i;
  for(i = 0; i < UPPER; i++) {
      /* foo */
  }
#endif

The elegance stems from:

• No dead code when UPPER is 0.
• Completely portable to any C compiler since 1970-01-01
• Easy to read and understand