Question

I use macros to code unrolled loops like this: (silly example)

#define foreach_small_prime(p, instr) {   \
  int p;                                  \
  p = 2; instr;                           \
  p = 3; instr;                           \
  p = 5; instr;                           \
  p = 7; instr;                           \
}

foreach_small_prime(pp, cout << pp);

int sum = 0;
foreach_small_prime(pp, {
  sum += pp;
  if (sum >= 10) cout << sum << endl;
});

But in some cases I might use for construct:

#define foreach_small_even(ii) for(int ii = 0; ii < 20; ii += 2)

int sum = 0;
foreach_small_even(pp) {
  sum += pp;
  if (sum >= 10) cout << sum << endl;
}

I like this macros because I can pass a variable name as a parameter.

Question: Is there a way to define loop like the first one in a for-like syntax like the second macro?

Answer 1

You could check out the Boost preprocessor library. It can do all sorts of looping things. The syntax isn’t great, but I believe it works. I have not used it myself, however.