I'm lost at the first line of code:

  char buffer[64];

I was curious about the "Why not printf" section, but I found code I don't understand there, too. For example this admittedly non-working snippet is cited as idiomatic:

  char str[4] = {0};
  int cursor = 0;
  cursor += snprintf(str, sizeof str, "hello ");
  cursor += snprintf(str, sizeof str, "world!");