Code:
int CmpFunc(const void* _a, const void* _b)
{
  // you've got to explicitly cast to the correct type
  const float* a = (const float*) _a;
  const float* b = (const float*) _b;

  if(*a > *b) return 1;              // first item is bigger than the second one -> return 1
  else if(*a == *b) return  0;         // equality -> return 0
  else         return -1;         // second item is bigger than the first one -> return -1
}
They use a '_' character as the first character of variable _a, I know this is a way to declare a variable. My question is: what is the advantage of this declaration? Please tell me, provide links or suggest books if any. Thanks !