Converting the GNU case range extension to standard C

Question

The GNU case range extension allows case ranges in switch statements:

switch (value) {
    case 1 ... 8:
        printf(\"Hello, 1 to 8\\n\");
        break;         


        

Answer 1

Alternatively, since the numbers are adjacent to each other, you can do a manual optimization of the switch-case.

typedef void(*func_t)(void);

#define CASES_N 9

void func0 (void)
{
  printf("Hello, 0\n");
}

void func1 (void)
{
  printf("Hello, 1 to 8\n");
}

static const func_t execute [CASES_N] =
{
  &func0,
  &func1,
  &func1,
  &func1,
  &func1,
  &func1,
  &func1,
  &func1,
  &func1
};

int main()
{
  if(what < CASES_N)
  {
    execute[what]();
  }
  else
  {
    printf("Hello, default\n");
  }
}

This code is basically the same as a compiler-optimized switch-statement.