====== longjmp ======
<code c>
void longjmp (jmp_buf env, int val);
</code>

==== description of longjmp ====
get program state from the stack, useful for debugging.

<code c>
#include <stdio.h>
#include <setjmp.h>

void testit(int);
jmp_buf program_state;

static int count;
void testit(int count) {

   count++; // set counter +1 but it will never reach 2
   printf("count is now %i\n", count);
   }

int main(void) {
   count = 0;
   printf("count starts with: %i\n", count);

   if(setjmp(program_state) == 0) {
       printf("save program state in the stack\n");
       testit(count);
   }
   else {
        printf("callback with longjmp\n");
        testit(count);
        testit(count);
        return 0;
   }

   testit(count);
   longjmp(program_state,1);
   printf("never called\n");
   testit(count);

   return 0;
}

</code>

===== output of longjmp c example =====
    count starts with: 0
    save program state in the stack
    count is now 1
    count is now 1
    callback with longjmp
    count is now 1
    count is now 1