setjump() and longjump() in C

In this section, we will see what are the setjump and longjump in C. The setjump() and longjump() is located at setjmp.h library. The syntax of these two functions is like below.

setjump(jmp_buf buf) : uses buf to store current position and returns 0.
longjump(jmp_buf buf, i) : Go back to place pointed by buf and return i.

These are used in C for exception handling. The setjump() can be used as try block, and longjump() can be used as throw statement. The longjump() transfers control the pointe which is pointed by setjump().

Here we will see how to print a number 100 times without using recursion, loop, or macro expansion. Here we will use the setjump() and longjump() functions to do that.

Example

#include <stdio.h>
#include <setjmp.h>
jmp_buf buf;
main() {
   int x = 1;
   setjmp(buf); //set the jump position using buf
   printf("5"); // Prints a number
   x++;
   if (x <= 100)
      longjmp(buf, 1); // Jump to the point located by setjmp
}

Output

5555555555555555555555555555555555555555555555555555555555555555555555555555
555555555555555555555555