C setjump and longjump

Last Updated : 11 Mar, 2023

“Setjump” and “Longjump” are defined in setjmp.h, a header file in C standard library.

setjump(jmp_buf buf) : uses buf to remember the current position and returns 0.
longjump(jmp_buf buf, i) : Go back to the place buf is pointing to and return i.

C

// C program to demonstrate  
// working of setjmp() and 
// longjmp() 
#include <setjmp.h> 
#include <stdio.h> 
jmp_buf buf; 
void func() 
{ 
    printf("Welcome to GeeksforGeeks\n"); 
  
    // Jump to the point setup by setjmp 
    longjmp(buf, 1); 
  
    printf("Geek2\n"); 
} 
  
int main() 
{ 
    // Setup jump position using buf and return 0 
    if (setjmp(buf)) 
        printf("Geek3\n"); 
    else { 
        printf("Geek4\n"); 
        func(); 
    } 
    return 0; 
}

Output

Geek4
Welcome to GeeksforGeeks
Geek3

The main feature of these functions is to provide a way that deviates from standard call and return sequences. This is mainly used to implement exception handling in C. setjmp can be used like try (in languages like C++ and Java). The call to longjmp can be used like throw (Note that longjmp() transfers control to the point set by setjmp()).