setjmp(3C)

Synopsis

   #include <setjmp.h>
   

   int setjmp (jmp_buf env);
   

   void longjmp (jmp_buf env, int val);
   

   void _longjmp(jump_buf env, int val);
   

   int _setjmp (jmp_buf env);

Description

setjmp saves its stack environment in env (whose type, jmp_buf, is defined in the <setjmp.h> header file) for later use by longjmp. It returns the value 0.

longjmp restores the environment saved by the last call of setjmp with the corresponding env argument. After longjmp is completed, program execution continues as if the corresponding call of setjmp had just returned the value val. (The caller of setjmp must not have returned in the interim.) longjmp cannot cause setjmp to return the value 0. If longjmp is invoked with a second argument of 0, setjmp will return 1. At the time of the second return from setjmp, all external and static variables have values as of the time longjmp is called (see example). The values of register and automatic variables are undefined.

Register or automatic variables whose value must be relied upon must be declared as volatile.

_longjmp and _setjmp are identical to longjmp and setjmp, except that they do not manipulate the signal mask.

Usage

#include <stdio.h>
#include <stdlib.h>
#include <setjmp.h>

jmp_buf env;
int i = 0;

main ()
{
    void exit();

    if(setjmp(env) != 0) {
       (void) printf("value of i on 2nd return from setjmp: %d\n", i);
       exit(0);
    }
    (void) printf("value of i on 1st return from setjmp: %d\n", i);
    i = 1;
    g();
    / NOTREACHED /
}

g()
{
    longjmp(env, 1);
    / NOTREACHED /
}

If the a.out resulting from this C language code is run, the output will be:

   value of i on 1st return from setjmp: 0
   value of i on 2nd return from setjmp: 1

References

Notices