setjmp(3C) COMPATIBILITY FUNCTIONS setjmp(3C)
NAME
setjmp, longjmp - non-local goto
SYNOPSIS
#include <setjmp.h>
int setjmp (jmp_buf env);
void longjmp (jmp_buf env, int val);
DESCRIPTION
These functions are useful for dealing with errors and
interrupts encountered in a low-level subroutine of a pro-
gram.
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.
EXAMPLE
#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();
Last change: C Programming Language Utilities 1
setjmp(3C) COMPATIBILITY FUNCTIONS setjmp(3C)
/* 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
SEE ALSO
signal(2), sigsetjmp(3C).
NOTES
If longjmp is called even though env was never primed by a
call to setjmp, or when the last such call was in a function
that has since returned, absolute chaos is guaranteed.
Last change: C Programming Language Utilities 2