SETJMP

Section: C Library Functions (3)
Updated: January 9, 1986
Index Return to Main Contents

NAME

setjmp, longjmp - non-local goto

SYNOPSIS

#include <setjmp.h>

setjmp(env)
jmp_buf env;

longjmp(env, val)
jmp_buf env;

_setjmp(env)
jmp_buf env;

_longjmp(env, val)
jmp_buf env;

DESCRIPTION

These routines are useful for dealing with errors and interrupts encountered in a low-level subroutine of a program.

Setjmp saves its stack environment in env for later use by longjmp. It returns value 0.

Longjmp restores the environment saved by the last call of setjmp. It then returns in such a way that execution continues as if the call of setjmp had just returned the value val to the function that invoked setjmp, which must not itself have returned in the interim. All accessible data have values as of the time longjmp was called.

Setjmp and longjmp save and restore the signal mask sigmask(2), while _setjmp and _longjmp manipulate only the C stack and registers.

ERRORS

If the contents of the jmp_buf are corrupted, or correspond to an environment that has already returned, longjmp calls the routine longjmperror. If longjmperror returns the program is aborted. The default version of longjmperror prints the message ``longjmp botch'' to standard error and returns. User programs wishing to exit more gracefully can write their own versions of longjmperror.