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SETJMP(3) Library Functions Manual SETJMP(3)

sigsetjmp, siglongjmp, setjmp, longjmp, _setjmp, _longjmpnon-local jumps

#include <setjmp.h>

sigsetjmp(sigjmp_buf env, int savemask);

siglongjmp(sigjmp_buf env, int val);

setjmp(jmp_buf env);

longjmp(jmp_buf env, int val);

_setjmp(jmp_buf env);

_longjmp(jmp_buf env, int val);

The (), setjmp(), and () functions save their calling environment in env. Each of these functions returns 0.

The corresponding () functions restore the environment saved by the most recent invocation of the respective setjmp() function. They then return so that program execution continues as if the corresponding invocation of the setjmp() call had just returned the value specified by val, instead of 0. The value specified by val must be non-zero; a 0 value is treated as 1 to allow the programmer to differentiate between a direct invocation of setjmp() and a return via longjmp().

Pairs of calls may be intermixed; i.e., both () and () as well as setjmp() and longjmp() combinations may be used in the same program. However, individual calls may not — e.g., the env argument to setjmp() may not be passed to siglongjmp().

The () routines may not be called after the routine which called the setjmp() routines returns.

All accessible objects have values as of the time the () routine was called, except that the values of objects of automatic storage invocation duration that do not have the volatile type and have been changed between the setjmp() invocation and longjmp() call are indeterminate.

The ()/longjmp() function pairs save and restore the signal mask while the ()/() function pairs save and restore only the register set and the stack (see sigprocmask(2)).

The ()/() function pairs save and restore the signal mask if the argument savemask is non-zero. Otherwise, only the register set and the stack are saved.

In other words, ()/longjmp() are functionally equivalent to sigsetjmp()/siglongjmp() when sigsetjmp() is called with a non-zero savemask argument. Conversely, _setjmp()/_longjmp() are functionally equivalent to sigsetjmp()/siglongjmp() when sigsetjmp() is called with a zero-value savemask.

The ()/() interfaces are preferred for maximum portability.


The setjmp() and longjmp() functions conform to ANSI X3.159-1989 (“ANSI C89”). The sigsetjmp() and siglongjmp() functions conform to IEEE Std 1003.1-1990 (“POSIX.1”).

The setjmp() and longjmp() functions first appeared in the Programmer's Workbench (PWB/UNIX).

Historically, on AT&T System V UNIX, the setjmp()/longjmp() functions have been equivalent to the BSD _setjmp()/_longjmp() functions and do not restore the signal mask. Because of this discrepancy, the sigsetjmp()/siglongjmp() interfaces should be used if portability is desired.

Use of longjmp() or siglongjmp() from inside a signal handler is not as easy as it might seem. Generally speaking, all possible code paths between the setjmp() and longjmp() must be signal race safe, as discussed in signal(3). Furthermore, the code paths must not do resource management (such as open(2) or close(2)) without blocking the signal in question, or resources might be mismanaged. Obviously this makes longjmp() much less useful than previously thought.

May 23, 2016 OpenBSD-6.5