SETJMP(3)

SETJMP(3) | Library Functions Manual | SETJMP(3)

# NAME

`sigsetjmp`, `siglongjmp`, `setjmp`, `longjmp`, `_setjmp`, `_longjmp`, `longjmperror` —
non-local jumps

# LIBRARY

Standard C Library (libc, -lc)

# SYNOPSIS

`#include <setjmp.h>`

int
`sigsetjmp`(sigjmp_buf env, int savemask);

void
`siglongjmp`(sigjmp_buf env, int val);

int
`setjmp`(jmp_buf env);

void
`longjmp`(jmp_buf env, int val);

int
`_setjmp`(jmp_buf env);

void
`_longjmp`(jmp_buf env, int val);

void
`longjmperror`(void);

# DESCRIPTION

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

The corresponding `longjmp`() 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 `longjmp`() functions cannot cause `setjmp`() to return 0; if val is 0, `setjmp`() returns 1 instead.

Pairs of calls may be intermixed, i.e., both `sigsetjmp`() and `siglongjmp`() 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 `longjmp`() routines may not be called after the routine which called the `setjmp`() routines returns.

All accessible objects have values as of the time `longjmp`() 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 `setjmp`()/`longjmp`() function pairs save and restore the signal mask while `_setjmp`()/`_longjmp`() function pairs save and restore only the register set and the stack. (See `sigprocmask`(2).)

The `sigsetjmp`()/`siglongjmp`() 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, `setjmp`()/`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 `sigsetjmp`()/`siglongjmp`() interfaces are preferred for maximum portability.

# ERRORS

If the contents of the env are corrupted or correspond to an environment that has already returned, the `longjmp`() routine calls the routine longjmperror(3). If `longjmperror`() returns, the program is aborted (see abort(3)). The default version of `longjmperror`() prints the message “`longjmp botch`” to standard error and returns. User programs wishing to exit more gracefully should write their own versions of `longjmperror`().

# SEE ALSO

sigaction(2), sigaltstack(2), sigprocmask(2), pthread_sigmask(3), signal(3)

# STANDARDS

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”).

# CAVEATS

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. 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.

June 1, 2008 | NetBSD 10.1