longjmp() -- General Function (libc)

Perform a non-local goto
#include <setjmp.h>
int longjmp(env, rval)
jmp_buf env; int rval;

The function call is the only mechanism that C provides to transfer control
between functions.  This mechanism is inadequate for some purposes, such as
handling unexpected errors or interrupts  at lower levels of a program.  To
answer this need, longjmp provides a non-local goto.

longjmp() restores an environment that had been saved by a previous call to
the  function  setjmp().   It returns  the  value  rval  to  the caller  of
setjmp(),  just as  if  the setjmp()  call  had just  returned.  Note  that
longjmp() must  not restore the  environment of a routine  that has already
returned.  The type declaration for jmp_buf is in the header file setjmp.h.
The  environment saved  includes the  program  counter, stack  pointer, and
stack  frame.  These  routines  do not  restore register  variables in  the
environment returned.

Example

For an example of this function, see the entry for setjmp().

See Also

libc,
setjmp(),
siglongjmp()
ANSI Standard, §7.6.2.1
POSIX Standard, §8.1

Notes

Programmers should note that many user-level routines cannot be interrupted
and  reentered safely.   For  that reason,  improper use  of longjmp()  and
setjmp() can result in  the creation of mysterious and irreproducible bugs.
Do not attempt to use longjmp() within an exception handler.

© 2012 by Stephen A. Ness