BSD 2.11 - man page for _setjmp (bsd section 3)
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setjmp, longjmp - non-local goto
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.
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.
sigvec(2), sigstack(2), signal(3)
On the PDP-11, longjmperror is called as _ljerr. This difference stems from the limited
name size of the PDP-11 that requires all external names to be unique within the first
seven characters. However, <setjmp.h> automatically translates longjmperror to ljerror
and should be included before any definition longjmperror.
The PDP-11 implementation also contains a subtle bug that occurs when a routine containing
a setjmp has register variables. The bug sometimes causes those variables to be given
invalid values when a longjmp is made back to the routine. Register variables should
therefore be avoided in routines containing setjmps.
And finally, _longjmp may sometimes die fatally. Sorry.
4th Berkeley Distribution January 9, 1986 SETJMP(3)
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