setjmp(3C)                                             setjmp(3C)



NAME
     setjmp, longjmp - non-local goto

SYNOPSIS
     #include <setjmp.h>

     int setjmp (env)
     jmp_buf env;

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

SYNOPSIS (4.2BSD)
     int _setjmp (env)
     jmp_buf env;

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

DESCRIPTION
     These functions are useful for dealing with errors and
     interrupts encountered in a low-level subroutine of a pro-
     gram.

     setjmp saves its stack environment in env (whose type,
     jmp_buf, is defined in the <setjmp.h> header file) for later
     use by longjmp.  It returns the value 0.

     Longjmp restores the environment saved by the last call of
     setjmp with the corresponding env argument.  After longjmp
     is completed, program execution continues as if the
     corresponding call of setjmp (the caller of which must not
     itself have returned in the interim) had just returned the
     value val.  All accessible data had values as of the time
     longjmp was called.

     In the att universe, longjmp cannot cause setjmp to return
     the value 0.  If longjmp is invoked with a second argument
     of 0, setjmp will return 1.  Not so in the ucb universe.  If
     longjmp is invoked with a second argument of 0, setjmp will
     return 0.

     In the ucb universe, setjmp and longjmp save and restore the
     signal mask sigsetmask(2), while _setjmp and _longjmp mani-
     pulate only the C stack and registers.

SEE ALSO
     sigsetjmp(3C), signal(2), sigstack(2), sigvec(2).





Page 1                        CX/UX Programmer's Reference Manual

setjmp(3C)                                             setjmp(3C)



WARNING
     If longjmp is called even though env was never primed by a
     call to setjmp, or when the last such call was in a function
     which has since returned, absolute chaos is guaranteed.

     setjmp does not save the current notion of whether the pro-
     cess is executing on the signal stack.  The result is that a
     longjmp to some place on the signal stack leaves the signal
     stack state incorrect.

     When compiled with the hc(1) C compiler, variables of
     automatic storage duration which are local to the function
     making a setjmp call may have indeterminate values when
     longjmp is called, if the variables are not typed volatile.









































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