setjmp(3)               (BSD Compatibility Package)               setjmp(3)


   NAME
         setjmp, longjmp, setjmp, longjmp, sigsetjmp, siglongjmp - non-local
         goto

   SYNOPSIS
         cc [ flag... ] file ... -lucb

         #include <setjmp.h>

         int setjmp(env)
         jmpbuf env;

         longjmp(env, val)
         jmpbuf env;
         int val;

         int setjmp(env)
         jmpbuf env;

         longjmp(env, val)
         jmpbuf env;
         int val;

         int sigsetjmp(env, savemask)
         sigjmpbuf env;
         int savemask;

         siglongjmp(env, val)
         sigjmpbuf env;
         int val;

   DESCRIPTION
         setjmp and longjmp 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.
         A normal call to setjmp returns zero.  setjmp also saves the register
         environment.  If a longjmp call will be made, the routine which
         called setjmp should not return until after the longjmp has returned
         control (see below).

         longjmp restores the environment saved by the last call of setjmp,
         and 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; however, if val were zero, execution would continue
         as if the call of setjmp had returned one.  This ensures that a
         ``return'' from setjmp caused by a call to longjmp can be
         distinguished from a regular return from setjmp.  The calling
         function must not itself have returned in the interim, otherwise
         longjmp will be returning control to a possibly non-existent
         environment.  All memory-bound data have values as of the time


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   setjmp(3)               (BSD Compatibility Package)               setjmp(3)


         longjmp was called.  The CPU and floating-point data registers are
         restored to the values they had at the time that setjmp was called.
         But, because the register storage class is only a hint to the C
         compiler, variables declared as register variables may not
         necessarily be assigned to machine registers, so their values are
         unpredictable after a longjmp.  This is especially a problem for
         programmers trying to write machine-independent C routines.

         setjmp and longjmp save and restore the signal mask (see
         sigsetmask(2)), while setjmp and longjmp manipulate only the C
         stack and registers.  If the savemask flag to sigsetjmp is non-zero,
         the signal mask is saved, and a subsequent siglongjmp using the same
         env will restore the signal mask.  If the savemask flag is zero, the
         signal mask is not saved, and a subsequent siglongjmp using the same
         env will not restore the signal mask.  In all other ways, setjmp and
         sigsetjmp function in the same way that setjmp does, and longjmp and
         siglongjmp function in the same way that longjmp does.

         None of these functions save or restore any floating-point status or
         control registers.

   EXAMPLE
         The following code fragment indicates the flow of control of the
         setjmp and longjmp combination:

               function declaration
               ...
                     jmpbuf     myenvironment;
                     ...
                     if (setjmp(myenvironment))  {
                       /* register variables have unpredictable values */
                           code after the return from longjmp
                           ...
                     } else {
                       /* do not modify register vars in this leg of code */
                           this is the return from setjmp
                           ...
                     }

   SEE ALSO
         cc(1), signal(3), sigsetmask(3), sigvec(3).

         cc(1), signal(2), setjmp(3C) in the Programmer's Reference Manual.

   BUGS
         setjmp does not save the current notion of whether the process 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.





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   setjmp(3)               (BSD Compatibility Package)               setjmp(3)


         On some systems setjmp also saves the register environment.
         Therefore, all data that are bound to registers are restored to the
         values they had at the time that setjmp was called.  All memory-bound
         data have values as of the time longjmp was called.  However, because
         the register storage class is only a hint to the C compiler,
         variables declared as register variables may not necessarily be
         assigned to machine registers, so their values are unpredictable
         after a longjmp.  When using compiler options that specify automatic
         register allocation (see cc(1V)), the compiler will not attempt to
         assign variables to registers in routines that call setjmp.

         longjmp never causes setjmp to return zero, so programmers should not
         depend on longjmp being able to cause setjmp to return zero.








































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