setjmp(3)						     Library Functions Manual							 setjmp(3)

NAME

       setjmp, _setjmp, longjmp, _longjmp - Saves and restores the current execution context

LIBRARY

       Standard C Library  (libc.a, libc.so) System V Library (libsys5.a, libsys5.so)

SYNOPSIS

       #include <setjmp.h>

       int setjmp(
	       jmp_buf environment);

       void longjmp(
	       jmp_buf environment,
	       int value);

       int _setjmp (
	       jmp_buf environment);

       void _longjmp(
	       jmp_buf environment,
	       int value);

STANDARDS

       Interfaces documented on this reference page conform to industry standards as follows:

       setjmp(), longjmp(): XSH4.2

       _setjmp(), _longjmp(): XSH4.2

       Refer to the standards(5) reference page for more information about industry standards and associated tags.

PARAMETERS

       Specifies  an  address  for  a jmp_buf structure.  Specifies the value you want written to the execution context as the return value of the
       setjmp() or _setjmp() function.	If you specify 0 (zero) in this parameter, the execution context contains a value of 1 as the setjmp()	or
       _setjmp() return value.	See the RETURN VALUES section for more information.

DESCRIPTION

       The setjmp() and longjmp() functions are useful when handling errors and interrupts encountered in low-level functions of a program.

       The  setjmp()  function saves the current stack context and signal mask in the buffer specified by the environment parameter.  You then use
       the buffer in a later call to the longjmp() function. The longjmp() function restores the stack context and signal mask that were saved	by
       the setjmp() function.

       After  the longjmp() function runs, program execution continues as though the corresponding call to the setjmp() function had just returned
       the value of the value parameter.  The function that called the setjmp() function must not have	returned  before  the  completion  of  the
       longjmp() function.

       The _setjmp() and _longjmp() functions operate identically to the setjmp() and longjmp() functions, respectively, except that _setjmp() and
       _longjmp() manipulate only the stack context.  These functions do not restore the signal mask.

       All accessible objects have values at the time longjmp() is called, except for some objects of  automatic  storage  duration.   Objects	of
       automatic storage duration will have indeterminant values if they meet all of the following conditions: They are local to the function con-
       taining the corresponding setjmp() invocation.  They do not have volatile-qualified type.  They are changed between the	setjmp()  and  the
       longjmp() call.

       Because	it  bypasses  the  usual function call and return mechanisms, the longjmp() function executes correctly in contexts of interrupts,
       signals, and any of their associated functions.	However, if the longjmp() function is invoked from a nested signal handler (that is,  from
       a function invoked as a result of a signal raised during the handling of another signal), the behavior is undefined.

NOTES

       [Tru64  UNIX]  For  compatibility,  the	System	V  versions of the setjmp() and longjmp() functions, which are equivalent to _setjmp() and
       _longjmp(), respectively, are also supported.  To use the System V versions of setjmp() and longjmp(),  you  must  link	with  the  libsys5
       library before you link with libc.

CAUTION

       The  results  of  the  longjmp()  function  are undefined in the following situations: The longjmp() function is called with an environment
       parameter that was not previously set by the setjmp() function.	The function that made the corresponding call to the setjmp() function has
       already returned.

       If  the longjmp() function detects one of these conditions, it calls the longjmperror() function. If longjmperror() returns, the program is
       aborted.  The default version of longjmperror() displays an error message to standard error and returns. If you want your program  to  exit
       more gracefully, you can write your own version of the longjmperror() program.

RETURN VALUES

       After  the  longjmp() function is finished executing, program execution continues as though the corresponding call of the setjmp() function
       just returned.  In other words, the execution context saved by the corresponding setjmp() function is in place and execution  continues	at
       the statement immediately following the call to the setjmp() function.

       Part  of  that  execution  context is the return value from the setjmp() function.  When the setjmp() function actually returns (before the
       call to the longjmp() function), that return value is 0 (zero).	When the longjmp() function returns,  the  execution  context  contains  a
       non-zero value as the return value from the setjmp() function.

       The  value  you	specify  in  the value parameter to the longjmp() function is written to the execution context as the return value for the
       setjmp() function.  You cannot cause the execution context to contain a 0 (zero) value for the setjmp() return value.  If you specify 0	in
       the value parameter, the execution context contains a 1 as the setjmp() return value.

RELATED INFORMATION

       Routines: siglongjmp(3), sigsetjmp(3)

       Standards: standards(5) delim off

																	 setjmp(3)