setjmp(3C) setjmp(3C)
NAME
setjmp(), longjmp(), sigsetjmp(), siglongjmp() - non-local goto
SYNOPSIS
DESCRIPTION
and are useful for dealing with errors and interrupts encountered in a low-level subroutine of a program. They exist in three variant
forms: and and and Unless indicated otherwise, references to and apply to all three versions.
saves its stack environment in
env (whose type, is defined in the header file) for later use by It returns the value
restores the environment saved by the last call of
with the corresponding env argument. After is completed, program execution continues as if the corresponding call
of (which must not itself have returned in the interim) had just returned the value val. cannot cause to return
the value If is invoked with a second argument of returns All accessible data values are valid as of the time is
called.
Upon the return from a call caused by a the values of any non-static or non-volatile local variables belonging to the routine from which
was called are undefined. Code which depends on such values is not guaranteed to be portable.
Variant Forms
The following functions behave the same as and except in the handling of the process' signal mask (see sigaction(2)). This distinction is
only significant for programs which use and/or
These always save and restore the signal mask.
These never manipulate the signal mask.
Saves the signal mask of the calling thread if and only if
savemask is non-zero.
Restores the signal mask if and only if it is saved by
Programming Considerations
If a is executed and the environment in which the is executed no longer exists, errors can occur. The conditions under which the environ-
ment of the no longer exists include exiting the procedure that contains the call, and exiting an inner block with temporary storage (such
as a block with declarations in C or a statement in Pascal). This condition might not be detectable, in which case the occurs and, if the
environment no longer exists, the contents of the temporary storage of an inner block are unpredictable. This condition might also cause
unexpected process termination. If the procedure has been exited the results are unpredictable.
Passing a pointer to a buffer not created by passing a pointer to a buffer not created by either or passing a pointer to a buffer not cre-
ated by or passing any of these three functions a buffer that has been modified by the user, can cause all the problems listed above, and
more.
Some implementations of Pascal support a ``try/recover'' mechanism, which also creates stack marker information. If a operation occurs in
a scope which is nested inside a try/recover, and the corresponding is not inside the scope of the try/recover, the recover block will not
be executed and the currently active recover block will become the one enclosing the if one exists.
WARNINGS
A call to to leave the guaranteed stack space reserved by might remove the guarantee that the ordinary execution of the program will not
extend into the guaranteed space. It might also cause the program to forever lose its ability to automatically increase the stack size,
and the program might then be limited to the guaranteed space.
The result of using within an expression can be unpredictable.
If is called even though env was never primed by a call to or when the last such call was in a function that has since returned, total
chaos is guaranteed.
The effect of a call to where the initialization of the argument was not performed in the calling thread is undefined. The effect of a
call to where the initialization of the argument was not performed in the calling thread is undefined.
The contents of the buffer are architecture and compilation environment specific. Thus, objects built using these functions may not be
supported across architectures.
AUTHOR
was developed by AT&T and HP.
SEE ALSO
sigaction(2), sigblock(2), signal(5), sigprocmask(2), sigsetmask(2), sigspace(2), sigsuspend(2), thread_safety(5).
STANDARDS CONFORMANCE
setjmp(3C)