setjmp, _setjmp, longjmp, _longjmp - Save and restores the
current execution context
#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 );
Standard C Library (libc)
System V Library (libsys5.a, libsys5.so)
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.
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.
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 containing 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.
[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.
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.
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.
Routines: siglongjmp(3), sigsetjmp(3)
Standards: standards(5)
setjmp(3)
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