All of the signal blocking functions use a data structure called a
signal set to specify what signals are affected. Thus, every
activity involves two stages: creating the signal set, and then passing
it as an argument to a library function.
These facilities are declared in the header file signal.h.
— Data Type: sigset_t
The sigset_t data type is used to represent a signal set.
Internally, it may be implemented as either an integer or structure
type.
For portability, use only the functions described in this section to
initialize, change, and retrieve information from sigset_t
objects—don't try to manipulate them directly.
There are two ways to initialize a signal set. You can initially
specify it to be empty with sigemptyset and then add specified
signals individually. Or you can specify it to be full with
sigfillset and then delete specified signals individually.
You must always initialize the signal set with one of these two
functions before using it in any other way. Don't try to set all the
signals explicitly because the sigset_t object might include some
other information (like a version field) that needs to be initialized as
well. (In addition, it's not wise to put into your program an
assumption that the system has no signals aside from the ones you know
about.)
— Function: int sigemptyset (sigset_t *set)
This function initializes the signal set set to exclude all of the
defined signals. It always returns 0.
— Function: int sigfillset (sigset_t *set)
This function initializes the signal set set to include
all of the defined signals. Again, the return value is 0.
— Function: int sigaddset (sigset_t *set, int signum)
This function adds the signal signum to the signal set set.
All sigaddset does is modify set; it does not block or
unblock any signals.
The return value is 0 on success and -1 on failure.
The following errno error condition is defined for this function:
EINVAL
The signum argument doesn't specify a valid signal.
— Function: int sigdelset (sigset_t *set, int signum)
This function removes the signal signum from the signal set
set. All sigdelset does is modify set; it does not
block or unblock any signals. The return value and error conditions are
the same as for sigaddset.
Finally, there is a function to test what signals are in a signal set:
— Function: int sigismember (const sigset_t *set, int signum)
The sigismember function tests whether the signal signum is
a member of the signal set set. It returns 1 if the signal
is in the set, 0 if not, and -1 if there is an error.
The following errno error condition is defined for this function:
EINVAL
The signum argument doesn't specify a valid signal.
Published under the terms of the GNU General Public License
