GNU Info

(libc.info)Sigaction Function Example

---

Next: Flags for Sigaction Prev: Signal and Sigaction Up: Signal Actions

---

Enter node , (file) or (file)node

`sigaction' Function Example
----------------------------

   In Note: Basic Signal Handling, we gave an example of establishing
a simple handler for termination signals using `signal'.  Here is an
equivalent example using `sigaction':

     #include <signal.h>
     
     void
     termination_handler (int signum)
     {
       struct temp_file *p;
     
       for (p = temp_file_list; p; p = p->next)
         unlink (p->name);
     }
     
     int
     main (void)
     {
       ...
       struct sigaction new_action, old_action;
     
       /* Set up the structure to specify the new action. */
       new_action.sa_handler = termination_handler;
       sigemptyset (&new_action.sa_mask);
       new_action.sa_flags = 0;
     
       sigaction (SIGINT, NULL, &old_action);
       if (old_action.sa_handler != SIG_IGN)
         sigaction (SIGINT, &new_action, NULL);
       sigaction (SIGHUP, NULL, &old_action);
       if (old_action.sa_handler != SIG_IGN)
         sigaction (SIGHUP, &new_action, NULL);
       sigaction (SIGTERM, NULL, &old_action);
       if (old_action.sa_handler != SIG_IGN)
         sigaction (SIGTERM, &new_action, NULL);
       ...
     }

   The program just loads the `new_action' structure with the desired
parameters and passes it in the `sigaction' call.  The usage of
`sigemptyset' is described later; see Note: Blocking Signals.

   As in the example using `signal', we avoid handling signals
previously set to be ignored.  Here we can avoid altering the signal
handler even momentarily, by using the feature of `sigaction' that lets
us examine the current action without specifying a new one.

   Here is another example.  It retrieves information about the current
action for `SIGINT' without changing that action.

     struct sigaction query_action;
     
     if (sigaction (SIGINT, NULL, &query_action) < 0)
       /* `sigaction' returns -1 in case of error. */
     else if (query_action.sa_handler == SIG_DFL)
       /* `SIGINT' is handled in the default, fatal manner. */
     else if (query_action.sa_handler == SIG_IGN)
       /* `SIGINT' is ignored. */
     else
       /* A programmer-defined signal handler is in effect. */