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 ssignal()               Implement Software Signals

 #include   <signal.h>

 int        (*ssignal(sig,action))();
 int        sig;                         Type of signal
 int        (*action)();                 Action function/Constant

    ssignal() is used to establish an action routine for servicing a
    signal.  Software signals are integers in the range of 1 to 15.
    'sig' is a number that identifies the type of signal; 'action' is the
    name of a user-defined action function, or it is a constant: SIG_DFL
    (default action) or SIG_IGN (ignore action) (defined in <signal.h>).
    SIG_IGN means the interrupt signal is ignored.  SIG_DFL terminates
    the calling process and returns control to the MS-DOS command level.
    If the action function has been established for 'sig', then that
    action is reset to SIG_DFL, and the action function is entered with
    'sig'.

       Returns:     The action previously established or SIG_DFL, if the
                    signal number is illegal.

   -------------------------------- Example ---------------------------------

    The following statements set up two software signals and call them.

           #include <signal.h>  /* for gsignal, ssignal and SIG_IGN */

           #define ACTION1 1    /* uses software signal #1 */
           #define ACTION2 6    /* uses software signal #6 */

           int action1a()
               {
                   return(100);
               }

           int action1b()
               {
                   return(150);
               }

           int action2()
               {
                   return(200);
               }

           main()
               {
                   int sigval;

                   ssignal(ACTION1,action1a);
                   sigval = gsignal(ACTION1);     /* sigval = 100 */
                   ssignal(ACTION2,action2);
                   sigval = gsignal(ACTION2);     /* sigval = 200 */
                   ssignal(ACTION1,action1b);
                   sigval = gsignal(ACTION1);     /* sigval = 150 */
                   ssignal(ACTION2,SIG_IGN);
                   sigval = gsignal(ACTION2);     /* sigval = 1 */
               }