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  Constant:  SIG_ACK, SIG_DFL, SIG_ERR, SIG_IGN
 
  Include:   <signal.h>
 
  Synopsis:  The action taken when the interrupt signal is received
             depends on the value of <func>.
 
     The <func> argument must be either a function address or one of
     the manifest constants listed below and defined in SIGNAL.H.
 
     Constant     Meaning
 
     SIG_ACK      Acknowledges receipt of a signal──OS/2 only. This
                  constant is valid only if a user-defined signal
                  handler is installed. Once a process receives a given
                  signal, the operating system does not send any more
                  signals of this type until it receives a SIG_ACK
                  acknowledgement back from the process. The operating
                  system does not queue up signals of a given type;
                  therefore, if more than one signal of a given type
                  accumulates before the process sends back a SIG_ACK
                  value, only the most recent signal is sent to the
                  process after the SIG_ACK value is received by the
                  operating system. This option has no effect on which
                  handler is installed for a given signal. The manifest
                  constant SIG_ACK is not supported for SIGFPE signals.
 
     SIG_DFL      Uses system-default response. Under DOS versions 3.x
                  or earlier, the calling process is terminated and
                  control returns to the DOS command level. If the
                  calling program uses stream I/O, buffers created by
                  the run-time library are not flushed. (DOS buffers
                  are flushed.)
 
                  Under OS/2, the system-default response for all
                  signals is to abort the calling program, with the
                  exception of SIGUSR1, SIGUSR2, and SIGUSR3, whose
                  default is to ignore the signal.
 
     SIG_ERR      Ignores interrupt signal──OS/2 only. This constant
                  is equivalent to SIG_IGN, except that any process
                  trying to send this signal receives an error. A
                  process can use the raise function to send a signal
                  to itself. A different process can send a signal by
                  means of the function DOSFLAGPROCESS (if the signal
                  is SIGUSR1, SIGUSR2, or SIGUSR3) or by means of
                  DOSKILLPROCESS (if the signal is SIGTERM).
 
     SIG_IGN      Ignores interrupt signal. This value should never be
                  given for SIGFPE, since the floating-point state of
                  the process is left undefined.