signal

signal

Define Program Signal Handling

Portability: ISO/ANSI C conforming, UNIX compatible

SYNOPSIS
DESCRIPTION
RETURN VALUE
CAUTION
PORTABILITY
EXAMPLE
RELATED FUNCTIONS
SEE ALSO

SYNOPSIS

#include <signal.h>

   /* This typedef is in <signal.h>. */
typedef void (*_HANDLER)(int);

_HANDLER signal(int signum, _HANDLER handler);

DESCRIPTION

signal defines the action taken when a signal is received by the program. The signum argument is the number of the signal, which should be specified as a symbolic signal name. Refer to the signal names listed in Supported Signals.

The handler argument is the address of the function to be called when the signal occurs. The handler argument can point to a user function, or it can specify one of the two symbolic values SIG_DFL or SIG_IGN. If you specify SIG_IGN, the signal is ignored, if possible; if you specify SIG_DFL, the default action for the signal is taken. (Note that for most signals, the default action is program termination.) Details of what occurs when you specify SIG_DFL or SIG_IGN are provided in the descriptions of the signals. In addition, Tables 5.2 and 5.3 summarize default actions and the results of ignoring signals.

Refer to Handling Signals for a detailed description of how to use signal .

RETURN VALUE

signal returns the address of the previous handler for the signal. If the signal was previously ignored, SIG_IGN is returned; if no action was defined for the signal, SIG_DFL is returned. If the call to signal cannot be honored (for example, if you specify SIG_IGN for a signal that cannot be ignored), the special value SIG_ERR is returned.

CAUTION

When the library discovers a signal with a handler defined by signal , it first restores default signal handling with the following call before it executes the handler you have defined:

signal(signum, SIG_DFL);

Therefore, it is necessary to reissue signal to handle a recurrence of the same signal.

PORTABILITY

The details of signal handling vary widely from system to system. See Using Signals Portably for information on the portable use of signals.

EXAMPLE

#include <lcsignal.h>
#include <float.h>

signal(SIGFPOFL, &overflow_handler);

   /* Perform calculation. */
.
.
.
   /* This function handles a floating-point overflow */
   /* by replacing the result of the computation with */
   /* plus or minus DBL_MAX and allowing the          */
   /* computation to continue.                        */
   /* This example assumes that SIGFPE is not an      */
   /* OpenEdition-managed signal.                     */

void overflow_handler(int signum)
{
   FPE_t *info;
   info = siginfo(); /* Get information about signal. */
   if (!info)

         /* If no information is available, force     */
         /*  default handling.                        */
      raise(SIGFPOFL);

      /* Replace result by appropriate large number.  */
   if (*info->result.doublev < 0.0)
      *info->result.doublev = -DBL_MAX;

   else
      *info->result.doublev = DBL_MAX;
}

RELATED FUNCTIONS

sigaction , cosignal