Software signals made available to users are associated with integers in the inclusive range 1 through 17. A call to ssignal() associates a procedure, action, with the software signal sig; the software signal, sig, is raised by a call to gsignal(). Raising a software signal causes the action established for that signal to be taken.

The first argument to ssignal() is a number identifying the type of signal for which an action is to be established. The second argument defines the action; it is either the name of a (user-defined) action function or one of the manifest constants SIG_DFL (default) or SIG_IGN (ignore). The ssignal() function returns the action previously established for that signal type; if no action has been established or the signal number is illegal, ssignal() returns SIG_DFL.

The gsignal() raises the signal identified by its argument, sig.

If an action function has been established for sig, then that action is reset to SIG_DFL and the action function is entered with argument sig. The gsignal() function returns the value returned to it by the action function.

If the action for sig is SIG_IGN, gsignal() returns the value 1 and takes no other action.

If the action for sig is SIG_DFL, gsignal() returns the value 0 and takes no other action.

If sig has an illegal value or no action was ever specified for sig, gsignal() returns the value 0 and takes no other action.