signal()

Associates a signal handler with a signal.

  #include <signal.h> 
  void (*signal(int sig, void (*func)(int)))(int);

Parameter

sig

A signal number.

func

A pointer to a signal handling function.

Remarks

The signal() function returns a pointer to a signal handling routine that takes an int value argument.

The sig argument is the signal number associated with the signal handling function. The signals defined in signal.h are listed in the table below.

Table 1. Signal Description
Macro	Signal
`SIGABRT`	Abort signal. Defined as a positive integer value. This signal is called by the `abort()`function.
`SIGBREAK`	Terminates the calling program.
`SIGFPE`	Floating point exception signal. Defined as a positive integer value.
`SIGILL`	Illegal instruction signal. Defined as a positive integer value.
`SIGINT`	Interactive user interrupt signal. Defined as a positive integer value.
`SIGSEGV`	Segment violation signal. Defined as a positive integer value.
`SIGTERM`	Terminal signal. Defined as a positive integer value. When raised this signal terminates the calling program by calling the `exit()`function.

The func argument is the signal handling function. This function is either programmer supplied or one of the pre-defined signal handlers listed in the table below.

Table 2. Signal-handling Functions
Function	Action
`SIG_IGN`	Nothing. It is used as a function argument in `signal()`to designate that a signal be ignored.
`SIG_DFL`	Aborts the program by calling `abort()`.
`SIG_ERR`	Returned by `signal()`when it cannot honor a request passed to it.

When it is raised, a signal handler's execution is preceded by the invocation of signal(sig, SIG_DFL). This call to signal() disables the user's handler. It can be reinstalled by placing a call within the user handler to signal() with the user's handler as its function argument.

This function returns a pointer to the signal handling function set by the last call to signal() for signal sig. If the request cannot be honored, signal() returns SIG_ERR.

This facility may not be available on some configurations of the EWL.

Listing: Example of signal() usage


#include <signal.h> 
#include <stdio.h> 
#include <stdlib.h> 
void userhandler(int); 
void userhandler(int sig) 
{ 
char c; 
printf("userhandler!\nPress return.\n"); 
/* wait for the return key to be pressed */ 
c = getchar(); 
} 
int main(void) 
{ 
void (*handlerptr)(int); 
int i; 
handlerptr = signal(SIGINT, userhandler); 
if (handlerptr == SIG_ERR) 
printf("Can't assign signal handler.\n"); 
for (i = 0; i < 10; i++) { 
printf("%d\n", i); 
if (i == 5) 
raise(SIGINT); 
} 
return 0; 
} 
Output: 
0 
1 
2 
3 
4 
CodeWarrior Implementation of the C Standard Library 153 
5 
userhandler! 
Press return. 
6 
7 
8 
9