signal

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signal

Syntax:

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

The signal() function sets func to be called when signal is recieved by your program. func can be a custom signal handler, or one of these macros (defined in signal.h):

Macro	Explanation
SIG_DFL	default signal handling
SIG_IGN	ignore the signal

Some basic signals that you can attach a signal handler to are:

Signal	Description
SIGTERM	Generic stop signal that can be caught.
SIGINT	Interrupt program, normally ctrl-c.
SIGQUIT	Interrupt program, similar to SIGINT.
SIGKILL	Stops the program. Cannot be caught.
SIGHUP	Reports a disconnected terminal.

The return value of signal() is the address of the previously defined function for this signal, or SIG_ERR is there is an error.

The following example uses the signal() function to call an arbitrary number of functions when the user aborts the program. The functions are stored in a vector, and a single "clean-up" function calls each function in that vector of functions when the program is aborted:

void f1() {
  cout << "calling f1()..." << endl;
}               

void f2() {
  cout << "calling f2()..." << endl;
}               

typedef void(*endFunc)(void);
vector<endFunc> endFuncs;         

void cleanUp( int dummy ) {
  for( unsigned int i = 0; i < endFuncs.size(); i++ ) {
    endFunc f = endFuncs.at(i);
    (*f)();
  }
  exit(-1);
}               

int main() {            

  // connect various signals to our clean-up function
  signal( SIGTERM, cleanUp );
  signal( SIGINT, cleanUp );
  signal( SIGQUIT, cleanUp );
  signal( SIGHUP, cleanUp );            

  // add two specific clean-up functions to a list of functions
  endFuncs.push_back( f1 );
  endFuncs.push_back( f2 );             

  // loop until the user breaks
  while( 1 );           

  return 0;
}