signal

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cppreference.com > Other Standard C Functions > signal

signal

Syntax:

  #include <csignal>
  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 the csignal header file):

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.

Example code:

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;
}