Registering a Control Handler Function

This is an example of the SetConsoleCtrlHandler function that is used to install a control handler.

When a CTRL+C signal is received, the control handler returns TRUE, indicating that it has handled the signal. Doing this prevents other control handlers from being called.

When a CTRL_CLOSE_EVENT signal is received, the control handler returns TRUE and the process terminates.

When a CTRL_BREAK_EVENT, CTRL_LOGOFF_EVENT, or CTRL_SHUTDOWN_EVENT signal is received, the control handler returns FALSE. Doing this causes the signal to be passed to the next control handler function. If no other control handlers have been registered or none of the registered handlers returns TRUE, the default handler will be used, resulting in the process being terminated.


#include <windows.h> 
#include <stdio.h> 
 
BOOL CtrlHandler( DWORD fdwCtrlType ) 
{ 
  switch( fdwCtrlType ) 
  { 
    // Handle the CTRL-C signal. 
    case CTRL_C_EVENT: 
      printf( "Ctrl-C event\n\n" );
      Beep( 750, 300 ); 
      return( TRUE );
 
    // CTRL-CLOSE: confirm that the user wants to exit. 
    case CTRL_CLOSE_EVENT: 
      Beep( 600, 200 ); 
      printf( "Ctrl-Close event\n\n" );
      return( TRUE ); 
 
    // Pass other signals to the next handler. 
    case CTRL_BREAK_EVENT: 
      Beep( 900, 200 ); 
      printf( "Ctrl-Break event\n\n" );
      return FALSE; 
 
    case CTRL_LOGOFF_EVENT: 
      Beep( 1000, 200 ); 
      printf( "Ctrl-Logoff event\n\n" );
      return FALSE; 
 
    case CTRL_SHUTDOWN_EVENT: 
      Beep( 750, 500 ); 
      printf( "Ctrl-Shutdown event\n\n" );
      return FALSE; 
 
    default: 
      return FALSE; 
  } 
} 
 
int main( void ) 
{ 
  if( SetConsoleCtrlHandler( (PHANDLER_ROUTINE) CtrlHandler, TRUE ) ) 
  { 
    printf( "\nThe Control Handler is installed.\n" ); 
    printf( "\n -- Now try pressing Ctrl+C or Ctrl+Break, or" ); 
    printf( "\n    try logging off or closing the console...\n" ); 
    printf( "\n(...waiting in a loop for events...)\n\n" ); 
 
    while( 1 ){ } 
  } 
  else 
  {
    printf( "\nERROR: Could not set control handler"); 
    return 1;
  }
return 0;
}


 

 

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