CTRL+C and CTRL+BREAK Signals

The CTRL+C and CTRL+BREAK key combinations receive special handling by console processes. By default, when a console window has the keyboard focus, CTRL+C or CTRL+BREAK is treated as a signal (SIGINT or SIGBREAK) and not as keyboard input. By default, these signals are passed to all console processes that are attached to the console. (Detached processes are not affected.) The system creates a new thread in each client process to handle the event. The thread raises an exception if the process is being debugged. The debugger can handle the exception or continue with the exception unhandled.

CTRL+BREAK is always treated as a signal, but an application can change the default CTRL+C behavior in two ways that prevent the handler functions from being called:

  • The SetConsoleMode function can disable the ENABLE_PROCESSED_INPUT input mode for a console's input buffer, so CTRL+C is reported as keyboard input rather than as a signal.
  • When SetConsoleCtrlHandler is called with NULL and TRUE values for its parameters, the calling process ignores CTRL+C signals. Normal CTRL+C processing is restored by calling SetConsoleCtrlHandler with NULL and FALSE values. This attribute of ignoring or not ignoring CTRL+C signals is inherited by child processes, but it can be enabled or disabled by any process without affecting existing processes.

 

 

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