c - How to stop reading from keyboard once a signal is handled? -

i'm writing program sigint signal handled first time sent, set default after that. so, example, have this:

static volatile int stop_terminating = 1;  void handler(int dummy) {     stop_terminating = 0; }  int main(){     signal(sigint, handler);     char input[256];     while(1){         if(stop_terminating == 0){             // reset action of signal default             signal(sigint, sig_dfl);             printf("message sent.\n");             // increment counter doesn't enter condition again             stop_terminating++;         }         printf("user input:\n");         fgets(input, sizeof(input), stdin);         // in stage, wanna press ctrl+c , print message, stopping fgets         // happens is: press ctrl+c, signal catched, fgets         // still asking input, , after send something, message printed         // because looped through while(1) again.     } } 

how can stop fgets asking input , print message , ask again input?

the linux manual page signals says that

interruption of system calls , library functions signal handlers

if signal handler invoked while system call or library function call blocked, either:

• the call automatically restarted after signal handler returns; or

• the call fails error eintr.

which of these 2 behaviors occurs depends on interface , whether or not signal handler established using sa_restart flag (see sigaction(2)).

you may use either siginterrupt() function signal(), or use sigaction() instead of signal() registering signal handler, in order disable restarting read() system call after signal.

note fgets() c library might call read() multiple times until newline character found, therefore may need switch using lower-level functions instead of stdio.h apis.