Catch Ctrl-C in C

Question

How does one catch Ctrl C in C

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Set up a trap  you can trap several signals with one handler     signal  SIGQUIT  my handler   signal  SIGINT  my handler     Handle the signal however you want  but be aware of limitations and gotchas    void my handler  int sig         Your code here

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Addendum regarding UN X platforms   According to the signal 2  man page on GNU Linux  the behavior of signal is not as portable as behavior of sigaction      The behavior of signal   varies across UNIX versions  and has also   varied historically across different versions of Linux  Avoid  its   use  use sigaction 2  instead    On System V  system did not block delivery of further instances of the signal and delivery of a signal would reset the handler to the default one  In BSD the semantics changed    The following variation of previous answer by Dirk Eddelbuettel uses sigaction instead of signal    include  lt signal h gt   include  lt stdlib h gt   static bool keepRunning   true   void intHandler int        keepRunning   false     int main int argc  char  argv          struct sigaction act      act sa handler   intHandler      sigaction SIGINT   amp act  NULL        while  keepRunning               main loop

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Peter Varo updated Dirk s answer  but Dirk rejected the change  Here s the new answer by Peter   Although the above snippet is a correct c89 example  one should use the more modern types and guarantees provided by the later standards if possible  Therefore  here is a safer and modern alternative for those who are seeking for the c99 and c11 conforming implementation    include  lt signal h gt   include  lt stdlib h gt   include  lt stdio h gt   static volatile sig atomic t keep running   1   static void sig handler int           void        keep running   0     int main void        signal SIGINT  sig handler        while  keep running          puts  Still running            puts  Stopped by signal  SIGINT         return EXIT SUCCESS         C11 Standard  7 14  2 The header  lt signal h gt  declare a type     sig atomic t which is the  possibly volatile-qualified  integer type of an object that can be accessed as an atomic entity  even in the presence of asynchronous interrupts    Furthermore      C11 Standard  7 14 1 1  5 If the signal occurs other than as the result of calling the abort or raise function  the behavior is undefined if the signal handler refers to any object with static or thread storage duration that is not a lock-free atomic object other than by assigning a value to an object declared as volatile sig atomic t

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Or you can put the terminal in raw mode  like this   struct termios term   term c iflag    IGNBRK  term c iflag  amp     INLCR   ICRNL   IXON   IXOFF   term c lflag  amp     ICANON   ECHO   ECHOK   ECHOE   ECHONL   ISIG   IEXTEN   term c cc VMIN    1  term c cc VTIME    0  tcsetattr fileno stdin   TCSANOW   amp term     Now it should be possible to read Ctrl C keystrokes using fgetc stdin   Beware using this though because you can t Ctrl Z  Ctrl Q  Ctrl S  etc  like normally any more either

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include lt stdio h gt   include lt signal h gt   include lt unistd h gt   void sig handler int signo      if  signo    SIGINT      printf  received SIGINT n       int main void      if  signal SIGINT  sig handler     SIG ERR    printf   ncan t catch SIGINT n         A long long wait so that we can easily issue a signal to this process   while 1       sleep 1     return 0      The function sig handler checks if the value of the argument passed is equal to the SIGINT  then the printf is executed

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This just print before exit    include  lt stdio h gt   include  lt stdlib h gt   include  lt unistd h gt   void sigint handler int    int  main void        signal SIGINT  sigint handler         while  1            pause                           return 0      void sigint handler int sig          do something       printf  killing process  d n  getpid         exit 0

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With a signal handler    Here is a simple example flipping a bool used in main      include  lt signal h gt   static volatile int keepRunning   1   void intHandler int dummy        keepRunning   0             int main void        signal SIGINT  intHandler       while  keepRunning                    Edit in June 2017  To whom it may concern  particularly those with an insatiable urge to edit this answer  Look  I wrote this answer seven years ago  Yes  language standards change   If you really must better the world  please add your new answer but leave mine as is   As the answer has my name on it  I d prefer it to contain my words too  Thank you

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Check here    http   www csl mtu edu cs4411 ck www NOTES signal install html   Note  Obviously  this is a simple example explaining just how to set up a CtrlC handler  but as always there are rules that need to be obeyed in order not to break something else  Please read the comments below   The sample code from above    include   lt stdio h gt   include   lt signal h gt   include   lt stdlib h gt   void     INThandler int    int  main void         signal SIGINT  INThandler        while  1            pause         return 0     void  INThandler int sig         char  c        signal sig  SIG IGN        printf  OUCH  did you hit Ctrl-C  n               Do you really want to quit   y n           c   getchar         if  c     y     c     Y             exit 0        else           signal SIGINT  INThandler        getchar       Get new line character

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Regarding existing answers  note that signal handling is platform dependent   Win32 for example handles far fewer signals than POSIX operating systems  see here   While SIGINT is declared in signals h on Win32  see the note in the documentation that explains that it will not do what you might expect

[c] Catch Ctrl-C in C

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