How do I check if a Key is pressed on C

Question

How could I possibly check if a Key is pressed on Windows

User · Answer

Are you talking about getchar function   http   en cppreference com w c io getchar

User · Answer

check if a key is pressed  if yes  then do stuff   Consider  select     if this  reportedly Posix  function is available on your os    select    uses 3 sets of bits  which you create using functions provided  see man select  FD SET  etc    You probably only need create the input bits  for now     from man page    select     allow a program to monitor multiple file descriptors  waiting until one or more of the file descriptors become  ready  for some class of I O operation   e g   input  possible   A file descriptor is considered ready if it is possible to perform a corresponding I O operation  e g   read 2   without  blocking       When select is invoked   a  the function looks at each fd identified in the sets  and if that fd state indicates you can do something  perhaps read  perhaps write   select will return and let you go do that      all you got to do  is scan the bits  find the set bit  and take action on the fd associated with that bit     The 1st set  passed into select  contains active input fd s  typically devices   Probably 1 bit in this set is all you will need   And with only 1 fd  i e  an input from keyboard   1 bit  this is all quite simple   With this return from select  you can  do-stuff   perhaps  after you have fetched the char    b  the function also has a timeout  with which you identify how much time to await a change of the fd state  If the fd state does not change  the timeout will cause  select    to return with a 0   i e  no keyboard input  Your code can do something at this time  too  perhaps an output   fyi - fd s are typically 0 1 2    Remembe that C uses 0 as STDIN  1 and STDOUT     Simple test set up  I open a terminal  separate from my console   and type the tty command in that terminal to find its id   The response is typically something like   dev pts 0   or 3  or 17      Then I get an fd to use in  select    by using open      flag options are  O RDONLY  O WRONLY  or O RDWR int inFD   open    dev pts 5   O RDONLY       It is useful to cout this value    Here is a snippet to consider  from man select      fd set rfds    struct timeval tv    int retval        Watch stdin  fd 0  to see when it has input       FD ZERO  amp rfds     FD SET 0   amp rfds         Wait up to five seconds       tv tv sec   5    tv tv usec   0     retval   select 1   amp rfds  NULL  NULL   amp tv        Don t rely on the value of tv now        if  retval    -1        perror  select        else if  retval        printf  Data is available now  n        i e  doStuff            FD ISSET 0   amp rfds  will be true       else       printf  No data within five seconds  n       i e  key not pressed

User · Answer

As mentioned by others there s no cross platform way to do this  but on Windows you can do it like this   The Code below checks if the key  A  is down   if GetKeyState  A    amp  0x8000  Check if high-order bit is set  1  lt  lt  15              Do stuff     In case of shift or similar you will need to pass one of these  https   msdn microsoft com de-de library windows desktop dd375731 v vs 85  aspx  if GetKeyState VK SHIFT   amp  0x8000           Shift down     The low-order bit indicates if key is toggled   SHORT keyState   GetKeyState VK CAPITAL   caps lock      bool isToggled   keyState  amp  1  bool isDown   keyState  amp  0x8000    Oh and also don t forget to   include  lt Windows h gt

User · Answer

There is no portable function that allows to check if a key is hit and continue if not   This is always system dependent     Solution for linux and other posix compliant systems   Here  for Morgan Mattews s code provide kbhit    functionality in a way compatible with any POSIX compliant system  He uses the trick of desactivating buffering at termios level   Solution for windows   For windows  Microsoft offers  kbhit

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