getch and arrow codes

Question

I m writing a programm that s using getch   to scan for arrow keys  My code so far is   switch getch          case 65        key up         break      case 66        key down         break      case 67        key right         break      case 68        key left         break      Problem is that when I press  A    B    C  or  D  the code will also executed  because 65 is the decimal code for  A   etc     Is there a way to check for an arrow key without call others   Thanks

User · Answer

I have written a function using getch to get arrow code. it's a quick'n'dirty solution but the function will return an ASCII code depending on arrow key : UP : -10 DOWN : -11 RIGHT : -12 LEFT : -13

Moreover,with this function, you will be able to differenciate the ESCAPE touch and the arrow keys. But you have to press ESC 2 time to activate the ESC key.

here the code :

char getch_hotkey_upgrade(void)
{
  char ch = 0,ch_test[3] = {0,0,0};

    ch_test[0]=getch();

    if(ch_test[0] == 27)
    {
        ch_test[1]=getch();

        if (ch_test[1]== 91)
        {
            ch_test[2]=getch();

            switch(ch_test[2])
            {
            case 'A':
                //printf("You pressed the up arrow key !!\n");
                //ch = -10;
                ch = -10;
                break;
            case 'B':
                //printf("You pressed the down arrow key !!\n");
                ch = -11;
                break;
            case 'C':
                //printf("You pressed the right arrow key !!\n");
                ch = -12;
                break;
            case 'D':
                //printf("You pressed the left arrow key !!\n");
                ch = -13;
                break;
            }
        }
        else
         ch = ch_test [1];
    }
    else
        ch = ch_test [0];
  return ch;
}

User · Answer

So  after alot of struggle  I miraculously solved this everannoying issue   I was trying to mimic a linux terminal and got stuck at the part where it keeps a command history which can be accessed by pressing up or down arrow keys  I found ncurses lib to be painfuly hard to comprehend and slow to learn   char ch   0  k   0  while 1      ch   getch      if ch    27                      if ch is the escape sequence with num code 27  k turns 1 to signal the next     k   1    if ch    91  amp  amp  k    1           if the previous char was 27  and the current 91  k turns 2 for further use     k   2    if ch    65  amp  amp  k    2           finally  if the last char of the sequence matches  you ve got a key       printf  You pressed the up arrow key    n      if ch    66  amp  amp  k    2                                   printf  You pressed the down arrow key    n      if ch    27  amp  amp  ch    91          if ch isn t either of the two  the key pressed isn t up down so reset k     k   0    printf   c -  d   ch  ch         prints out the char and it s int code   It s kind of bold but it explains alot  Good luck

User · Answer

By pressing one arrow key getch will push three values into the buffer      033       A    B    C  or  D    So the code will be something like this   if  getch        033        if the first value is esc     getch       skip the       switch getch         the real value         case  A                  code for arrow up             break          case  B                  code for arrow down             break          case  C                  code for arrow right             break          case  D                  code for arrow left             break

User · Answer

void input from key board int  amp ri  int  amp ci        char ch    x       if   kbhit                  ch    getch            if  ch    -32                        ch    getch                switch  ch                            case 72    ri--  break                case 80    ri    break                case 77    ci    break                case 75    ci--  break                                     else if  ch      r    gotoRowCol ri    ci -  ci             else if  ch      t    gotoRowCol ri  ci    5             else if  ch    27    system  ipconfig              else if  ch    8   cout  lt  lt       gotoRowCol ri  --ci   if  ci  lt   0 gotoRowCol ri--  ci             else   cout  lt  lt  ch  gotoRowCol ri  ci               gotoRowCol ri  ci

User · Answer

for a solution that uses ncurses with working code and initialization of ncurses see  getchar   returns the same value  27  for up and down arrow keys

User · Answer

The keypad will allow the keyboard of the user s terminal to allow for function keys to be interpreted as a single value  i e  no escape sequence    As stated in the man page      The keypad option enables the keypad of the user s terminal  If   enabled  bf is TRUE   the user can press a function key  such as an   arrow key  and wgetch returns a single value representing the function   key  as in KEY LEFT  If disabled  bf is FALSE   curses does not treat   function keys specially and the program has to interpret the escape   sequences itself  If the keypad in the terminal can be turned on  made   to transmit  and off  made to work locally   turning on this option   causes the terminal keypad to be turned on when wgetch is called  The   default value for keypad is false

User · Answer

getch    function returns two keycodes for arrow keys  and some other special keys   as mentioned in the comment by FatalError  It returns either 0  0x00  or 224  0xE0  first  and then returns a code identifying the key that was pressed   For the arrow keys  it returns 224 first followed by 72  up   80  down   75  left  and 77  right   If the num-pad arrow keys  with NumLock off  are pressed  getch    returns 0 first instead of 224   Please note that getch    is not standardized in any way  and these codes might vary from compiler to compiler  These codes are returned by MinGW and Visual C   on Windows   A handy program to see the action of getch    for various keys is    include  lt stdio h gt   include  lt conio h gt   int main          int ch       while   ch    getch       27     27   Esc key                  printf   d   ch           if  ch    0    ch    224              printf      d    getch               printf   n               printf  ESC  d n   ch        return  0       This works for MinGW and Visual C    These compilers use the name  getch    instead of getch    to indicate that it is a non-standard function   So  you may do something like   ch    getch     if  ch    0    ch    224        switch   getch                   case 72                 Code for up arrow handling                break           case 80                 Code for down arrow handling                break                  etc

User · Answer

how about trying this   void CheckKey void    int key  if  kbhit          key getch        if  key    224            do               key getch              while key  224           switch  key                case 72                  printf  up                    break              case 75                  printf  left                    break              case 77                  printf  right                    break              case 80                  printf  down                    break                      printf   d n  key      int main         while  1            if  kbhit                  CheckKey                         if you can t understand why there is 224  then try running this code      include  lt stdio h gt   include  lt conio h gt   int main         while  1            if  kbhit                  printf   d n  getch                         but I don t know why it s 224  can you write down a comment if you know why

User · Answer

I m Just a starter  but i v created a char for example  b    and I do b    getch     its a conio h library s command  And check  If  b    -32  b    getch      And do check for the keys  72 up  80 down  77 right  75 left

User · Answer

Actually  to read arrow keys one need to read its scan code  Following are the scan code generated by arrow keys press  not key release      When num Lock is off    Left E0 4B  Right E0 4D  Up E0 48  Down E0 50      When Num Lock is on these keys get preceded with E0 2A    Byte E0 is -32 Byte 48 is 72 UP Byte 50 is 80 DOWN  user var getch    if user var    -32        user var getch        switch user var            case 72          cur sel--          if  cur sel  0              cur sel 4          break      case 80          cur sel            if cur sel  5              cur sel 1          break              In the above code I have assumed programmer wants to move 4 lines only

User · Answer

Try this     I am in Windows 7 with Code  Blocks  while  true        char input      input   getch         switch input            case -32    This value is returned by all arrow key  So  we don t want to do something          break      case 72          printf  up            break      case 75          printf  left            break      case 77          printf  right            break      case 80          printf  down            break      default          printf  INVALID INPUT             break

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