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!
This question is related to
c
character
decimal
arrow-keys
getch
void input_from_key_board(int &ri, int &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 << " "; gotoRowCol(ri, --ci); if (ci <= 0)gotoRowCol(ri--, ci); }
else { cout << ch; gotoRowCol(ri, ci++); }
gotoRowCol(ri, ci);
}
}
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;
}
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 <stdio.h>
#include <conio.h>
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 ... */
}
}
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 <stdio.h>
#include <conio.h>
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?
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.
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 && k == 1) // if the previous char was 27, and the current 91, k turns 2 for further use
k = 2;
if(ch == 65 && 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 && k == 2)
printf("You pressed the down arrow key !!\n");
if(ch != 27 && 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 !
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;
}
}
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)
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
When Num Lock is on these keys get preceded with E0 2A
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.
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
Source: Stackoverflow.com