如何在 C/C++ 程序中使用键盘的特殊键，例如 Command、Shift、Alt、Tab 或功能键？

Question

My Problem is the following:

I want to make a program, a simple text-editor, which can work with all keys of a keyboards set such as the Function Keys (F1 to F12), Command, Left-Shift, ALT or TAB.

More precise, I want to be able to assign all keys to specific operations.

I have made a program to print out the ASCII values of those keys, but the keys doesn´t get accepted as i want to, my test program prints out either values of several ASCII codes or doesn´t accept it all like by pressing the Command Key, instead:

My test-program to print out the ASCII-value of a pressed key:

#include <stdio.h> 

int main (void)
{
    char k;

    printf("\n\n\n\n");

    while(1)
    {

       printf("Please press any key:");

       k = getchar();
       getchar();

       printf("ASCII code of given input key: %d",k);
       printf("\n\n\n");
    }
}

Output after pressing on F2-Key:

Please press any key:^[OQ
ASCII code of given input key: 27


Please press any key:ASCII code of given input key: 81

Output after pressing on F2-Key:

Please press any key:^[[15~
ASCII code of given input key: 27


Please press any key:ASCII code of given input key: 49


Please press any key:ASCII code of given input key: 126

Output after pressing on Command-,Alt- or Left-Shift-Key:

Please press any key:               // no reaction at all

Due to the fact, that i think this must be done easily, because of course its normal to use all keys of a keyboard within a program, it isn´t quite so easy for me as a newbie to find the proper way to achieve that.

I have found that question here on Stackoverflow but it belongs to C#: Special keys on keyboards

Why i can´t fetch an ASCII value of those keys?

Sorry, if i might have an mistaken impression that these keys belong to ASCII values.

Answer 1

Access to "special keys" is not part of the standard library because the language does not assume any specific I/O hardware such as a screen and keyboard, it only assumes standard character based I/O streams, and the data on these streams relate to characters, not keys.

As such receiving keyboard events and scan-codes and platform specific. However there are cross-platform mean by which you can get some commonality across systems that support a keyboard (such as desktop computers - not everything C runs on is a desktop computer).

For example for text console applications such as in your example you might use the ncurses library which is a clone of the Unix curses library, and has a Windows near equivalent in the PDcurses library.

In these curses variants for example, you can write:

int ch = getch() ;
if(ch == KEY_LEFT)
    printw("Left arrow is pressed\n");

Under the hood it is a wrapper for the platform specific means. If cross-platform is not an issue you may utilise these means directly. For example MSVC++ has a conio library, which has a _getch() function similar to that above, except that for non-character keys, it returns 0x00 or 0xE0, and returns teh key code when called a second time.

For GUI applications, the applications message loop will receive keyboard events, the exact means will vary between systems, but again there are cross-platform solutions such as Qt or WxWidgets for example.