How to convert ASCII character to CGKeyCode?

Question

I need a function that, given a character, returns the CGKeyCode associated with the position of that character on the current keyboard layout. E.g., given "b", it should return kVK_ANSI_B if using U.S. QWERTY, or 45 if using Dvorak. The Win32 API has the function VkKeyScan() for this purpose; X11 has the function XStringToKeySym(). Is there such a function in the CG API?

I need this in order to pass a parameter to CGEventCreateKeyboardEvent(). I've tried using CGEventKeyboardSetUnicodeString() instead, but that apparently does not support modifier flags (which I need).

I have searched extensively for this but cannot find a decent answer. Currently I am using the following code (found online), which works, but is not exactly elegant (and rather difficult to decipher how to simplify) and I would prefer not to use it in production code:

#include <stdint.h>
#include <stdio.h>
#include <ApplicationServices/ApplicationServices.h>

CGKeyCode keyCodeForCharWithLayout(const char c,
                                   const UCKeyboardLayout *uchrHeader);

CGKeyCode keyCodeForChar(const char c)
{
    CFDataRef currentLayoutData;
    TISInputSourceRef currentKeyboard = TISCopyCurrentKeyboardInputSource();

    if (currentKeyboard == NULL) {
     fputs("Could not find keyboard layout\n", stderr);
     return UINT16_MAX;
    }

    currentLayoutData = TISGetInputSourceProperty(currentKeyboard,
                                                kTISPropertyUnicodeKeyLayoutData);
    CFRelease(currentKeyboard);
    if (currentLayoutData == NULL) {
     fputs("Could not find layout data\n", stderr);
     return UINT16_MAX;
    }

    return keyCodeForCharWithLayout(c,
           (const UCKeyboardLayout *)CFDataGetBytePtr(currentLayoutData));
}

/* Beware! Messy, incomprehensible code ahead!
 * TODO: XXX: FIXME! Please! */
CGKeyCode keyCodeForCharWithLayout(const char c,
                                   const UCKeyboardLayout *uchrHeader)
{
    uint8_t *uchrData = (uint8_t *)uchrHeader;
    UCKeyboardTypeHeader *uchrKeyboardList = uchrHeader->keyboardTypeList;

    /* Loop through the keyboard type list. */
    ItemCount i, j;
    for (i = 0; i < uchrHeader->keyboardTypeCount; ++i) {
     /* Get a pointer to the keyToCharTable structure. */
     UCKeyToCharTableIndex *uchrKeyIX = (UCKeyToCharTableIndex *)
     (uchrData + (uchrKeyboardList[i].keyToCharTableIndexOffset));

     /* Not sure what this is for but it appears to be a safeguard... */
     UCKeyStateRecordsIndex *stateRecordsIndex;
     if (uchrKeyboardList[i].keyStateRecordsIndexOffset != 0) {
      stateRecordsIndex = (UCKeyStateRecordsIndex *)
       (uchrData + (uchrKeyboardList[i].keyStateRecordsIndexOffset));

      if ((stateRecordsIndex->keyStateRecordsIndexFormat) !=
          kUCKeyStateRecordsIndexFormat) {
       stateRecordsIndex = NULL;
      }
     } else {
      stateRecordsIndex = NULL;
     }

     /* Make sure structure is a table that can be searched. */
     if ((uchrKeyIX->keyToCharTableIndexFormat) != kUCKeyToCharTableIndexFormat) {
      continue;
     }

     /* Check the table of each keyboard for character */
     for (j = 0; j < uchrKeyIX->keyToCharTableCount; ++j) {
      UCKeyOutput *keyToCharData =
       (UCKeyOutput *)(uchrData + (uchrKeyIX->keyToCharTableOffsets[j]));

      /* Check THIS table of the keyboard for the character. */
      UInt16 k;
      for (k = 0; k < uchrKeyIX->keyToCharTableSize; ++k) {
       /* Here's the strange safeguard again... */
       if ((keyToCharData[k] & kUCKeyOutputTestForIndexMask) ==
           kUCKeyOutputStateIndexMask) {
        long keyIndex = (keyToCharData[k] & kUCKeyOutputGetIndexMask);
        if (stateRecordsIndex != NULL &&
         keyIndex <= (stateRecordsIndex->keyStateRecordCount)) {
         UCKeyStateRecord *stateRecord = (UCKeyStateRecord *)
                                         (uchrData +
         (stateRecordsIndex->keyStateRecordOffsets[keyIndex]));

         if ((stateRecord->stateZeroCharData) == c) {
          return (CGKeyCode)k;
         }
        } else if (keyToCharData[k] == c) {
         return (CGKeyCode)k;
        }
       } else if (((keyToCharData[k] & kUCKeyOutputTestForIndexMask)
          != kUCKeyOutputSequenceIndexMask) &&
            keyToCharData[k] != 0xFFFE &&
                  keyToCharData[k] != 0xFFFF &&
            keyToCharData[k] == c) {
        return (CGKeyCode)k;
       }
      }
     }
    }

    return UINT16_MAX;
}

Is there a.) (preferably) a standard function I am overlooking, or b.) (almost certainly) a more elegant way write my own?

Answer 1

Use a table. Better to use a pointer to a table, which allows the changing of keyboard & character mappings for different keyboards. Also, when making changes, the changes are related to data and don't effect code, so they are much safer.

Answer 2

This is what I ended up using. Much cleaner.

#include <CoreFoundation/CoreFoundation.h>
#include <Carbon/Carbon.h> /* For kVK_ constants, and TIS functions. */

/* Returns string representation of key, if it is printable.
 * Ownership follows the Create Rule; that is, it is the caller's
 * responsibility to release the returned object. */
CFStringRef createStringForKey(CGKeyCode keyCode)
{
    TISInputSourceRef currentKeyboard = TISCopyCurrentKeyboardInputSource();
    CFDataRef layoutData =
        TISGetInputSourceProperty(currentKeyboard,
                                  kTISPropertyUnicodeKeyLayoutData);
    const UCKeyboardLayout *keyboardLayout =
        (const UCKeyboardLayout *)CFDataGetBytePtr(layoutData);

    UInt32 keysDown = 0;
    UniChar chars[4];
    UniCharCount realLength;

    UCKeyTranslate(keyboardLayout,
                   keyCode,
                   kUCKeyActionDisplay,
                   0,
                   LMGetKbdType(),
                   kUCKeyTranslateNoDeadKeysBit,
                   &keysDown,
                   sizeof(chars) / sizeof(chars[0]),
                   &realLength,
                   chars);
    CFRelease(currentKeyboard);    

    return CFStringCreateWithCharacters(kCFAllocatorDefault, chars, 1);
}

/* Returns key code for given character via the above function, or UINT16_MAX
 * on error. */
CGKeyCode keyCodeForChar(const char c)
{
    static CFMutableDictionaryRef charToCodeDict = NULL;
    CGKeyCode code;
    UniChar character = c;
    CFStringRef charStr = NULL;

    /* Generate table of keycodes and characters. */
    if (charToCodeDict == NULL) {
        size_t i;
        charToCodeDict = CFDictionaryCreateMutable(kCFAllocatorDefault,
                                                   128,
                                                   &kCFCopyStringDictionaryKeyCallBacks,
                                                   NULL);
        if (charToCodeDict == NULL) return UINT16_MAX;

        /* Loop through every keycode (0 - 127) to find its current mapping. */
        for (i = 0; i < 128; ++i) {
            CFStringRef string = createStringForKey((CGKeyCode)i);
            if (string != NULL) {
                CFDictionaryAddValue(charToCodeDict, string, (const void *)i);
                CFRelease(string);
            }
        }
    }

    charStr = CFStringCreateWithCharacters(kCFAllocatorDefault, &character, 1);

    /* Our values may be NULL (0), so we need to use this function. */
    if (!CFDictionaryGetValueIfPresent(charToCodeDict, charStr,
                                       (const void **)&code)) {
        code = UINT16_MAX;
    }

    CFRelease(charStr);
    return code;
}

Answer 3

Hey Michael,

Thanks for taking the time to post this. I have been searching high and low for such a solution. I am trying to compile this in XCode and getting a few errors though.

At the moment I am down to two.

error: 'UINT16_MAX' was not declared in this scope

and....

error: invalid conversion from 'void*' to 'const __CFData*'

for this line

TISGetInputSourceProperty(currentKeyboard, kTISPropertyUnicodeKeyLayoutData);

Not sure what the problem is. Do you have an XCode example, I would love to see it.

Anyway I will try and figure it out.

Thanks again for posting

Cheers

Simon

Answer 4

Hi

I keep getting 65535 returned for any char i pass to the keyCodeForChar function... i assume thats because the code dictionary is NULL.

What would cause this, do you think?

Thanks for posting, i've been looking for solutions to key codes for ages!

Joe