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POToAscii/ToUnicode in a keyboard hook destroys dead keys
 

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  1. POToAscii/ToUnicode in a keyboard hook destroys dead keys
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    <p>It seems that if you call <code>ToAscii()</code> or <code>ToUnicode()</code> while in a global WH_KEYBOARD_LL hook, and a dead-key is pressed, it will be 'destroyed'.</p> <p>For example, say you've configured your input language in Windows as Spanish, and you want to type an accented letter <b>á</b> in a program. Normally, you'd press the single-quote key (the dead key), then the letter "a", and then on the screen an accented <b>á</b> would be displayed, as expected.</p> <p>But this doesn't work if you call <code>ToAscii()</code> or <code>ToUnicode()</code> in a low-level keyboard hook function. It seems that the dead key is destroyed, and so no accented letter <b>á</b> shows up on screen. Removing a call to the above functions resolves the issue... but unfortunately, I need to be able to call those functions.</p> <p>I Googled for a while, and while a lot of people seemed to have this issue, no good solution was provided.</p> <p>Any help would be much appreciated!</p> <p><b>EDIT:</b> I'm calling <code>ToAscii()</code> to convert the virtual-key code and scan code received in my <a href="http://msdn.microsoft.com/en-us/library/ms644985%28VS.85%29.aspx" rel="noreferrer">LowLevelKeyboardProc</a> hook function into the resulting character that will be displayed on screen for the user.</p> <p>I tried <code>MapVirtualKey(kbHookData->vkCode, 2)</code>, but this isn't as "complete" a function as <code>ToAscii()</code>; for example, if you press Shift + 2, you'll get '2', not '@' (or whatever Shift + 2 will produce for the user's keyboard layout/language).</p> <p><code>ToAscii()</code> is perfect... until a dead-key is pressed.</p> <p><B>EDIT2:</b> Here's the hook function, with irrelevant info removed:</p> <pre><code>LRESULT CALLBACK keyboard_LL_hook_func(int code, WPARAM wParam, LPARAM lParam) { LPKBDLLHOOKSTRUCT kbHookData = (LPKBDLLHOOKSTRUCT)lParam; BYTE keyboard_state[256]; if (code &lt; 0) { return CallNextHookEx(keyHook, code, wParam, lParam); } WORD wCharacter = 0; GetKeyboardState(&amp;keyboard_state); int ta = ToAscii((UINT)kbHookData-&gt;vkCode, kbHookData-&gt;scanCode, keyboard_state, &amp;wCharacter, 0); /* If ta == -1, a dead-key was pressed. The dead-key will be "destroyed" * and you'll no longer be able to create any accented characters. Remove * the call to ToAscii() above, and you can then create accented characters. */ return CallNextHookEx(keyHook, code, wParam, lParam); } </code></pre>
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    1. COPlease show the code for the call to ToUnicode(). Where do you get the lpKeyState parameter?
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    2. CO@jdigital: Well, I'm personally calling ToAscii, but I've read it happens with ToUnicode, too. My call is basically ToAscii(kbHookData->vkCode, kbHookData->scanCode, GetKeyboardState(), &lpchar, 0) in the WH_KEYBOARD_LL hook function. When the ToAscii call returns -1, this means a dead key was pressed... and the dead key is 'destroyed' as I explained above.
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    3. COI deleted my answer, it was completely incorrect based on the assumption that you were referring to c-runtime functions to convert strings rather than Win32 apis to convert scancodes... sorry.
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