How to specify kbd modifiers with SendInput()?

Question

I'm using the Windows API SendInput() call to simulate keyboard events. The following snippet (irrelevant details omitted) works perfectly for sending a sequence of characters:

wchar_t txt = ...; INPUT *input = ...; size_t nInput = 0; for (unsigned int j = 0; j < length; j++) { input[nInput].ki.wVk = 0; input[nInput].ki.wScan = txt[j]; input[nInput].ki.dwFlags = KEYEVENTF_UNICODE; nInput++; input[nInput].ki.wVk = 0; input[nInput].ki.wScan = txt[j]; input[nInput].ki.dwFlags = KEYEVENTF_UNICODE | KEYEVENTF_KEYUP; nInput++; } SendInput(nInput, input, sizeoF(INPUT));

Now I'm trying to send single keypresses, with modifiers. I tried the following code:

bool control, alt shift; wchar_t chr; if (control) { input[nInput].ki.wVk = VK_CONTROL; input[nInput].ki.dwFlags = 0; nInput++; } if (alt) { input[nInput].ki.wVk = VK_MENU; input[nInput].ki.dwFlags = 0; nInput++; } if (shift) { input[nInput].ki.wVk = VK_SHIFT; input[nInput].ki.dwFlags = 0; nInput++; } input[nInput].ki.wVk = 0; input[nInput].ki.wScan = chr; input[nInput].ki.dwFlags = KEYEVENTF_UNICODE; nInput++; input[nInput].ki.wVk = 0; input[nInput].ki.wScan = chr; input[nInput].ki.dwFlags = KEYEVENTF_UNICODE | KEYEVENTF_KEYUP; nInput++; if (shift) { input[nInput].ki.wVk = VK_SHIFT; input[nInput].ki.dwFlags = KEYEVENTF_KEYUP; nInput++; } if (alt) { input[nInput].ki.wVk = VK_MENU; input[nInput].ki.dwFlags = KEYEVENTF_KEYUP; nInput++; } if (control) { input[nInput].ki.wVk = VK_CONTROL; input[nInput].ki.dwFlags = KEYEVENTF_KEYUP; nInput++; } SendInput(nInput, input, sizeof(INPUT));

However, modifiers don't seem to get through, i.e., even though, say control is set to true, the event sequence is received as a plain keypress.

Community · Accepted Answer · 2017-05-23 11:43:39Z

Pax's answer did not work out, but it lead me to the correct solution. In short: do not use KEYEVENTF_UNICODE for individual keypresses, rather, convert the character to a virtual key code, and send it that way. Here's the relevant code:

SHORT virtKey = VkKeyScan((TCHAR) chr); input[nInput].ki.wVk = LOBYTE(virtKey); input[nInput].ki.dwFlags = 0; nInput++; input[nInput].ki.wVk = LOBYTE(virtKey); input[nInput].ki.dwFlags = KEYEVENTF_KEYUP; nInput++;

I have not tested how this works for non-ASCII unicode characters, that are mapped to non-English keyboard layouts, and what happens when the layout set for my app is different from the layout set for the application in the front.

@David, you should probably accept this answer otherwise SO will continue to bother you with "have you thought of accepting an answer to this question".
@Pax: sure, I'll do that, but first I wanted to give others a chance to improve my answer or to point out my mistakes.

paxdiablo · Accepted Answer · 2009-03-19 12:20:51Z

The only piece of code I've found which may indicate your problem sets the scan code in the ki structure as well.

Try changing your modifier sections to be:

if (control) { input[nInput].ki.wVk = VK_CONTROL; input[nInput].ki.dwFlags = 0; input[nInput].ki.wScan = MapVirtualKey(VK_CONTROL, 0); nInput++; } if (alt) { input[nInput].ki.wVk = VK_MENU; input[nInput].ki.dwFlags = 0; input[nInput].ki.wScan = MapVirtualKey(VK_MENU, 0); nInput++; } if (shift) { input[nInput].ki.wVk = VK_SHIFT; input[nInput].ki.dwFlags = 0; input[nInput].ki.wScan = MapVirtualKey(VK_SHIFT, 0); nInput++; }

and see if that helps.

If that still doesn't work, try setting the dwFlags to KEYEVENTF_SCANCODE instead of 0 (only for the modifier keys).

Also do it for the key-up events as well and I'm assuming that you're setting input[nInput].type to INPUT_KEYBOARD, yes? Your code doesn't indicate this.

For reference, it was found on this page.

"you're setting input[nInput].type to INPUT_KEYBOARD" - yes, of course.
Not "of course", I never assume anything that's not plainly stated (and sometimes I even doubt those :-). Anyhow, did you try the scan codes?
Fair enough :-) Anyway, the scan codes did not help, but the page you referenced lead me to the solution. I'll post it as an answer. +1, and thanks!
No probs, glad I could help, if only a little. I'm off to bed, it's late here in Oz.

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