c++ - Sending Two or more chars using SendInput

Question

To send a char, we can use SendInput. How can I use it to send more than one char?

I tried this code but it does not send anything:

INPUT in;
in.type=INPUT_KEYBOARD;
in.ki.wScan=0;
in.ki.time=0;
in.ki.dwExtraInfo=0;
in.ki.wVk=0x53+0x54;

SendInput(2,&in,sizeof(INPUT));

So, what is the right way?

Answer 1

The first parameter of SendInput() specifies how many INPUT structures you are passing in. You are only passing in 1, but you are telling SendInput() that you are passing in 2.

You cannot specify two separate virtual keys in a single INPUT. You need to declare an array of multiple INPUTs, one for each virtual key, and don't forget to include 2 INPUTs for each virtual key - one for the keydown event and one for the keyup event. So, in your example, you actually need 4 INPUTs to send 2 virtual keys, as shown in @user4581301's answer.

Now, regarding KEYEVENTF_UNICODE, you don't use virtual keys with it, you use actual Unicode codepoints instead, where they are specified using UTF-16 codeunits, one per INPUT. So that means if you want to send a Unicode codepoint that requires a UTF-16 surrogate pair, you need 2 INPUTs, one for the high surrogate and one for the low surrogate. That caveat is NOT mentioned in the SendInput() documentation, but it is implied by the fact that the vScan field is a 16bit WORD, and that KEYEVENTF_UNICODE events generate WM_CHAR messages, which passes UTF-16 surrogate codeunits as separate messages.

So, to send a string of Unicode characters using KEYEVENTF_UNICODE, you can do something like this:

#include <vector>
#include <string>

void SendInputString(const std::wstring &str)
{
    int len = str.length();
    if (len == 0) return;

    std::vector<INPUT> in(len*2);
    ZeroMemory(&in[0], in.size()*sizeof(INPUT));

    int i = 0, idx = 0;
    while (i < len)
    {
        WORD ch = (WORD) str[i++];

        if ((ch < 0xD800) || (ch > 0xDFFF))
        {
            in[idx].type = INPUT_KEYBOARD;
            in[idx].ki.wScan = ch;
            in[idx].ki.dwFlags = KEYEVENTF_UNICODE;
            ++idx;

            in[idx] = in[idx-1];
            in[idx].ki.dwFlags |= KEYEVENTF_KEYUP;
            ++idx;
        }
        else
        {
            in[idx].type = INPUT_KEYBOARD;
            in[idx].ki.wScan = ch;
            in[idx].ki.dwFlags = KEYEVENTF_UNICODE;
            ++idx;

            in[idx].type = INPUT_KEYBOARD;
            in[idx].ki.wScan = (WORD) str[i++];
            in[idx].ki.dwFlags = KEYEVENTF_UNICODE;
            ++idx;

            in[idx] = in[idx-2];
            in[idx].ki.dwFlags |= KEYEVENTF_KEYUP;
            ++idx;

            in[idx] = in[idx-2];
            in[idx].ki.dwFlags |= KEYEVENTF_KEYUP;
            ++idx;
        }
    }

    SendInput(in.size(), &in[0], sizeof(INPUT));
}