Issue with WinAPI SendInput code

Question

I am writing a program, and it is going well so far, however I have an issue with the following code:

void Send(string content) {
    unsigned int size = content.size();
    INPUT *inputs = new INPUT[size];

    for (unsigned int i = 0; i < size; i++) {
        inputs[i].type = 1;
        inputs[i].ki.wVk          = 0;//LOWORD(VkKeyScan(content.at(i)));
        inputs[i].ki.wScan        = content.at(i);
        inputs[i].ki.dwFlags      = KEYEVENTF_UNICODE | KEYEVENTF_SCANCODE;
        inputs[i].ki.time         = 0;
        inputs[i].ki.dwExtraInfo  = ::GetMessageExtraInfo();
    }

    SendInput(size, inputs, sizeof(*inputs)*size);

    for (unsigned int i = 0; i < size; i++) {
        inputs[i].ki.dwFlags &= KEYEVENTF_KEYUP;
    }

    SendInput(size, inputs, sizeof(*inputs)*size);
}

What I am trying to achieve is being able to send input like this:

Send(string("Hello World!"));

However, it does everything it should not, such as moving the cursor even though the type is set to the keyboard. At most, it outputs one character. As you see on line 2, I have an INPUT array. However, when I view this in the debugger, it appears simply as a single INPUT structure, rather than an array of structures.

I am using g++ with gdb debugger + Code::Blocks IDE.

Thanks guys.

EDIT

NEW CODE:

void Send(string content) {
    unsigned int size = content.size();
    INPUT *inputs = new INPUT[size];
    INPUT curr[1];

    ZeroMemory(inputs, sizeof(*inputs)*size);

    for (unsigned int i = 0; i < size; i++) {
        inputs[i].type = 1;
        inputs[i].ki.wVk          = 0;//LOWORD(VkKeyScan(content.at(i)));
        inputs[i].ki.wScan        = content.at(i);
        inputs[i].ki.dwFlags      = KEYEVENTF_UNICODE | KEYEVENTF_SCANCODE;
        inputs[i].ki.time         = 0;
        inputs[i].ki.dwExtraInfo  = ::GetMessageExtraInfo();
    }

    for (unsigned int i = 0; i < size; i++) {
        curr[0] = inputs[i];            // Current input
        int a = ::SendInput(1, (INPUT*)&curr, sizeof(curr));

        inputs[i].ki.dwFlags &= KEYEVENTF_KEYUP;

        curr[0] = inputs[i];
        int b = ::SendInput(1, (INPUT*)&curr, sizeof(curr));

        TCHAR *buff = new TCHAR[3];

        wsprintf(buff, "%i %i", a, b);

        MessageBox(NULL, buff, "SendInput return vals", 0);
    }
}

This still sends nothing.

Now you've got useless casts. The memory leak is still there. And you're overrunning buff and trashing nearby memory in the process. — Ben Voigt
– Ben Voigt, Commented May 29, 2012 at 14:46

Ben Voigt · Accepted Answer · 2012-05-29 13:15:38Z

2

sizeof(*inputs)*size

This is wrong, the cbSize parameter is the size of one INPUT structure, not the total size of the array.

You would have discovered this if you hadn't thrown away the SendInput return value. checking return values is the most basic troubleshooting possible when things go wrong.

You also have a memory leak. And you should use ZeroMemory on the array before filling it in.

Finally, you're pressing all the keys before releasing any of them. If you want to type text, you should press and release each key in sequence, so that no more than one key is pressed at a time.

answered May 29, 2012 at 13:15

Ben Voigt

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4 Comments

Shane Over a year ago

Ben, cbSize is not the error - I updated the source. However I will remove that. Thanks. ZeroMemory once on the whole array? Or individually on each index? And can you please explain how you know I have this memory leak please? So I need to press one, then release one before continuing?

Shane Over a year ago

Ah, I see. So at the end I just have to delete[] inputs? And those casts to INPUT* were required, as the compiler was erroring.

Ben Voigt Over a year ago

@Shane: ::SendInput(1, curr, sizeof curr); should work, no casts. And yes, delete [] inputs; is correct, although now you've added another allocation.

Shane Over a year ago

curr is not dynamic, so it should not be an issue as far as memory leaks go?

marcinj · Accepted Answer · 2012-05-29 16:30:24Z

1

I suppose it is because you are sending only KEYDOWN messages. You might want to try sending first KEYDOWN, then KEYEVENTF_KEYUP for the same character.

[edit for NEW CODE]

few hints:

remove KEYEVENTF_SCANCODE
string is for char strings, for UNICODE use wstring
before testing your function make sure that some app with editbox is foreground, for example Notepad

edited May 29, 2012 at 16:30

answered May 29, 2012 at 11:57

marcinj

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2 Comments

Shane Over a year ago

luskan, I have now implemented it, however I have had no success. Updated the code. I still believe it is related to the INPUT array.

Shane Over a year ago

I had notepad up :) And thanks so much - it works now! I can't believe it is because I was not using unicode. Have a great day!

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