Array of INPUT / vector doesn't work with SendInput

Question

So I'm trying to use SendInput in order to send multiple key presses / key releases at the same time. The array and vector have the correct information but for some reason it's just not pressing anything. Why?

I have tried picking one element from the array and vector and using SendInput to press / release the key and it works fine.

#include <iostream>
#include <Windows.h>
#include <vector>

class movement
{
public:
    std::vector<INPUT> inputs;

    void Key(std::vector<INPUT> INPUTkeys)
    {
        INPUT * inputs = new INPUT[INPUTkeys.size()];

        for (int i = 0; i < INPUTkeys.size(); i++)
            inputs[i] = INPUTkeys.at(i);

        SendInput(INPUTkeys.size(), inputs, sizeof(inputs));

        delete[] inputs;
    }

    void prepareInput(INPUT &input, int key, bool down)
    {
        input.type = INPUT_KEYBOARD;
        input.ki.dwExtraInfo = NULL;
        input.ki.time = NULL;
        input.ki.wScan = NULL;
        input.ki.wVk = key;

        if (down)
            input.ki.dwFlags = 0;
        else
            input.ki.dwFlags = KEYEVENTF_KEYUP;
    }
};

movement oMovement;

void main()
{
    while (!GetAsyncKeyState(VK_SPACE))
        Sleep(1);

    std::vector<INPUT> inputs;

    INPUT input;

    oMovement.prepareInput(input, 'U', true);
    inputs.push_back(input);
    oMovement.prepareInput(input, 'S', true);
    inputs.push_back(input);
    oMovement.prepareInput(input, 'X', true);
    inputs.push_back(input);

    oMovement.Key(inputs);
    inputs.clear();

    oMovement.prepareInput(input, 'U', false);
    inputs.push_back(input);
    oMovement.prepareInput(input, 'S', false);
    inputs.push_back(input);
    oMovement.prepareInput(input, 'X', false);
    inputs.push_back(input);

    oMovement.Key(inputs);
    inputs.clear();

    system("pause");
}

You need to do oMovement.prepareInput(input, 'U', true) and to immediately follow with oMovement.prepareInput(input, 'U', false); — manuell
– manuell, Commented Mar 2, 2018 at 9:57
std::vector is guaranteed to store data in a contiguous block of memory, just like an array in C. The entire allocation-copying-deletion cycle is not required. — IInspectable
– IInspectable, Commented Mar 2, 2018 at 10:03
Why didn't you do any error checking? Wouldn't that have told you what was wrong? — David Heffernan
– David Heffernan, Commented Mar 2, 2018 at 10:26
@manuell: "You need to do oMovement.prepareInput(input, 'U', true) and to immediately follow with oMovement.prepareInput(input, 'U', false);" - no, you don't. It is perfectly valid to keep a key "held down" while "pressing" other keys. However, what this code should be doing instead is calling Key() only 1 time with all 6 "down" and "up" inputs, not 2 times, first with 3 "down" inputs and then again with 3 "up" inputs. — Remy Lebeau
– Remy Lebeau, Commented Mar 2, 2018 at 19:05

user7860670 · Accepted Answer · 2018-03-02 10:23:05Z

3

You are passing size of pointer as third parameter to SendInput while it should be size of INPUT struct. You also should check the result (at least in debug mode):

void Key(std::vector<INPUT> & INPUTkeys) // pass by reference to prevent copying
{
   ::UINT const sent_events_count
   {
       SendInput
       (
           static_cast<::UINT>(INPUTkeys.size())
       ,   INPUTkeys.data()
       ,   sizeof ::INTPUT
       )
   };
   assert(INPUTkeys.size() == sent_events_count);
}

edited Mar 2, 2018 at 10:23

answered Mar 2, 2018 at 10:15

user7860670

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