Why does the Sleep() function prevent the entire loop from working? - c

Question

The goal is to create a program that logs keystrokes and writes it into a text file. Currently, just tapping a key will write that key a hundred times so I'm trying to slow it down a bit.
However, using Sleep() will prevent this whole code from doing anything at all unless I use Sleep(0) (which, as I understand, means "Do not let lower priority threads run").
Code:
// Subconsole is Windows so the running app is not visible to a certain someone
int __stdcall WinMain(_In_ HINSTANCE hinstance, _In_opt_ HINSTANCE hprevinstance, _In_ LPSTR lpcmdline, _In_ int ncmdshow)
{
FILE* write;
char running = 1;
fopen_s(&write, "typelog.txt", "w");
while (running)
{
_Bool keytoggle;
char key;
// Go from A to Z and see if the key for that was pressed
for (int i = 0x41; i < 0x5A; i++)
{
// Is the highest order bit for GetAsyncKeyState a 1 (is the key down)
keytoggle = (GetAsyncKeyState(i) & (1 << 15)) != 0;
if (keytoggle)
{
key = i; // save the key that was pressed
break;
}
}
// If the key was pressed, write it, otherwise write a space
if (keytoggle)
{
if (write)
fprintf(write, "%c", key);
}
else
{
if (write)
fprintf(write, " ");
}
// Sleep for like, just one millisecond please
Sleep(1);
}
return 0;
}
I have heard that using Sleep, even for a 1ms, can be extended to 20ms because of the system timer. Is that the case? Even if it was, why would the code not be executed at all?
I've searched for an hour or so and found nothing. If you can help it'd be great.

Answer 1

With debugging, the problem is your txt handle is not closed when calling Sleep(1). You can use Message-Only Windows and Raw Input to achieve your goal. For example:
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
hInst = hInstance; // Store instance handle in our global variable
HWND hWnd = CreateWindow(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, HWND_MESSAGE, nullptr, hInstance, nullptr);
if (!hWnd)
{
return FALSE;
}
ShowWindow(hWnd, nCmdShow);
UpdateWindow(hWnd);
RawInput(hWnd);
return TRUE;
}
and
#define BUFFER 512
HRESULT ShowRawInputInfo(LPARAM lParam)
{
UINT dwSize = 0;
HRESULT hResult;
GetRawInputData((HRAWINPUT)lParam, RID_INPUT, NULL, &dwSize, sizeof(RAWINPUTHEADER));
LPBYTE lpb = new BYTE[dwSize];
if (lpb == NULL)
{
return 0;
}
if (GetRawInputData((HRAWINPUT)lParam, RID_INPUT, lpb, &dwSize, sizeof(RAWINPUTHEADER)) != dwSize)
OutputDebugString(TEXT("GetRawInputData does not return correct size !\n"));
RAWINPUT* raw = (RAWINPUT*)lpb;
WCHAR szTempOutput[BUFFER];
if (raw->header.dwType == RIM_TYPEKEYBOARD)
{
hResult = StringCchPrintf(szTempOutput, BUFFER,
TEXT(" Kbd: make=%04x Flags:%04x Reserved:%04x ExtraInformation:%08x, msg=%04x VK=%04x \n"),
raw->data.keyboard.MakeCode,
raw->data.keyboard.Flags,
raw->data.keyboard.Reserved,
raw->data.keyboard.ExtraInformation,
raw->data.keyboard.Message,
raw->data.keyboard.VKey);
if (FAILED(hResult))
{
// TODO: write error handler
}
OutputDebugString(szTempOutput);
}
else if (raw->header.dwType == RIM_TYPEMOUSE)
{
hResult = StringCchPrintf(szTempOutput, BUFFER,
TEXT("Mouse: usFlags=%04x ulButtons=%04x usButtonFlags=%04x usButtonData=%04x ulRawButtons=%04x lLastX=%04x lLastY=%04x ulExtraInformation=%04x\r\n"),
raw->data.mouse.usFlags,
raw->data.mouse.ulButtons,
raw->data.mouse.usButtonFlags,
raw->data.mouse.usButtonData,
raw->data.mouse.ulRawButtons,
raw->data.mouse.lLastX,
raw->data.mouse.lLastY,
raw->data.mouse.ulExtraInformation);
if (FAILED(hResult))
{
// TODO: write error handler
}
OutputDebugString(szTempOutput);
}
delete[] lpb;
return 0;
}
//
// FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
// PURPOSE: Processes messages for the main window.
//
// WM_COMMAND - process the application menu
// WM_PAINT - Paint the main window
// WM_DESTROY - post a quit message and return
//
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
DWORD dwStyleOfStaticText = 0;
HWND hBmp2 = NULL;
WORD reason = 0;
switch (message)
{
case WM_INPUT:
{
ShowRawInputInfo(lParam);
break;
}
case WM_KEYDOWN:
WCHAR szTempOutput[512];
StringCchPrintf(szTempOutput, 512,
TEXT(" KeyValue=%04x\n"), wParam);
OutputDebugString(szTempOutput);
//PostMessage(hWnd, WM_COMMAND, KILLTHEWIN, 0);// hope it serializes message
//PostQuitMessage(0);
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}
Edit: Or Hook