Even though I changed the WM_SETFOCUS section of the code under the “Processing Keyboard Input” heading in the link below to use a bitmap for caret, I cannot get any caret image on the screen and no error message from CreateCaret() function. I have checked that the code created a bitmap or not.

https://learn.microsoft.com/tr-tr/windows/win32/menurc/using-carets

        case WM_SETFOCUS:
        {
             int caret_width = (nCharX/5)>=2 ? nCharX/5 : 2;
             RECT rcCaret = { 0, 0, caret_width, nCharY };
             hdc = GetDC(hwnd);
             HBITMAP hBitmapNew = CreateCompatibleBitmap(hdc, caret_width, nCharY);
             HDC hdcMemNew = CreateCompatibleDC(hdc);
             SelectObject(hdcMemNew, hBitmapNew);
             HBRUSH caretBrush = CreateSolidBrush(RGB(255,0,0));
             FillRect(hdcMemNew, &rcCaret, caretBrush);

             if(CreateCaret(hwnd, (HBITMAP) hBitmapNew, 0, 0)==0) {
                MessageBox(NULL, "CreateCaret() error!", "Error", MB_OK) ;
             }

             // CreateCaret(hwnd, 0, nCharX, nCharY); // Adjust the caret position.
             SetCaretPos(nCaretPosX * nCharX, nCaretPosY * nCharY); // Display the caret.
             ShowCaret(hwnd);

             DeleteObject(caretBrush);
             DeleteObject(hdcMemNew);
             DeleteObject(hBitmapNew);
             ReleaseDC(hwnd, hdc);
        }
        break;

I tried to change caret bitmap, but no caret image on the window.