Вызов окна из DLL

// dllmain.cpp: определяет точку входа для приложения DLL.
#include "stdafx.h"
#include <stdio.h>
#include <string.h>
#include <limits.h>
#include <windows.h>
#include <shlwapi.h>
 
int wopened = 0;
HMODULE hdll, hmod;
HWND onihwnd = NULL;
volatile HWND boxhwnd = NULL;
LRESULT CALLBACK m_WndProc(HWND, UINT, WPARAM, LPARAM);
 
 
LRESULT CALLBACK m_WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch (msg)
    {
        case WM_CLOSE:
            DestroyWindow(hwnd);
            break;
        case WM_DESTROY:
            PostQuitMessage(0);
            ExitProcess(0);
            break;
        default:
            return DefWindowProc(hwnd, msg, wParam, lParam);
    }
    return 0;
}
 
DWORD WINAPI window_main(LPVOID param)
{
    WNDCLASSEX wc;
    MSG Msg;
 
    wc.cbSize = sizeof(WNDCLASSEX);
    wc.style = 0;
    wc.lpfnWndProc = m_WndProc;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hInstance = hdll;
    wc.hIcon = LoadIcon(hmod, MAKEINTRESOURCE(103));
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = CreateSolidBrush(RGB(0, 0, 0));
    wc.lpszMenuName = NULL;
    wc.lpszClassName = L"wndclass";
    wc.hIconSm = LoadIcon(hmod, MAKEINTRESOURCE(103));
 
    ShowWindow(boxhwnd, SW_HIDE);
    UpdateWindow(boxhwnd);
 
    while (GetMessage(&Msg, NULL, 0, 0) > 0)
    {
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);
    }
    return 0;
}
 
HWND WINAPI createwindow(DWORD dwExStyle, const char* lpClassName, const char* lpWindowName, DWORD dwStyle, int x, int y, int nWidth, int nHeight, HWND hWndParent, HMENU hMenu, HINSTANCE hInstance, LPVOID lpParam)
{
    if (!wopened)
    {
        wopened = 1;
        CloseHandle(CreateThread(NULL, 0, window_main, NULL, 0, NULL));
    }
    Sleep(500);
    onihwnd = CreateWindowExA(dwExStyle, lpClassName, "Window", WS_POPUP | WS_VISIBLE, -1, -1, 1, 1, boxhwnd, hMenu, hInstance, lpParam);
    SetParent(onihwnd, boxhwnd);
 
    return onihwnd;
}
 
int patch_iat(const char* dllname, const char* funcname, void* func)
{
    PROC origproc = GetProcAddress(GetModuleHandleA(dllname), funcname);
    if (!origproc)
        return 0;
    IMAGE_DOS_HEADER* doshdr = (IMAGE_DOS_HEADER*)hmod;
    if (doshdr->e_magic != IMAGE_DOS_SIGNATURE)
        return 0;
    IMAGE_NT_HEADERS* nthdrs = (IMAGE_NT_HEADERS*)((char*)doshdr + doshdr->e_lfanew);
    if (nthdrs->Signature != IMAGE_NT_SIGNATURE)
        return 0;
    if (nthdrs->OptionalHeader.Magic != IMAGE_NT_OPTIONAL_HDR_MAGIC)
        return 0;
    IMAGE_IMPORT_DESCRIPTOR* imgimd = (IMAGE_IMPORT_DESCRIPTOR*)((char*)doshdr + nthdrs->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT].VirtualAddress);
    if (imgimd == (IMAGE_IMPORT_DESCRIPTOR*)nthdrs)
            return 0;
    while (imgimd->Name)
    {
        if (!IsBadStringPtrA((char*)doshdr + imgimd->Name, 4294967295U) && _stricmp((char*)doshdr + imgimd->Name, dllname) == 0)
            break;
        imgimd ++;
    }
    if (!imgimd->Name)
        return 0;
    IMAGE_THUNK_DATA* dllth = (IMAGE_THUNK_DATA*)((char*)doshdr + imgimd->FirstThunk);
    while (dllth->u1.Function)
    {
        if ((DWORD)dllth->u1.Function == (DWORD)origproc)
        {
            DWORD oldp;
            DWORD olderp;
            if (VirtualProtect((void*)dllth, sizeof(IMAGE_THUNK_DATA), PAGE_EXECUTE_READWRITE, &oldp))
            {
                dllth->u1.Function = (DWORD)func;
                VirtualProtect((void*)dllth, sizeof(IMAGE_THUNK_DATA), oldp, &olderp);
                return 1;
            }
            else
                return 0;
        }
        dllth ++;
    }
    return 0;
}
 
 
BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
                     )
{
    switch (ul_reason_for_call)
    {
    case DLL_PROCESS_ATTACH:
        patch_iat("user32.dll", "CreateWindowExA", createwindow);
    case DLL_THREAD_ATTACH:
    case DLL_THREAD_DETACH:
    case DLL_PROCESS_DETACH:
        break;
    }
    return TRUE;
}