IUP Windows ICON

#include <iup.h>
#include <stdlib.h>

//////////////////////////////////////////////////
// Set Windows Icon
#if defined(_WIN32) || defined(WIN32)
#define __windows
#include <windows.h>

WNDPROC orig_proc;
HICON icon;

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) {
    if (msg == WM_SETCURSOR) {
        if (LOWORD(lParam) == HTCLIENT) {
            SetCursor(LoadCursor(NULL, IDC_ARROW));
            return TRUE;
        }
    }
    return CallWindowProc(orig_proc, hwnd, msg, wParam, lParam);
}

void set_win_icon(HWND hwnd) {
    HINSTANCE handle = GetModuleHandle(NULL);
    icon = LoadIcon(handle, "icon");
    SetClassLong(hwnd, GCL_HICON, (LONG) icon);
    orig_proc = (WNDPROC)SetWindowLong(hwnd, GWL_WNDPROC, (LONG) WndProc);
}

void free_win_icon() {
    DestroyIcon(icon);
}
#endif
//////////////////////////////////////////////////

int exit_cb(void) {
    return IUP_CLOSE;
}

int main(int argc, char *argv[]) {
    // declare widgets
    Ihandle *btn, *lbl, *vbox, *dlg;
    // initialize iup
    IupOpen(&argc, &argv);
    // create widgets and set their attributes
    btn = IupButton("&Ok", "");
    IupSetCallback(btn, "ACTION", (Icallback) exit_cb);
    IupSetAttribute(btn, "EXPAND", "Yes");
    IupSetAttribute(btn, "TIP", "Exit button");
    lbl = IupLabel("Hello, world!");
    vbox = IupVbox(lbl, btn, NULL);
    IupSetAttribute(vbox, "GAP", "10");
    IupSetAttribute(vbox, "MARGIN", "10x10");
    IupSetAttribute(vbox, "ALIGNMENT", "ACENTER");
    dlg = IupDialog(vbox);
    IupSetAttribute(dlg, "TITLE", "EXAMPLE");
    //IupSetAttribute(dlg, "ICON", "icon");
    // Map widgets and show dialog
    IupShow(dlg);


    #ifdef __windows
    set_win_icon((HWND)IupGetAttribute(dlg,"HWND"));
    #endif

    // Wait for user interaction
    IupMainLoop();

    #ifdef __windows
    free_win_icon();
    #endif

    // Clean up
    IupDestroy(dlg);
    IupClose();
    return EXIT_SUCCESS;
}