Find main window of given process id

find_main_window.c

#include <windows.h>

HWND FindMainWindow(DWORD pid) {
    HANDLE threadSnap = INVALID_HANDLE_VALUE;
    threadSnap = CreateToolhelp32Snapshot(TH32CS_SNAPTHREAD, pid);
    if(threadSnap == INVALID_HANDLE_VALUE) return NULL;

    THREADENTRY32 entry = { sizeof(THREADENTRY32) };

    HWND win = NULL;
    BOOL CALLBACK enumThreadWinCb(HWND hwnd, LPARAM lParam) {
        win = hwnd;
        return FALSE;
    }

    BOOL res;
    for (res = Thread32First(threadSnap, &entry); res; res = Thread32Next(threadSnap, &entry)) {
        if (entry.th32OwnerProcessID != pid) continue;

        EnumThreadWindows(entry.th32ThreadID, enumThreadWinCb, 0);
        if (win) break;
    }

    CloseHandle(threadSnap);

    return win;
}