Question

How to know when EnumWindows finishes its listing of windows? Because EnumWindows receives a callback function as parameter, and it keeps calling it until no more windows to be listed.

Answer 1

EnumWindows() blocks while enumeration is taking place. When EnumWindows() finishes enumerating through the windows, it returns a BOOL.

The following code snippet:

#include <windows.h>
#include <cstdio>

BOOL CALLBACK MyEnumWindowsProc(HWND hwnd, LPARAM lparam)
{
    int& i = *(reinterpret_cast<int*>(lparam));
    ++i;
    char title[256];
    ::GetWindowText(hwnd, title, sizeof(title));
    ::printf("Window #%d (%x): %s\n", i, hwnd, title);
    return TRUE;
}

int main()
{
    int i = 0;
    ::printf("Starting EnumWindows()\n");
    ::EnumWindows(&MyEnumWindowsProc, reinterpret_cast<LPARAM>(&i));
    ::printf("EnumWindows() ended\n");
    return 0;
}

gives me an output like this:

Starting EnumWindows()
Window #1 (<hwnd>): <title>
Window #2 (<hwnd>): <title>
Window #3 (<hwnd>): <title>
<and so on...>
EnumWindows() ended

So EnumWindows() definitely enumerates in a synchronous manner.