Question

I am passing a pointer to a string to a DialogProc via CreateDialogParam. This pointer points to dynamically allocated memory which is released immediately after CreateDialogParam returns. Is WM_INITDIALOG processed before CreateDialogParam returns?

For example:

LPWSTR lpStr = malloc( some_size )
CreateDialogParam( ... lpStr );
free( lpStr );

In DialogProc:

case WM_INITDIALOG:
  ... do something with lParam

Answer 1

Yes. According to the documentation for CreateDialogParam,

The CreateDialogParam function uses the CreateWindowEx function to create the dialog box. CreateDialogParam then sends a WM_INITDIALOG message … to the dialog box procedure.

The operative word here is that it sends a message (as opposed to posting one). SendMessage just calls the dialog procedure directly. PostMessage would put the message in the queue.

So, yes, the WM_INITDIALOG should complete before CreateDialogParam returns. You can verify this yourself relatively trivially using a debugger and some breakpoints.