C / C++ / MFC

Frederick J. Harris wrote:

How do you get the number of bytes actually written to a Stream as opposed to the total allocation for the Stream?

1. Add the following lines on top of one of your cpp files:
   
   C++

   #pragma data_seg("shared")
   LONG g_counter = 0; // This variable is allocated on a page shared between processes...
   #pragma data_seg()
   
   #pragma comment(linker, "/section:shared,rws")

2. Execute the following instruction as soon as possible at startup of your application:
   
   C++

   InterlockedIncrement(&g_counter);

3. Execute the following instruction immediately before exiting from your application:
   
   C++

   InterlockedDecrement(&g_counter);

4. When you need the number of instance of your application currently running, use this code:
   
   C++

   LONG instances = InterlockedExchangeAdd(&g_counter, 0);