We have a fairly graphical intensive application that uses the FOX toolkit and OpenSceneGraph, and of course C++. I notice that after running the application for some time, it seems there is a memory leak. However when I minimize, a substantial amount of memory appears to be freed (as witnessed in the Windows Task Manager). When the application is restored, the memory usage climbs but plateaus to an amount less than what it was before the minimize.
Is this a huge indicator that we have a nasty memory leak? Or might this be something with how Windows handles graphical applications? I'm not really sure what is going on.
What you are seeing is simply memory caching. When you call free()/delete()/delete, most implementations won't actually return this memory to the OS. They will keep it to be returned in a much faster fashion the next time you request it. When your application is minimized, they will free this memory because you won't be requesting it anytime soon.
It's unlikely that you have an actual memory leak. Task Manager is not particularly accurate, and there's a lot of behaviour that can change the apparent amount of memory that you're using- even if you released it properly. You need to get an actual memory profiler to take a look if you're still concerned.
Also, yes, Windows does a lot of things when minimizing applications. For example, if you use Direct3D, there's a device loss. There's thread timings somethings. Windows is designed to give the user the best experience in a single application at a time and may well take extra cached/buffered resources from your application to do it.