Why would you ever want to allocate memory on the heap rather than the stack? [duplicate]

Answer 1

1. You want an allocation to live beyond a function invocation
2. You want to conserve stack space (which is typically limited to a few MBs)
3. You're working with re-locatable memory (Win16, databases, etc.), or want to recover from allocation failures.
4. Variable length anything. You can fake around this, but your code will be really nasty.

The big one is #1. As soon as you get into any sort of concurrency or IPC #1 is everywhere. Even most non-trivial single threaded applications are tricky to devise without some heap allocation. That'd practically be faking a functional language in C/C++.