Dynamic memory allocation in C

[Devendra Mandan]

I didn't understand that in dma ,are we required to have an initial guess of the memory needed or the calloc function allocates it as we need more of it i.e; what if our guess was not correct?

[Banfa]

You aren't required to "have a guess". You are required to know exactly how much memory you require.

If you don't know how much you need right now then either

1. You are trying to allocate memory too early
2. You know you need X bytes now you might need more later. Then allocate X bytes and set your data structures up so that later you can allocate more if required.