Memory is added to the heap or taken from the heap?

[Ankit Khare]

We say that in a C process' memory layout,the heap segment deals with the dynamic memory allocation i.e. malloc,calloc.

When we do

int *p=malloc(100000);

100000 bytes are :
1.taken from the system memory and whole 100000 bytes added into the process' heap memory segment

2.taken from the process' heap memory(process' heap already had this memory,it has turned accessible now )

3.taken from the system memory and address to that memory is added to the heap segment of the process.So p actually points to 100000 bytes in the system memory.
????

[weaknessforcats]

C does not require a heap or a stack. Heaps and stacks are implementation defined so they vary by operating system.

Usually a process is allowed a ration of memory while it's running. This is the process heap and it is allocated from system memory by OS when the process is created. From this the CRT (C-run-time) heap may be allocated (depends).

Windows programmers often create a private heap and use Windows allocators to allocate from that heap and then delete the heap when they are finished. This avoids malloc/free and all the leaks.

Memory management is a big deal and you need to read specfically for your situation.

Fortunately, you can view the heap as memory you control so that you can store stuff and be sure it doesn't get away from you until you are done with it

[Ankit Khare]

Ohk,let me put it this way,we say that the "heap grows". What exactly is meant by that?
**If, on doing malloc(), memory is taken from the heap then why do we say that the heap grows?

[donbock]

Personally, I would not say "the heap grows".
Where are you seeing that phrase? In what context?

[Banfa]

The process heap can grow.

While a process is running it memory gets allocated from its heap. That doesn't mean that the processes heap gets smaller when the memory is allocated just that there is less free space in the heap.

On a number of modern operating systems (Windows and Linux to name 2) if a process runs out of heap space then rather than fail at the next allocation it can increase the amount of memory available on its heap by requesting additional memory from the system to assign to its heap.

In this sense a programs heap can grow, that is the amount of memory allocated to the processes heap can increase during the lifetime of the process.

Note that this is a function of the operating system as mentioned C does not even require that there be a heap and in, for example, an embedded environment the processes heap is fixed at link time because normally in an embedded environment RAM is a scarce resource.