Is the heap preallocated for a process

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Since I was introduced to the concept of heap of a process, I have been assuming that the OS allocates it at the creation of the process. But then I was doing some research and read a statement here. It says:

When a program asks malloc for space, malloc asks sbrk to increment the heap size and returns a pointer to the start of the new region on the heap.

If I understood what's been said, the OS allocates 0 cell for the process's heap, and it is only by calling malloc that the process gets some heap cells. And for me this makes more sens for the expression "dynamic allocation". Is this correct ?

malloc operating-system heap-memory
1 Answers

in figure you can see that your c/c++ program have a free memory area where the heap and the stack can grow until full the region, so Initialy the heap is empty, and when a process call malloc, Normally (but in modern implementation, malloc prefer to call always mmap()) he call the sbrk() function for increase the memory size of the heap (in reality he first search into the free linked list and if there is not any entry into the linked list he call sbrk(), see this for a implementation of malloc() malloc implementation?). So the os don't directly decide how the heap of a process should be allocated, in c/c++ the thinks work like this, but i think that in other languages the thinks can be slightly different.

Initialy the heap is empty

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