Do you specifically need malloc to allocate memory to new elements of a linked list

Question

So, as far as I know, malloc returns a pointer to a location in the heap.

sbrk() expands the heap by a minimum of 4k

If I could not use malloc, for reasons, would it be possible in c to allocate memory to a new member if a linked list (for example) by using an adress withing that 4k that has been gained by an sbrk() call, instead of a malloc?

Sorry if this is a dmub question :(

EDIT: The reason I can't use malloc is because my task is to create my own malloc and am told to use sbrk.

Answer 1

brk and sbrk have been removed from POSIX; they are not portable. Some malloc implementations use sbrk, but don't necessarily expect application code to be moving the break address, and so using sbrk can break malloc. Even if your code doesn't use malloc, you might not be able to get away with breaking malloc, because some other code in your process might be calling it.

To obtain pages memory more directly from the operating system kernel relative to malloc in a modern POSIX environment, a better choice is the mmap function (with MAP_ANON and MAP_PRIVATE flags).

Answer 2

brk and sbrk are an alternative (deprecated) way of allocating heap memory instead of using malloc. In general, you should never use them in a program that uses malloc, but if your program never uses malloc (and never uses any stdlib functions that use malloc, such as stdio), you can use them instead to manage the heap.

sbrk can be used like malloc to allocate some additional heap space (the amount specified by its argument). brk can be used like free, except it frees the block specified AND EVERYTHING ALLOCATED AFTER IT by later calls to sbrk.