Heap Memory in C Programming

Question

What exactly is heap memory?

Whenever a call to malloc is made, memory is assigned from something called as heap. Where exactly is heap. I know that a program in mai

Answer 1

The heap is part of your process's address space. The heap can be grown or shrunk; you manipulate it by calling brk(2) or sbrk(2). This is in fact what malloc(3) does.

Allocating from the heap is more convenient than allocating memory on the stack because it persists after the calling routine returns; thus, you can call a routine, say funcA(), to allocate a bunch of memory and fill it with something; that memory will still be valid after funcA() returns. If funcA() allocates a local array (on the stack) then when funcA() returns, the on-stack array is gone.

A drawback of using the heap is that if you forget to release heap-allocated memory, you may exhaust it. The failure to release heap-allocated memory (e.g., failing to free() memory gotten from malloc()) is sometimes called a memory leak.

Another nice feature of the heap, vs. just allocating a local array/struct/whatever on the stack, is that you get a return value saying whether your allocation succeeded; if you try to allocate a local array on the stack and you run out, you don't get an error code; typically your thread will simply be aborted.