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In C, the library function malloc is used to allocate a block of memory on the heap. The program accesses this block of memory via a pointer that malloc returns. When the memory is no longer needed, the pointer is passed to free which deallocates the memory so that it can be used for other purposes.
The “malloc” or “memory allocation” method in C is used to dynamically allocate a single large block of memory with the specified size. It returns a pointer of type void which can be cast into a pointer of any form.
The malloc function allocates a memory block of at least size bytes. The block may be larger than size bytes because of the space that's required for alignment and maintenance information. malloc sets errno to ENOMEM if a memory allocation fails or if the amount of memory requested exceeds _HEAP_MAXREQ .
All variables allocated by malloc (or new in C++) is stored in heap memory. When malloc is called, the pointer that returns from malloc will always be a pointer to “heap memory”. All variables used as local variables – for example, when you just do int i = 0; – is stored on a function's stack.
Possible Duplicate:
How do free and malloc work in C?
Consider a scenario where i have to allocate some 20 bytes of memory through malloc. For the function call to malloc() to be successful, should the 20 bytes be available contiguously in memory or can it be scattered? For eg, in the above case, if there are 4 or 5 chunks of 10 bytes each, will malloc work? Or is this OS specific or compiler-specific?
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