No they're not absolutely the same. While both let you store the same number and type of objects, keep in mind that:
- You can
free() a malloced array, but you can't free() a variable length array (although it goes out of scope and ceases to exist once the enclosing block is left). In technical jargon, they have different storage duration: allocated for malloc versus automatic for variable length arrays.
- Although C has no concept of a stack, many implementation allocate a variable length array from the stack, while
malloc allocates from the heap. This is an issue on stack-limited systems, e.g. many embedded operating systems, where the stack size is on the order of kB, while the heap is much larger.
- It is also easier to test for a failed allocation with
malloc than with a variable length array.
- malloced memory can be changed in size with
realloc(), while VLAs can't (more precisely only by executing the block again with a different array dimension--which loses the previous contents).
- A hosted C89 implementation only supports
malloc().
- A hosted C11 implementation may not support variable length arrays (it then must define
__STDC_NO_VLA__ as the integer 1 according to C11 6.10.8.3).
- Everything else I have missed :-)
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