No, only global variables are zero-initialized. Neither stack variables nor malloced memory will be zero-initialized. OP should have memset to 0 or calloced the memory.
> He's assuming that dest is zero-initialized, which I believe it will be as written.
Given this snippet, incorrect. Stack allocated buffers aren't zeroed out as in the above declaration.
edit: As asveikau notes below, this is not the case