Inserts a copy of the contents of src into dest at position index. index must be non-negative and no greater than the length of dest. Returns 0 if the function succeeded, or -1 if there was insufficient memory.
Inserts a copy of the characters referenced by chars into astr at position index. index must be non-negative and no greater than the length of dest. Returns 0 if the function succeeded, or -1 if there was insufficient memory.