No ; you don't cast the result, since:
- It is unnecessary, as
void *is automatically and safely promoted to any other pointer type in this case.
- It adds clutter to the code, casts are not very easy to read (especially if the pointer type is long).
- It makes you repeat yourself, which is generally bad.
- It can hide an error if you forgot to include
<stdlib.h>. This can cause crashes (or, worse, not cause a crash until way later in some totally different part of the code). Consider what happens if pointers and integers are differently sized; then you're hiding a warning by casting and might lose bits of your returned address. Note: as of C99 implicit functions are gone from C, and this point is no longer relevant since there's no automatic assumption that undeclared functions return
As a clarification, note that I said "you don't cast", not "you don't need to cast". In my opinion, it's a failure to include the cast, even if you got it right. There are simply no benefits to doing it, but a bunch of potential risks, and including the cast indicates that you don't know about the risks.
Also note, as commentators point out, that the above talks about straight C, not C++. I very firmly believe in C and C++ as separate languages.
To add further, your code needlessly repeats the type information (
int) which can cause errors. It's better to de-reference the pointer being used to store the return value, to "lock" the two together:
int *sieve = malloc(length * sizeof *sieve);
This also moves the
length to the front for increased visibility, and drops the redundant parentheses with
sizeof; they are only needed when the argument is a type name. Many people seem to not know (or ignore) this, which makes their code more verbose. Remember:
sizeof is not a function! :)
length to the front may increase visibility in some rare cases, one should also pay attention that in the general case, it should be better to write the expression as:
int *sieve = malloc(sizeof *sieve * length);
Since keeping the
sizeof first, in this case, ensures multiplication is done with at least
malloc(sizeof *sieve * length * width) vs.
malloc(length * width * sizeof *sieve) the second may overflow the
length * width when
length are smaller types than