Is struct addrinfo **res allocated when getaddrinfo() returns a non-zero value?

Question

I am having some memory leaking troubles in an embedded application and while looking in the code, I see I do not freeaddrinfo() when getaddrinfo() returns non-zero:

s = getaddrinfo(hostname, port, &hints, &result);
if (s != 0) {
  log_error();
} else {
  // do stuff
  freeaddrinfo(result);
}

Could this lead to memory leaks? I have tried to look into the man page, but it doesn't state it explicitly.

Answer 1

The specification doesn't say that result isn't assigned if it fails, so it appears that a conforming implementation could do so.

Why not free it unconditionally?

result = 0;
s = getaddrinfo(hostname, port, &hints, &result);
if (s) {
    // log error
} else {
    // success
}
if (result) {
    freeaddrinfo(result);
}

Ideally you'd be able to call freeaddrinfo(result) without checking whether result is NULL, but although it's implied by the standard that that's OK I wouldn't count on it.

Answer 2

While it's true that the standard is a little bit vague about that, the only interpretation that makes sense is to treat the error as an alternative to a result. This is how other libc functions work and this is how getaddrinfo() is used in the examples even in the standard.

See: http://pubs.opengroup.org/onlinepubs/9699919799/functions/freeaddrinfo.html

I don't think there is a need to invent ways to get around that unless you're dealing with a known broken implementation. POSIX functions don't require you to zero the pointers used for output unless specified otherwise.

From the above link:

Upon successful return of getaddrinfo(), the location to which res points shall refer to a linked list of addrinfo structures, each of which shall specify a socket address and information for use in creating a socket with which to use that socket address.

It's pretty clear that the standard is written with an assumption that in other cases, the res variable is not being touched.