Comment by aa-jv

2 days ago

Actually, no. You've just committed one of the cardinal sins of the *alloc()'s, which is: NULL is an acceptable return, so errno != 0 is the only way to tell if things have gone awry.

The proper use of realloc is to check errno always ... because in fact it can return NULL in a case which is not considered an error: lines is not NULL but requested size is zero. This is not considered an error case.

So, in your fix, please replace all checking of tmp == NULL, instead with checking errno != 0. Only then will you have actually fixed the OP's unsafe, incorrect code.

3 comments

aa-jv

spiffyk 2 days ago

From `malloc(3)`:

   Nonportable behavior
       The  behavior of these functions when the requested size is zero is glibc specific; other implementations may return NULL without setting errno, and portable POSIX programs should tolerate such behavior.  See realloc(3p).

       POSIX requires memory allocators to set errno upon failure.  However, the C standard does not require this, and applications portable to non-POSIX platforms should not assume this.

anymouse123456 2 days ago

As someone writing C for POSIX and embedded environments, this clarification is a super helpful.

cozzyd 2 days ago

In this case if (num_lines+1)(sizeof (char)) is zero that is certainly unintended