Jon Steinhart <jon(_at_)fourwinds(_dot_)com> wrote:
Jon Steinhart <jon(_at_)fourwinds(_dot_)com> writes:
3. If the $HOME environment variable is set, mypath is copied from the
getenv return. Why? It's never changed.
4. If the $HOME environment variable is not set, mypath is copied from the
pw_dir member of the returned passwd structure. Now, I understand that
this is a static structure, but getpwuid is never called again so I
don't see why the copy is needed.
4. If the $HOME environment variable is not set, the pw_dir member of the
passwd structure returned by getpwuid() is checked for a NULL pointer.
This can never happen in a non-error return, which is already checked.
So why the superfluous check?
These checks are not superflous, they are for maintainability.
Two years from now someone will add a second getenv(3) call and
waste their (probably volunteer) time trying to figure out how
they busted the home dir variable. That is why, unless you are
writing super-tight-must-be-the-best-performing-code-ever
applications (which mh is not), it is necessary always to make a
copy of the static buffer pointed to by the return values of such
functions.
--
Eric Gillespie <*> epg(_at_)pretzelnet(_dot_)org
This is one of those places where we'll have to respectfully disagree. I'm
obviously in the minority given the quality of software that I see these days,
but I think that programming is still something that should be done by
professionals. I don't want someone hacking on code that doesn't take the time
to figure out what's going on first. Protecting against the really silly
mistakes allows such people to make really complex ones. As I said in my
earlier email, I'm not going to write slow and sloppy code just because
computers are fast. Matter of fact, I keep on trying to get up the courage
to tackle m_getfld().
Oh, some details.
1. A second getenv() call would not break the code. The copy was really
unnecessary.
2. It's hard for me to imagine a situation where getpwuid() would #1 get
called a second time and #2 for a different uid, which is the only that
a problem would occur.
The assumption that there will not be another getpwuid(), nor a
getpwnam(), is a horrible assumption, particularly from somebody who
has just commented about sloppy code. Your comment about "a different uid"
is also confused -- there is no certainty that a second call for the
same uid will return the same result, and it is sloppy programming
to assume that it will.
Presumably the copy following getenv() is for consistency between
the two cases (getenv() or getpwuid()).
-NWR