On Mon, 2002-11-18 at 22:47, Eric Gillespie wrote: > Jon Steinhart <[EMAIL PROTECTED]> 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.
The return value of getenv() is a pointer into the environment; a future getenv() call will not overwrite it. So it's safe not to copy it unless you anticipate a putenv(). (And I think it's safe even in the face of a putenv(), actually.) A judgement call. Your argument definitely holds for copying the getpwuid() value. Checking the pw_dir element for NULL is superfluous unless you feel like second-guessing the kernel and libc at every turn, a practice which doesn't have much value.
