On 06/05/2013 06:36 AM, Colin Watson wrote: >> >> clearenv() is non-standard (it is a glibc extension); but yes, glibc >> documents that "environ = NULL" is a portable alternative. > > Hm, that's not in my libc.info. Do you just mean the code?
I found it in 'man clearenv' on a Linux system; so maybe that's in the man-pages project instead of the glibc project. > >> And yes, it is probably quite easy to write a gnulib module that would >> provide clearenv everywhere, although I fail to see why applications >> need the overhead of a function call when an assignment would do. > > I was wary about other C libraries that might assume that the environ > pointer can always be dereferenced; and e.g. > http://hg.dovecot.org/dovecot-2.0/file/74d9f61e224d/src/lib/env-util.c#l56 > has some specific portability notes which indicate that "environ = NULL" > isn't an adequate replacement everywhere. This is the kind of reason I > like to use Gnulib so that it can shield me from this nonsense, > especially if somebody discovers another OS with some newer crazy > requirement. :-) POSIX requires assignment to 'environ' to work when doing wholesale replacement of an environment, with one caveat - if your environment requires certain variables to exist to guarantee conformance (think POSIXLY_CORRECT or PATH, for example), then wholesale nuking of the environment may result in your program transitioning into a non-conforming setup, where things may misbehave compared to your expectations since you are no longer protected by POSIX guarantees. Thus, while 'environ = NULL' and 'clearenv()' do the same thing, neither of them is very wise compared to constructing an environment that preserves the essentials rather than stripping everything. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
signature.asc
Description: OpenPGP digital signature
