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Subject: Re: Environment Variables
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Date: Sat, 07 Aug 2004 01:01:44 GMT
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Brian Inglis wrote:
> in comp.os.msdos.djgpp, "Eli Zaretskii" <eliz AT gnu DOT org> wrote:
> 
>>> From: CBFalconer <cbfalconer AT yahoo DOT com>
>>> Newsgroups: comp.lang.c,comp.os.msdos.djgpp
>>> Date: Thu, 05 Aug 2004 23:27:28 GMT
>>>
>>> Changing the 'environ' name makes things become correct.  gcc
>>> seems to be creating a parameter to main, which is being accessed
>>> by the identifier environ, even though the parameters are
>>> specified to be void. gcc -E creates no reference to 'environ'.
>>
>> `environ' is a symbol that comes from the library.  It is a pointer to
>> an array of char *, where each array element is a string of the form
>> "foo=bar": these are the environment variables and their values.
>>
>> I guess if this happens even under "-ansi -pedantic", it's a bug that
>> we pollute the ANSI namespace with a non-ANSI symbol that doesn't bgin
>> with an underscore.  But given that Unix programs expect that symbol,
>> I'm not sure we can change that.
> 
> FWIW below is a list of library symbols that pollute the user global
> namespace in *ALL* C programs and are not mentioned in the libc
> documentation.
> It was produced by compiling and linking a small dummy program, then
> running nm -Cg, stripping the addresses, and editing out the
> documented names.
> The first letter tells you whether it's defined in a text, data or bss
> segment.
> 
> D djgpp_first_ctor
> D djgpp_first_dtor
> D djgpp_last_ctor
> D djgpp_last_dtor
> D edata
> B end
> B environ
> T etext
> B exception_stack
> T start
> 
> ISTM that a reasonable first step would be to document the existence
> of these symbols in the libc documentation, and possibly add useful
> public interfaces to some header file, perhaps only for the case of
> environ, which seems to be the only symbol likely to be accessed by
> user level code.

... snip possible djgpp temporary fix ...

I am taking the liberty of crossposting this to c.l.c, where the
problem originally arose, with follow-ups set to c.l.c.  I think
this is appropriate because you have created a generalized method
of seeing the extent of the problem, for which thanks, at least in
the unix/posix world.

-- 
"The most amazing achievement of the computer software industry
 is its continuing cancellation of the steady and staggering
 gains made by the computer hardware industry..." - Petroski