[TUHS] Question about early C behavior.

[Warner Losh]

On Fri, Jan 10, 2020, 1:55 PM Derek Fawcus <dfawcus+lists-tuhs at employees.org>
wrote:

> On Fri, Jan 10, 2020 at 02:07:53PM -0500, Dan Cross wrote:
> >
> > My colleague was particularly surprised that this seemed required: even
> at
> > this early stage, the `extern` keyword was present, so why bother with
> this
> > behavior? Why not, instead, make it a link-time error? Please note that
> if
> > two source files have initializers for these variables, then one gets a
> > multiple-definition link error. The 1988 ANSI standard made this an error
> > (or at least undefined behavior) but the functionality persists; GCC is
> > changing its default to prohibit it (my colleague works on clang).
>
> This behaviour differed between platforms, unix using the common approach,
> and some other platforms simplying making it a (non common) symbol in the
> bss.
>
> Having learnt C in its pre-ANSI form on unix, I then ran in to this
> behaviour
> on DOS C compilers.  None of which (that I came across) providing the
> 'common'
> behaviour.
>

Gcc offered warnings for this behavior in the early 90s, iirc. I went
through a bunch of code in that time frame to remove the assumption...

Warner

>
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