| re: "extern" for the same file leads to wrong result. bug or feature?
Uenal Mutlu wrote:[color=blue]
> If "extern" is specified for a variable which is already in the same cpp file
> then the compiler (VS6) creates a new instance of the var in each thread.[/color]
Threads are not defined by C++ _language_. You will find more information
in comp.programming.threads or in microsoft.public.vc.language.
[color=blue]
> Is this a bug or a feature?[/color]
Unknown.
[color=blue]
> Which is standard conform?[/color]
Nothing. Or both. Threads are not part of the Standard, so whatever
happens is fine by it.
[color=blue]
>
> Example:
>
> test.cpp:
> int gi = 0;[/color]
This declares an object 'gi' that (by default) has external linkage.
[color=blue]
> test.cpp (ie. same file)
>
> thread_func(...)
> {
> extern int gi;[/color]
This is another declaration of 'gi'. This 'gi' is the same 'gi' as you
declared and defined outside of any function.
[color=blue]
> gi++;
> //...
> }
>
> thread1 starts and exits. gi now 1 as expected.
> thread2 starts and exits. gi now has value 1. Shouldn't it be 2 ?[/color]
Unknown. Threads are not defined by the language.
[color=blue]
> If the "extern" declaration is not used then gi is 2.
> Or, if the "extern" declaration is used and gi is moved to another cpp
> then too is gi 2.
>
> What's the correct (std conform) behaviour?[/color]
Either. Both. Unknown. The use of threads introduces the conditions
that C++ Standard cannot account for.
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