RE: Exporting const variables from DLLs (GCC bug?)

RE: Exporting const variables from DLLs (GCC bug?)

[Danny Smith]

Jon Foster wrote:

> Given this source code: 
> extern const int meaning_of_life __declspec(dllexport);
> const int meaning_of_life __declspec(dllexport) = 42;
> 
> 
> GCC complains: 
> $ c++ -g -O2 -c test.cxx -o test.o
> test.cxx:2: error: external linkage required for symbol 'const int
>    meaning_of_life' because of 'dllexport' attribute
>


It is a bug in gcc.  The above code compiles okay with C, but
strangely, not C++.  For some reason, g++ does not immediately
mark the the definition of global constants as public when they
are defined after a prior declaration.  I have a fix that I will
submit to gcc-patches after reg-testing

Danny

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Exporting const variables from DLLs (GCC bug?)

[Jon Foster]

Hi,

Given this source code:
> extern const int meaning_of_life __declspec(dllexport);
> const int meaning_of_life __declspec(dllexport) = 42;

GCC complains:
> $ c++ -g -O2 -c test.cxx -o test.o
> test.cxx:2: error: external linkage required for symbol 'const int
>    meaning_of_life' because of 'dllexport' attribute.

However, it compiles successfully with the "const" qualifier
removed:
> extern int meaning_of_life __declspec(dllexport);
> int meaning_of_life __declspec(dllexport) = 42;

Why does adding the "const" qualifier change this?  Is
this a known limitation of DLLs?  If so, the error message
is a little confusing.  If not, then this is a GCC bug.

Removing the explicit "extern" line has no effect in either
case.

My Cygwin installation was updated recently - I'm using the
standard Cygwin GCC 3.3.1-3 package:
> $ c++ --version
> c++ (GCC) 3.3.1 (cygming special)

If you want any more info, just ask.

Incidentally, this bug affects src/sid/component/ in the
Cygwin CVS tree.  I'd prepared this minimal test case before
I realized that this subdirectory isn't needed to build the
Cygwin DLL.  (Doh!  CVS doing unexpected things strikes again).

Kind regards,

Jon Foster





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