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RE[2]: Exporting const variables from DLLs (GCC bug?)

 --- Danny Smith <> wrote: > 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

On second thought, I don't think  I will.
In c++, const variables at namespace scope have internal linkage unless
declared with explicit extern (as you have done).  But I've just run this
testcase on gcc and VC and I get essentially the same error reports:

/* const.cpp */
/* 1: TREE_PUBLIC is set when dllexport attribute is handled. */
 __declspec(dllexport) int bar = 42;  // OK

/* 2: This is OK too. TREE_PUBLIC is set, because of 'extern' */
extern  __declspec(dllexport) const int baz;
const int baz = 42;  //OK 

/* 3: TREE_PUBLIC _not_  set. Nor should it be. consts are local 
   by default in c++ */
 __declspec(dllexport) const int foo = 42;  // ERROR

/* 4: TREE_PUBLIC _not_  set.  */
extern  __declspec(dllexport) const int faz;
__declspec (dllexport) const int faz = 42;  // ERROR

int fun()
{ return foo + faz; }

I thought that case 4 should be okay because of the 'extern' on declaration,
but if GCC wants to maintain consistency with native compiler, 4 should report
an error as well. The error mesage that VC emits is: error C2201: 'faz' : must
have external linkage in order to be exported/imported

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