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Exporting const variables from DLLs (GCC bug?)
- From: Jon Foster <jon at jon-foster dot co dot uk>
- To: "cygwin at cygwin dot com" <cygwin at cygwin dot com>
- Date: Sun, 16 Nov 2003 18:59:29 +0000
- Subject: Exporting const variables from DLLs (GCC bug?)
Given this source code:
extern const int meaning_of_life __declspec(dllexport);
const int meaning_of_life __declspec(dllexport) = 42;
$ 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
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
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).
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