Mateusz Loskot wrote:
Christian Henning wrote:
2) I notice you saying that you're getting linker errors - that should only happen if you're taking the address of the constants somewhere - if that's a use case that you want to support, then you need a definition for the constants somewhere - suitably guarded by the right Boost.Config macros (sorry can't remember what off the top of my head). I'm getting a compiler error with gcc 3.4.5. The compiler that comes with MinGW.
Is it compiler error or linker error?
I did a simple test of the construction you use with GCC 4.4.1 and I'm getting linker error:
#include <boost/config.hpp> #include <cassert>
template<typename Property> struct property_base { typedef Property type; };
struct pnm_image_type : property_base<int> { typedef pnm_image_type self_type; BOOST_STATIC_CONSTANT( type, _mono_asc = 1 ); };
int main() { pnm_image_type imt; int const& r = pnm_image_type::_mono_asc; assert(1 == r); int const* p = &pnm_image_type::_mono_asc; assert(1 == *p); }
gcc.link bin/gcc-4.4.1/debug/static_const bin/gcc-4.4.1/debug/static_const.o: In function `main': /home/mloskot/workshop/boost/constants/static_const.cpp:17: undefined reference to `pnm_image_type::_mono_asc' /home/mloskot/workshop/boost/constants/static_const.cpp:18: undefined reference to `pnm_image_type::_mono_asc' collect2: ld returned 1 exit status
"g++" -o "bin/gcc-4.4.1/debug/static_const" -Wl,--start-group "bin/gcc-4.4.1/debug/static_const.o" -Wl,-Bstatic -Wl,-Bdynamic -Wl,--end-group -g
...failed gcc.link bin/gcc-4.4.1/debug/static_const... ...failed updating 1 target... ...updated 1 target...
This can be fixed, inconveniently, by adding external definition:
struct pnm_image_type : property_base<int> { typedef pnm_image_type self_type; BOOST_STATIC_CONSTANT( type, _mono_asc = 1 ); }; const int pnm_image_type::_mono_asc;
One more thing, I've just reminded than John has mentioned this issue already. Now, the question is, do you take address of any of these constants? Best regards, -- Mateusz Loskot, http://mateusz.loskot.net Charter Member of OSGeo, http://osgeo.org