More info on this one: I tried commenting out the compare_exchange() fn and the forwarding fns it uses and switched to directly calling InterlockedExchangeCompare() in boost/thread/src/once.cpp and this fixed the problem. I also see the error in a vanilla boost build for AMD64 Windows - has anyone tested this code on 64-bit Windows? I suppose it's a compiler bug as (although I'm not completely sure) it knows that the address of the fn is only used in inline fns that call it. Also it seems to compile OK on the IA64 compiler without this change. Bill Somerville On 20 Mar 2006, at 16:15, Bill Somerville wrote: Hi I'm having trouble linking a program that uses boost::call_once() on a Windows AMD64 machine. I get a link error saying _InterlockedCompareExchange() is undefined - this should be an intrinsic function on this platform but I think the code in thread/src/once.cpp where the address is taken of the intrinsic function has fooled the development system. It works OK on IA64 were the function is also intrinsic. We are building statically so it's possible that we are not passing some compiler switch that fixes this - but I don't see it. Has anyone else hit this problem with 64-bit AMD64 code and boost::call_once() on Windows? Compiler version is: Microsoft (R) C/C++ Optimizing Compiler Version 14.00.40121 for AMD64 Bill Somerville _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users