I'm new to boost::variant and I can't seem to use it in a class because I get linker errors. I can't find any reference to this in the archive or the docs so I figure it must be something silly I'm missing. Any help appreciated. The compilation command, error, and files are shown below. Thanks, Kevin Martin g++ -I $BOOSTINC test.cpp a.cpp /usr/lib64/gcc-lib/x86_64-suse-linux/3.3.5/../../../../x86_64-suse- linux/bin/ld: ` .gnu .linkonce .t ._ZN5boost6detail7variant15visitation_implIN4mpl_4int_ILi0EEENS1_20visitation_impl_stepINS_3mpl6l_iterINS7_6l_itemINS3_5long_ILl2EEEiNS9_INSA_ILl1EEESsNS7_5l_endEEEEEEENS8_ISD_EEEENS1_9destroyerEPvNS_7variantIiSsNS1_5void_ESM_SM_SM_SM_SM_SM_SM_SM_SM_SM_SM_SM_SM_SM_SM_SM_SM_E18has_fallback_type_EEEN7Visitor11result_typeEiiRSP_T2_NS3_5bool_ILb0EEET3_PT_PT0_ ' referenced in section `.rodata' of /tmp/ccZwRSZE.o: defined in discarded section ` .gnu .linkonce .t ._ZN5boost6detail7variant15visitation_implIN4mpl_4int_ILi0EEENS1_20visitation_impl_stepINS_3mpl6l_iterINS7_6l_itemINS3_5long_ILl2EEEiNS9_INSA_ILl1EEESsNS7_5l_endEEEEEEENS8_ISD_EEEENS1_9destroyerEPvNS_7variantIiSsNS1_5void_ESM_SM_SM_SM_SM_SM_SM_SM_SM_SM_SM_SM_SM_SM_SM_SM_SM_E18has_fallback_type_EEEN7Visitor11result_typeEiiRSP_T2_NS3_5bool_ILb0EEET3_PT_PT0_ ' of /tmp/ccZwRSZE.o The files are: ==== a.h ==== #ifndef __A_HEADER__ #define __A_HEADER__ #include <boost/variant.hpp> #include <string> class A { boost::variant<int, std::string> a; public: void setToString(const std::string &x); void setToInt(int x); int which() const; }; #endif ==== a.cpp ==== #include "a.h" int A::which() const { return this->a.which(); } void A::setToString(const std::string &x) { this->a = x; } void A::setToInt(int x) { this->a = x; } ==== test.cpp ==== #include "a.h" #include <iostream> int main() { A a; a.setToString("abc"); std::cout << a.which() << std::endl; a.setToInt(123); std::cout << a.which() << std::endl; return 0; }