Hi there, I'm having some trouble with explicit template instantiation and inheritance using two instances of g++, and was wondering if someone a bit more wise could help me out. I read the fine explanation at http://gcc.gnu.org/onlinedocs/gcc/Template-Instantiation.html, but that doesn't seem to cover subclassing, which is where my problem (apparently) is. I'm building a library that includes an RTP component and an application that uses that library. One of the classes in the public interface of library has a member from the GNU ccRTP library: #include <ccrtp/rtp.h> class RTPAudioPort : public AudioPort { ... private: ost::SingleThreadRTPSession<ost::RTPBaseUDPIPv4Socket, ost::RTPBaseUDPIPv4Socket, ost::AVPQueue> *rtpSession; ... }; Now, I want to compile with -fno-implicit-templates if at all possible, because we're also compiling this library on Windows (visual c++ 2008), and it requires explicit template instantiation (from what searching I've done). I'm compiling with two different gcc toolchains, one native (i486-linux-gnu, g++ version 4.4.1) and one cross (arm-926ejs-linux-gnueabi, g++ version 4.3.4). So, I can compile the library just fine without template instantiation, and then when I try and compile an application that uses it, I get the expected sorts of errors from both linkers: undefined reference to `vtable for ost::SingleThreadRTPSession<ost::RTPBaseUDPIPv4Socket, ost::RTPBaseUDPIPv4Socket, ost::AVPQueue>' (and more of similar) My problem is exactly how/where I should instantiate my templates so that my RTPAudioPort class can be used by my application. I can keep the native-toolchain happy by placing my template instantiation (i.e. the line "template class ost::SingleThreadRTPSession<ost::RTPBaseUDPIPv4Socket, ost::RTPBaseUDPIPv4Socket, ost::AVPQueue>;") in that class's header file - that way, my library builds on the native toolchain and my application can also compile and link successfully. However, when I do this, the cross-toolchain complains when compiling the library (correctly, I think...?) because of multiple definitions: multiple definition of `typeinfo for ost::SingleThreadRTPSession<ost::RTPBaseUDPIPv4Socket, ost::RTPBaseUDPIPv4Socket, ost::AVPQueue>' (etc.) Alright, I probably shouldn't be putting that in a header file, so I try putting the instantiation in the source file. Now, both libraries compile, but when I try and use the library from my application, both toolchains complain of: undefined reference to `typeinfo for ost::TRTPSessionBase<ost::RTPBaseUDPIPv4Socket, ost::RTPBaseUDPIPv4Socket, ost::AVPQueue>' undefined reference to `VTT for ost::TRTPSessionBase<ost::RTPBaseUDPIPv4Socket, ost::RTPBaseUDPIPv4Socket, ost::AVPQueue>' undefined reference to `vtable for ost::TRTPSessionBase<ost::RTPBaseUDPIPv4Socket, ost::RTPBaseUDPIPv4Socket, ost::AVPQueue>' It turns out that ost::SingleThreadRTPSession is a direct subclass of ost::TRTPSessionBase (see http://gnu.gds.tuwien.ac.at/software/ccrtp/doc/refman/html/class_single_thread_r_t_p_session.html in the library's api). I notice the linker doesn't seem to be missing any function definitions or anything, just the vtable/VTT/typeinfo (or maybe it just doesn't get to needing them before it exits due to this error?). And that's basically where I'm at. I'd have thought that instantiating the subclass would also cause gcc to emit the necessary superclass info, as the native toolchain seems to do when I instantiate it in the header file. Can anybody point me to what I'm missing? Many thanks for reading! John G
