[GitHub] [logging-log4cxx] geirg71 commented on issue #177: LOG4CXX_INSTANTIATE_EXPORTED_PTR issue on MSYS2 / GCC

[GitBox <gi...@apache.org>]

geirg71 commented on issue #177:
URL: https://github.com/apache/logging-log4cxx/issues/177#issuecomment-1383078063

   Thank you for the lightning fast response Stephen. Your 2 commits fix my problem on MSYS2.
   
   I do however ask you to look at the use of the LOG4CXX_INSTANTIATE_EXPORTED_PTR macro. Clang 14 on Linux complains about the same issue as GCC if I change the macro to the Windows variant (refer output below). Hence I guess the C++ standard really prohibits this type of template instantiations, and the issue could resurface later in e.g. future MSVC versions implementing the standard.
   
   For me both compilers are happy if I move LOG4CXX_INSTANTIATE_EXPORTED_PTR outside of the log4cxx namespace. Example from propertysetter.h, change: 
   
   ```
   #include <log4cxx/logstring.h>
   #include <log4cxx/helpers/object.h>
   
   namespace log4cxx
   {
   namespace helpers
   {
   class Object;
   // Instantiate template pointer type passed as parameter
   LOG4CXX_INSTANTIATE_EXPORTED_PTR(Object);
   LOG4CXX_PTR_DEF(Object);
   ```
   
   to
   
   ```
   #include <log4cxx/logstring.h>
   #include <log4cxx/helpers/object.h>
   
   // Instantiate template pointer type passed as parameter
   LOG4CXX_INSTANTIATE_EXPORTED_PTR(log4cxx::helpers::Object);
   
   namespace log4cxx
   {
   namespace helpers
   {
   class Object;
   LOG4CXX_PTR_DEF(Object);
   ```
   
   Clang 14 on Ubuntu 22.04 with #define LOG4CXX_INSTANTIATE_EXPORTED_PTR(T) template class LOG4CXX_EXPORT std::shared_ptr<T>:
   ```
   $ clang++ --version
   Ubuntu clang version 14.0.0-1ubuntu1
   Target: x86_64-pc-linux-gnu
   Thread model: posix
   InstalledDir: /usr/bin
   
   [build] /usr/bin/clang++  -Ilogging-log4cxx/src/test/cpp/util -Ilogging-log4cxx/build/src/main/include -Ilogging-log4cxx/src/main/include -I/usr/include/apr-1.0 -g -std=c++17 -MD -MT src/test/cpp/util/CMakeFiles/testingUtilities.dir/compare.cpp.o -MF src/test/cpp/util/CMakeFiles/testingUtilities.dir/compare.cpp.o.d -o src/test/cpp/util/CMakeFiles/testingUtilities.dir/compare.cpp.o -c logging-log4cxx/src/test/cpp/util/compare.cpp
   [build] In file included from logging-log4cxx/src/test/cpp/util/compare.cpp:23:
   [build] logging-log4cxx/src/main/include/log4cxx/helpers/inputstreamreader.h:32:1: error: explicit instantiation of 'shared_ptr' not in a namespace enclosing 'std'
   [build] LOG4CXX_INSTANTIATE_EXPORTED_PTR(InputStream);
   [build] ^
   [build] logging-log4cxx/build/src/main/include/log4cxx/log4cxx.h:94:80: note: expanded from macro 'LOG4CXX_INSTANTIATE_EXPORTED_PTR'
   [build] #define LOG4CXX_INSTANTIATE_EXPORTED_PTR(T) template class LOG4CXX_EXPORT std::shared_ptr<T>
   [build]                                                                                ^
   [build] /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/bits/shared_ptr.h:175:11: note: explicit instantiation refers here
   [build]     class shared_ptr : public __shared_ptr<_Tp>
   ```


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