[GitHub] [logging-log4cxx] rm5248 edited a comment on issue #22: Only exporting the log4cxx symbols by default

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

rm5248 edited a comment on issue #22: Only exporting the log4cxx symbols by default
URL: https://github.com/apache/logging-log4cxx/pull/22#issuecomment-612049860
 
 
   In that case, there's probably an easier way to do this.  Since the symbols already need to be marked as exported for Windows builds, they already have a `LOG4CXX_EXPORT` macro associated with them.  This is not set to anything on [Linux/OSX builds](https://github.com/apache/logging-log4cxx/blob/671f0b5663b6b1063cfaa44acaee1b244fec3769/src/main/include/log4cxx/log4cxx.h.in#L46), but since the macro is there all you _should_ have to do is modify log4cxx.hw.in to look something like the following:
   
   ```
   #define LOG4CXX_EXPORT_SYMBOLS_ONLY @EXPORT_ONLY_LOG4CXX_SYMBOLS@
   
   #if LOG4CXX_EXPORT_SYMBOLS_ONLY
     #if __GNUC__ >= 4
         #define LOG4CXX_EXPORT __attribute__((visibility("default")))
     #else 
         #define LOG4CXX_EXPORT
     #endif
   #else
     #define LOG4CXX_EXPORT
   #endif
   ```
   
   And then add to the compilation flags `-fvisibility=internal`, something like this:
   
   ```
   if(BUILD_SHARED_LIBS AND EXPORT_ONLY_LOG4CXX_SYMBOLS)
     check_cxx_compiler_flag("-fvisibility=internal" LOG4CXX_SUPPORTS_VISIBILITY_INTERNAL)
     if( LOG4CXX_SUPPORTS_VISIBILITY_INTERNAL )
       set( LOG4CXX_COMPILE_OPTIONS ${LOG4CXX_COMPILE_OPTIONS} "-fvisibility=internal")
     endif( LOG4CXX_SUPPORTS_VISIBILITY_INTERNAL )
   endif()
   
   # ... in src/CMakeLists.txt
   target_link_libraries(log4cxx PRIVATE ${LOG4CXX_COMPILE_OPTIONS})
   ```
   
   Weather or not that will work appropriately/is a good idea, I don't know.

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