Creating a portable library to run on both linux and windows

Question

gcc (GCC) 4.7.2

Hello,

I am creating a shared library that will compile on linux and a dll that will compile on windows using the same sour

Answer 1

For Linux, gcc without -fvisibility=hidden will make functions exported by default, except for static functions.

With -fvisibility=hidden, gcc will make no functions exported by default, except that functions decorated by

__attribute__ ((visibility ("default")))

For Windows, exported functions decorated by

__attribute__ ((dllexport))

when using the exported functions, they must be decorated by

__attribute__ ((dllimport))

The macros in your posts

__declspec(dllexport)

are supported by MSVC.

So the crossed linux and windows macros are as following:

#if defined _WIN32 || defined __CYGWIN__ || defined __MINGW32__
  #ifdef BUILDING_DLL
    #ifdef __GNUC__
      #define DLL_PUBLIC __attribute__ ((dllexport))
    #else
      #define DLL_PUBLIC __declspec(dllexport) // Note: actually gcc seems to also supports this syntax.
    #endif
  #else
    #ifdef __GNUC__
      #define DLL_PUBLIC __attribute__ ((dllimport))
    #else
      #define DLL_PUBLIC __declspec(dllimport) // Note: actually gcc seems to also supports this syntax.
    #endif
  #endif
  #define DLL_LOCAL
#else
  #if __GNUC__ >= 4
    #define DLL_PUBLIC __attribute__ ((visibility ("default")))
    #define DLL_LOCAL  __attribute__ ((visibility ("hidden")))
  #else
    #define DLL_PUBLIC
    #define DLL_LOCAL
  #endif
#endif

• Make sure that shared object or DLL projects must be compiled with -DBUILDING_DLL.
• The project that depends on your shared object or DLL must be compiled without -DBUILDING_DLL

For the more details, please read http://gcc.gnu.org/wiki/Visibility