C ++共享库宏

Question

I have a C++ shared library. The library has files to be exported. I was using Qt, which makes it quite easy, but I can't use it anymore. So I need a pure C++ variant that covers it for Linux and Windows. So I came up with the following macro definitions.

Pure C++

#if defined(_WIN32) || defined(_WIN64) || defined(WIN32) || defined(WIN64)
    //  Microsoft
    #define MY_SHARED_EXPORT __declspec(dllexport)
#elif defined(__linux__) || defined(UNIX) || defined(__unix__) || defined(LINUX)
    //  GCC
    #define MY_SHARED_EXPORT __attribute__((visibility("default")))
#else
//  do nothing and hope for the best?
    #define MY_SHARED_EXPORT
    #pragma WARNING: Unknown dynamic link import/export semantics.
#endif

Qt C++

#if defined(MY_LIBRARY)
#  define MY_SHARED_EXPORT Q_DECL_EXPORT
#else
#  define MY_SHARED_EXPORT Q_DECL_IMPORT
#endif

Currently I'm using the Qt C++ variant. My question is if it is safe to replace the Qt variant, as seen above, with the pure C++ variant. And are they equivalent?

Any help is appreciated, thanks in advance.

Answer 1

It's safe to define your own import/export macros. But the one you posted is not equivalent to Qt one because you did not handle the import. It should be:

#if defined(_WIN32) || defined(_WIN64) || defined(WIN32) || defined(WIN64)
    //  Microsoft
    #if defined(MY_LIBRARY)
        #define MY_SHARED_EXPORT __declspec(dllexport)
    #else
        #define MY_SHARED_IMPORT __declspec(dllimport)
    #endif
#elif defined(__linux__) || defined(UNIX) || defined(__unix__) || defined(LINUX)
    //  GCC
    #if defined(MY_LIBRARY)
        #define MY_SHARED_EXPORT __attribute__((visibility("default")))
    #else
        #define MY_SHARED_IMPORT
    #endif
#else
//  do nothing and hope for the best?
    #define MY_SHARED_EXPORT
    #pragma WARNING: Unknown dynamic link import/export semantics.
#endif

I'm not 100% sure __attribute__((visibility("default"))) applies to Linux. In my mind, this was for iOS.

As commented by Rafael, the easiest is probably to simply go to Qt sources (qglobal.h) and copy/paste Q_DECL_EXPORT / Q_DECL_IMPORT from here to your own header file and then include it from your environment.