Where does _EXPORTS comes from?

Question

I have seen many c++ header file under MSVC environment like this:

#ifdef somelib_EXPORTS
#define DLLEXPORTS __declspec(dllexport)
#else
#define DLLEXPORTS __declspec(dllimport)
#endif

Where does the <libname>_EXPORTS convention come from ?

Is it a Visual Studio's default macro ? Or is it generated by CMake ?

I can't find any document about this convention.

It is probably generated by the default project template included with Visual Studio. But it's just convention—it has no other meaning. You can use any name you want. See more generally: http://stackoverflow.com/questions/8863193/what-does-declspecdllimport-really-mean — Cody Gray - on strike, Jan 30 '17 at 16:23
Nothing to do with CMake, this convention has been in use well before that even existed. — Dan Mašek, Jan 30 '17 at 16:24
`CMake` documentation says that the default macro from `CMake` is `LIBNAME_EXPORT` https://cmake.org/cmake/help/v3.0/module/GenerateExportHeader.html however it's easy to change the default or the library may generate a similar header without using GenerateExportHeader. — drescherjm, Jan 30 '17 at 16:38

score 0 · Accepted Answer · answered Jan 30 '17 at 16:24

Where does the _EXPORTS convention come from ?

This is general coding guideline that helps with making sure that a .h file can be #included while building a DLL and by the users of the DLL.

The name DLLEXPORTS is project specific. It can be generated by CMake, qmake, or manually. I don't think Visual Studio can generate them, at least I haven't seen that.

If you have 10 DLLs in your project, you will end up using 10 such macros. For example, you might have UTILITY_DLL_EXPORT, MESSAGING_DLL_EXPORT, KERNEL_DLL_EXPORT, etc.

Where does _EXPORTS comes from?

1 Answers1