Questions on exporting functions from a shared library

[Jef Driesen]

I have a cross platform (win32/unix) project that consist of a C library 
and a few example applications using that library. The entire project is 
build with autotools. With the instructions from the online autotools 
book [1], I managed to build both a Windows DLL and a Unix shared 
library. But right now, every non-static function is exported. I would 
like to limit that to only the functions that are part of the public api.

It appears there are two options to do that:

1. Using dllexport/dllimport in the source code.

2. Using a DEF file during linking (with -export-symbols flag).

What are the (dis)advantages of each method? I see differences in usage 
(see below), but are there technical differences as well?

The first one seems to be the most complicated method, because you need 
to be able to distinguish between static/shared library builds, and 
export/import in the case of a shared library.

For the second one, you need to maintain a separate list of all the 
public functions. However in my case, this list is not static and can 
change depending on a number of external factors that are detected in 
the configure script (such as the target platform). I found a solution 
for that by #ifdef's in the file and running the C preprocessor over it.

Note: It should also be possible to compile the dll with an msvc 
compiler on Windows, and link a mingw32 compiled dll in an msvc 
application. I don't know if that makes a difference.

[1] http://sourceware.org/autobook/autobook/autobook_251.html#SEC251