[osg-users] Potential fix for osgDB MSVC linkage issues (FORCE:MULTIPLE needed)

[James Turner]

Hello,

With recent MSVC versions, we’re obliged to use /FORCE_:MULTIPLE, to work around the fact that osgDB.lib includes symbols from std::fstream classes, which then causes conflicts when other object files in a target (eg executable) being linked use <fstream> classes. This slows down linking since incremental linking is disabled, and makes our build output very noisy.

After some discussion, I came up with the following fix:

	https://github.com/zakalawe/osg/commit/2098c022283f1afeb4bad0ffb4b682b884cc8f32

The idea is to only export the non-inlined symbols from osgDB::ofstream and ::ifstream, but not to export the entire class, since doing so forces MSVC to also export the constructor and destructor for the base class (std::ofstream and std::ifstream).

Since we don’t use the osgDB versions of fstream in FlightGear, I can’t check if this is backwards compatible for other Windows OSG users, but I am hopeful that it is, and hence that this approach could be upstreamed. 

Kind regards,
James