Presently I copy the .h and .cpp files containing general purpose functions into each project directory, and everything compiles and links nicely. However, if I try to #include the .h file when it is placed in a different directory, I get a the following 2 errors:
error LNK2001: unresolved external symbol ......
and
fatal error LNK1120: 1 unresolved externals

This occurs if I #include the absolute path, both with and without quoted backslash, and whether or not I add the path to (all sections of ) the Tools:Optionsirectories.

I can't believe that there is not a way to include source files which are in some user-defined common directory.