Adding a new file to VisIt's source code is requires 2 steps after you create the file.
- Add the file to SVN by running: svn add file.C
- Make the build system aware of the new file. Chances are you are adding a new file to an existing library so you will just need to modify the CMakeLists.txt file for the library that contains your new file. Adding the file to the CMakeLists.txt file amounts to little more than adding the name of the file to an existing list of source files. You will need to rerun cmake to regenerate the files that build VisIt.