For Standard Make projects you can define include paths and preprocessor symbols for the parser. This enables the parser to understand the contents of the C/C++ source code so that you may more effectively use the search and code completion features.
If Autodiscovery is enabled once a build has completed any discovered paths and symbols will be displayed in the Discoverd Paths section. You can also define the properties on a per project basis in the C/C++ Projects or Navigator views.
To add include paths and symbols:
CDT Projects
Project file views
Working with C/C++ project files