Code completion is not perfect, but it normally works quite well with these constraints:
1. header files on the hard disk are scanned, not in-memory
2. No project = no code completion. Source or header not part of the project = no code completion.
3. no std:: classes, no STL
4. namespaces do work, but the keyword using is not implemented yet
5. it must have finished parsing before it is any good - this can take up to 10-15 seconds on a large project