For example, I can't install package
qcad because of error: "can't find qdict.h".
How can I find the package which provides the file
qdict.h so I can install the package
You may use the
e-file command from the
pfl package (
emerge -av app-portage/pfl) to search by package contents.
Alternatively, you may use an online database.
qcad package specifically, you probably need the Qt4 package. IIRC, use
emerge -av x11-libs/qt-gui (If that doesn't work out, try searching for QT packages. Use this query:
emerge -s qt.)