Truncating a locked file

[Patrick Hertel]

 How can I truncate a file which I have locked (mandatory) with lockf.
That is to say I open then lock then read and now I want to truncate
without letting go of the lock, all in the same program. Oh, this is
a C program by the way.
-- 
Pat Hertel                 Canadian Meteorological Centre
Analyst/Programmer         2121 N. Service Rd.
phertel at cmc.aes.doe.ca     Dorval,Quebec
Environment Canada         CANADA           H9P1J3