Atomic file truncation

[Scott Thompson]

I want to read, process and write, a possibly smaller (truncate), mail
file in a single locked open.

Currently I can read, process and write the file originally opened
with fopen and "r+", but it will not truncate if the new file is
shorter; I also tried other combinations along with open, but they
truncate the file prior to reading!  This is for use under SYSV for
file locking a mail file.

Any and all suggestions will be appreciated.

Thanks
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  Scott Thompson (IH 6W-207), AT&T Bell Labs, Naperville, Il. 60566

       VOICE: (312)-979-2237     UUCP: ...!att!ihlpa!sft