If you're not set on "rolling your own", there are existing Open Source packages that may do what you're looking for.

I use Analog and Webalizer myself. Both are available as source or binaries for *nix, Win32, etc. I can't say for sure if they deal with whatever logfile format IIS 4 uses, though.
    cheers,
    ybiC

In reply to RE: Parsing a log file (analog, webalizer) by ybiC
in thread Parsing a log file by Anonymous Monk

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