The detail I'm concerned about -- and it may not be a problem because I may be overlooking something -- is that the string I'm matching against can have zero or one 'C' field and zero or one 'O' fields. It looks like the "C(\\d+)|O(\\w+)" expression will match either of them if at least one is present, but after that, I would need optionally to match the other one. Matching the same field again would be an error. In other words: ~C12345~OF <-- valid (1 of each) ~OF <-- valid (1 'O' field) ~C12345 <-- valid (1 'C' field) ~ZAQ~C12345 <-- valid (1 'C' field) ~OV~C67890 <-- valid (1 of each) ~A23~OV~DFG~C67890~ZAQ <-- valid (1 of each) ~A23~DFG <-- valid (neither) ~C12345~OF~C67890 <-- invalid (2 'C' fields) ~C12345~OF~OV <-- invalid (2 'O' fields) ~ASD~C12345~OF~OV <-- invalid (2 'O' fields) Thanks again for your help!! ------------------------------ John Wismar BSA - AllData Offline Products john.wismar@alldata.com

-----Original Message----- From: John Maddock [mailto:john_maddock@compuserve.com] Sent: Friday, May 30, 2003 3:43 AM To: Boost-Users@yahoogroups.com Subject: Re: [Boost-Users] Regex: matching either of 2 fields, in any order

...

I can see how I could do this in a loop to replace the different subfields. Is there another step I would need to take to guarantee that there is at most one of each type of subfield?

Well if you search for "C(\\d+)|O(\\w+)" it can only match one or the other can't it? Or am I missing something?

John.