Re: Finding formatting items in a string

Hello Jack,

Hi there,

Given a standard .NET string, does anyone know what the regular
expression would be to locate each (optional) formatting item in the
string (or more likely does anyone have a link that will show me
this). For instance, given the following simple string:

"My phone number is {0} and my SSN is {1}"

I want to enumerate (or create a collection of) all formatting items
in the string which would be "{0}" and "{1}" in this (trivial)
example. The regular expression itself should handle all legal cases
of course (as described under "composite formatting" in MSDN - see
here: http://msdn2.microsoft.com/en-us/library/txafckwd.aspx). Any
help would be appreciated. Thanks.


The following expression will take care of most you want:

(?<!([^\{]|^)\{(\{{2})*)\{[0-9]+(,[-]?[0-9]+)?(:[^\}]+)?\}(?!\}(\{{2})*([^\}]|$))

I'll try to explain what it does:

(?<!([^\{]|^)\{(\{{2})*)
This part sees if we're dealing with an even number of opening {. In that case all are escaped and should therefore be ignored.
Due to the fact that there is no easy way to check for off or even numbers I've done it as follows: - first make sure we're either at the beginning of a line or that we match a character that is no {. That way we're sure where we're startign to count.
- Now chop off the first {, followed by any group of 2 extra {'s.

\{
- If that still leaves us with one {, then we're in business.

[0-9]+
- Now accept the numbered part. I've made it pretty simple here, any number will so.

(,[-]?[0-9]+)?
- Now accept the optional alignment. I think you could write the [-] as [+-], but I'm not sure from the top of my head that a plus is allowed for the alignment. I guess it is though.

(:[^\}]+)?
- Accept almost anything as optional formatting mask. As you can specify the formatting mask for each and every tipe differently based on the TypeFormatter, I guess there's no use in limiting the possible formats any way.
- So chop off everything that's not a closing }

\}
- Pick off the closing }

(?!\}(\{{2})*([^\}]|$))
- But only if it's followed by no or an odd number of closing }'s. This used the same logic as above.

You could make the regex more specific, but I guess this should get you started.

Also note that I haven't taken any whitespace into account, as I haven't had time to experiment where you would be allowed to add whitespace and where not.

If you still have any questions on how to improve or further limit the expression, feel free to ask.

--
Jesse Houwing
jesse.houwing at sogeti.nl


.

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