my head is spinning with regex

[Daniel Billingsley]

First, if MSFT is listening I'll say IMO the MSDN material is sorely lacking
in this area... it's just a whole bunch of information thrown at you and
you're left to yourself as to organizing it in your head. Typical learning
starts with basics and progresses through increasingly complex information -
I think given the inherent confusion-inducing ability of regex that kind of
documentation would be very valuable.

But anyway, I'm trying to write a regex that will parse a line of code from
a .cs file into the code and comments portions if there is a // somewhere in
the line. I realize this may need to be more complex down the road to
handle special occurrences of // other than in a comment (like in a string
literal), but I'm trying to start with the basics. So I have...

Regex regex = new Regex(@"(?<code >.+)//(?<comments>.+) ",
RegexOptions.Co mpiled);
regexMatch = regex.Match(ori ginal);
if (regexMatch.Suc cess)
{
code = regexMatch.Resu lt("${code}");
comments = regexMatch.Resu lt("${comments} ");
}

This works fine on
// A basic comment line
or
a = b; // code line with comment afterward

but on the line
/// <summary>

I end up with
code = "/"
comment = " <summary>"

I'm not understanding why the "//" in my regex seems to match the "last"
occurrence of the pattern and "skips" the match on the first two slashes of
the three. I thought by definition the first occurrence would be matched.
Indeed, if my original line is "//// something" I end up with "//" and "
something".

Who can clarify this for me? And who can point me to a *good* resource for
regex edumucation?

[Brian Davis]

Try this instead:

(?<code>.*?)//(?<comments>.*)
First of all, changing the +s to *s will allow the regex to match even if
there are no characters before/after the "//". Also, adding the "?" after
the code portion will allow it to match the first occurrence of "//" as
opposed to the last. The ".*" is greedy, so it will consume all that it can
and only give up characters as it needs to in order to match the rest of the
expression. Using the ".*?" makes it lazy, so that it matches only what it
must match in order to continue matching the rest of the expression.
Brian Davis
www.knowdotnet.com


"Daniel Billingsley" <db**********@N O.durcon.SPAAMM .com> wrote in message
news:OA******** ********@tk2msf tngp13.phx.gbl. ..

First, if MSFT is listening I'll say IMO the MSDN material is sorely lacking in this area... it's just a whole bunch of information thrown at you and
you're left to yourself as to organizing it in your head. Typical learning starts with basics and progresses through increasingly complex information - I think given the inherent confusion-inducing ability of regex that kind of documentation would be very valuable.

But anyway, I'm trying to write a regex that will parse a line of code from a .cs file into the code and comments portions if there is a // somewhere in the line. I realize this may need to be more complex down the road to
handle special occurrences of // other than in a comment (like in a string
literal), but I'm trying to start with the basics. So I have...

Regex regex = new Regex(@"(?<code >.+)//(?<comments>.+) ",
RegexOptions.Co mpiled);
regexMatch = regex.Match(ori ginal);
if (regexMatch.Suc cess)
{
code = regexMatch.Resu lt("${code}");
comments = regexMatch.Resu lt("${comments} ");
}

This works fine on
// A basic comment line
or
a = b; // code line with comment afterward

but on the line
/// <summary>

I end up with
code = "/"
comment = " <summary>"

I'm not understanding why the "//" in my regex seems to match the "last"
occurrence of the pattern and "skips" the match on the first two slashes of the three. I thought by definition the first occurrence would be matched.
Indeed, if my original line is "//// something" I end up with "//" and "
something".

Who can clarify this for me? And who can point me to a *good* resource for regex edumucation?

[Daniel Billingsley]

Thanks Brian, the *? did it. My error there seems like a DOH! moment now.

Also, I found a cool tool that let's you experiment with regex realtime
http://www.weitz.de/regex-coach/

It has a "step" capability that let's you watch the regex work it's magic
step by step. Indeed, just like you describe, stepping through my original
..+ expression the first .+ gobbles up the whole input string (greedy) and
then only gives back what is necessary to match the //, starting at the END
of the string (so it can give up as little as possible). Hence it "gave up"
the // at the end of /// and not the beginning. Using the *? it starts at
the beginning of the input string and only eats up characters until it
reaches the // match, which is of course what I wanted. Very interesting to
see this behavior played out step by step.
"Brian Davis" <@> wrote in message
news:O7******** ********@TK2MSF TNGP12.phx.gbl. ..

Try this instead:

(?<code>.*?)//(?<comments>.*)
First of all, changing the +s to *s will allow the regex to match even if
there are no characters before/after the "//". Also, adding the "?" after
the code portion will allow it to match the first occurrence of "//" as
opposed to the last. The ".*" is greedy, so it will consume all that it can and only give up characters as it needs to in order to match the rest of the expression. Using the ".*?" makes it lazy, so that it matches only what it must match in order to continue matching the rest of the expression.
Brian Davis
www.knowdotnet.com


"Daniel Billingsley" <db**********@N O.durcon.SPAAMM .com> wrote in message
news:OA******** ********@tk2msf tngp13.phx.gbl. ..

First, if MSFT is listening I'll say IMO the MSDN material is sorely lacking

in this area... it's just a whole bunch of information thrown at you and
you're left to yourself as to organizing it in your head. Typical

learning

starts with basics and progresses through increasingly complex

information -

I think given the inherent confusion-inducing ability of regex that kind

of

documentation would be very valuable.

But anyway, I'm trying to write a regex that will parse a line of code

from

a .cs file into the code and comments portions if there is a // somewhere in

the line. I realize this may need to be more complex down the road to
handle special occurrences of // other than in a comment (like in a

string literal), but I'm trying to start with the basics. So I have...

Regex regex = new Regex(@"(?<code >.+)//(?<comments>.+) ",
RegexOptions.Co mpiled);
regexMatch = regex.Match(ori ginal);
if (regexMatch.Suc cess)
{
code = regexMatch.Resu lt("${code}");
comments = regexMatch.Resu lt("${comments} ");
}

This works fine on
// A basic comment line
or
a = b; // code line with comment afterward

but on the line
/// <summary>

I end up with
code = "/"
comment = " <summary>"

I'm not understanding why the "//" in my regex seems to match the "last"
occurrence of the pattern and "skips" the match on the first two slashes

of

the three. I thought by definition the first occurrence would be matched. Indeed, if my original line is "//// something" I end up with "//" and "
something".

Who can clarify this for me? And who can point me to a *good* resource

for

regex edumucation?