Regular expression. After searching for a long time on the Internet, there is no answer! Ask for advice online

japanshit

For example a string:
aadfgsdg take aadfgsdg
 aajsa; kfjn take aajsa; kfjn
(adfasf) aa take aa
asfdasfaaaaas323 cannot get value
afffasfdaaakjasdfa cannot get value
adfafffdaa ........ take aa ........
Claim
1) Take the content starting from aa.
2) There may not be aa after the string, if there is, it cannot be a
3) There may not be aa before the string, if it cannot be a

japanshit

Mostly unsolved!

mohicanhj

Do not quite understand the purpose of the landlord, but according to your requirements, use the following test, the test passes

string yourStr = textBox1.Text;
Match m = Regex.Match (yourStr, ". *? (? <! A) (aa (?! A). *)");
textBox2.Text = m.Groups [1] .Value; //Groups[1].Value is the content to be extracted

cqgang

^ (? = [^ a] *) aa [^ a] * $

cqgang

[^ a] means the inverse character set of a
aa [^ a] * means that there may be non-a characters after aa
(? = [^ a] *) means looking forward, there may be non-a characters in front but not included in the match
^ Start sign
$ End mark

kalian2000

I wrote a troublesome ..

Regex rx = new Regex (@ "^ ([\s\S] * [^ a])? (Aa ([^ a] [\s\S] *)?) $");
Match m = rx.Match (str);
if (m.Success)
{
     Console.WriteLine (m.Groups [2] .Value);
}

kalian2000

test:

Regex rx = new Regex (@ "^ ([\s\S] * [^ a])? (Aa ([^ a] [\s\S] *)?) $");

            string str = Console.ReadLine ();
            while (str! = "exit")
            {
                Match m = rx.Match (str);
                if (m.Success)
                {
                    Console.WriteLine (m.Groups [2] .Value);
                }
                str = Console.ReadLine ();
            }

lbningmeng

string str = "asfdaasfas323";
string str2 = System.Text.RegularExpressions.Regex.Replace (str, "^ aa |. *? [^ a] aa (?! a)", "$");
if (str.Equals (str2))
{
Response.Write ("Empty");
}
else
{
Response.Write (str2);
}
Haha, it's difficult, but I was blinded by me and the test passed!

linhanerror

string str = "adfafffdaa ........";
Regex reg = new Regex ("((? <= [^ A]) | ^) aa (([^ a]. *) | $)");
str = reg.Match (a) .Value;
// This should be fine

蜘蛛蝎

^ [^ a] *? (aa (?! a). *) | [^ a] (aa [^ a] *?) $
Note: When taking values, the values ​​of $ 1 and $ 2 can be taken together. One must be empty and the other a positive solution.

aadfgsdg takes aadfgsdg (take $ 1)
 aajsa; kfjn take aajsa; kfjn (take $ 1)
(adfasf) aa take aa (take $ 2)
asfdasfaaaaas323 cannot get the value
afffasfdaaakjasdfa cannot get the value
adfafffdaa ........ Take aa ........ (take $ 2)

C # find matches:
using System.Text.RegularExpressions;

// Regular expression object
Regex re = new Regex (@ "^ [^ a] *? (Aa (?! A). *) | [^ A] (aa [^ a] *?) $");

// Match object
Match m = re.Match ("your string");

// found
if (m.Success)
{
    // turn up
}
else
{
    // Not found
}