"C #" regular Expressions match Chinese, English letters and numbers and _ Writing! and control the length of __ regular expressions

using System.Text.RegularExpressions;

Match Chinese: [\u4e00-\u9fa5]

English letter: [A-za-z]

Number: [0-9]

Match Chinese, English letters and numbers and _:
^[\u4e00-\u9fa5_a-za-z0-9]+$

At the same time determine the input length:
[\u4e00-\u9fa5_a-za-z0-9_] {4,10}

^[\w\u4e00-\u9fa5\uf900-\ufa2d]*$1, a regular expression containing only Chinese characters, numbers, letters, underscores cannot begin and end with an underscore:
^(?! _)(?!. *?_$) [a-za-z0-9_\u4e00-\u9fa5]+$ of which:
^ matches where the string begins
(?! _) cannot start with _
(?!. *?_$) cannot end with _
[a-za-z0-9_\u4e00-\u9fa5]+ at least one Chinese character, number, letter, underline
$ matches where the string ends

Put @ in front of the program, or you need to escape @ ^ (?! _)(?!. *?_$) [a-za-z0-9_\u4e00-\u9fa5]+$]
(or: @ "^" ^ (?!) _) \w* (?
2, only contain Chinese characters, numbers, letters, underline, the underline position is not limited:
^[a-za-z0-9_\u4e00-\u9fa5]+$

3. A string of numbers, 26 English letters, or underscores
^\w+$

4.2~4 a Chinese character
@ "^[\u4e00-\u9fa5]{2,4}$";

5,
^[\w-]+ (\.[ \w-]+) *@[\w-]+ (\.[ \w-]+) +$

Used: (ABC) + to analyze: XYZAbcAbcAbcXYZAbcAb

Xyz ABCABCABCXyz ABCAb6,
[^\u4e00-\u9fa50-9a-za-z_]
34555#5 '-->34555 #5 '

[\u4e00-\u9fa50-9a-za-z_] eiieng_89_--->eiieng_89_
_';' eiieng_88&*9_-->_ '; ' Eiieng_88&*9_
_';' eiieng_88_&*9_-->_ '; ' Eiieng_88_&*9_

public bool Regexname (string str)
{
BOOL Flag=regex.ismatch (str,@ "^[a-za-z0-9_\u4e00-\u9fa5]+$");
return flag;
}

Regex reg=new Regex ("^[a-za-z_0-9]+$");
if (Reg. IsMatch (s))
{
\ Compliance Rules
}
Else
{
\ \ There are illegal characters
}

no longer than 7 characters, or 14 bytes (digits, letters and underscores) regular Expressions
^[\u4e00-\u9fa5]{1,7}$|^[\da-za-z_]{14}$