Here we will see how to use regular expression in .NET to validate input.
Regular Expressions Elements:
- . Character except a newline character(\n)
- \d Any decimal digit
- \D Any nondigit
- \s Any white-space character
- \S Any Non-white-space charater
- \w Any word character
- \W Any nonword character
- ^ Beginning of string or line
- \A Beginning of string
- $ End of string or line
- \z End of string
- | Matches one of the expressions seprated by the vertical bar; example eee|ttt will match one of eee or ttt (tracing left to right)
- [abc] Match with one of the characters; example [rghy] will match r, g,h or c not any other character.
- [^abc] Match with any of character except in list; example [ghj] will match all character except g,h or k.
- [a-z] Match any character within specified range; example [a - c] will match a, b or c.
- ( ) Subexpression treated as a single element by regular expression elements described in this table.
- ? Match one or zero occurrences of the previous character or subexpression; example a?b will match a or ab not aab.
- * Match zero or more occurences of the previous character or subexpression; example a*b will match b, ab, aab and so on.
- + Match one or more occurences of the previous character or subexpression; example a+b will match ab, aab and so on but not b.
- {n} Match exactly n occurrences of the preceding character;example a{2} will match only aa.
- {n,} Match minimum n occurrences of the preceding character;example a{2,} will match only aa,aaa and so on.
- {n,m} Match minimum n and maximum n occurrences of the preceding character;example a{2, 4} will match aa, aaa, aaaa but not aaaaa.
Example Regular Expression :
- Numeric input: ^\d+$ Consists of one or more decimal digits ; example 9 or 9873455.
- Credit Card Number: ^\d{4}-?\d{4}-?\d{4}-?\d{4}$
- Email Address: ^[\w-]+@([\w-]+\.)+[\w-]+$
Using in C#:
- Namespace of regular expressions : using System.Text.RegularExpressions;
- Class : Regex;
- Object : Regex reg = new Regex(string expression);
- Match Function : reg.IsMatch(string Input) returns bool value.
True Input is in correct format[YaaaHooooo].
False Input is in wrong format[Oh No].