How can I validate a string to only allow alphanumeric characters in it

Question

How can I validate a string using Regular Expressions to only allow alphanumeric characters in it    I don t want to allow for any spaces either

User · Answer

While there are many ways to skin this cat  I prefer to wrap such code into reusable extension methods that make it trivial to do going forward   When using extension methods  you can also avoid RegEx as it is slower than a direct character check   I like using the extensions in the Extensions cs NuGet package   It makes this check as simple as   Add the https   www nuget org packages Extensions cs package to your project  Add  quot using Extensions  quot  to the top of your code   quot smith23 quot  IsAlphaNumeric   will return True whereas  quot smith 23 quot  IsAlphaNumeric false  will return False   By default the  IsAlphaNumeric   method ignores spaces  but it can also be overridden as shown above   If you want to allow spaces such that  quot smith 23 quot  IsAlphaNumeric   will return True  simple default the arg  Every other check in the rest of the code is simply MyString IsAlphaNumeric

User · Answer

You could do it easily with an extension function rather than a regex      public static bool IsAlphaNum this string str        if  string IsNullOrEmpty str           return false       for  int i   0  i  lt  str Length  i                  if    char IsLetter str i     amp  amp     char IsNumber str i                  return false             return true      Per comment         public static bool IsAlphaNum this string str        if  string IsNullOrEmpty str           return false       return  str ToCharArray   All c   gt  Char IsLetter c     Char IsNumber c

User · Answer

Same answer as here   If you want a non-regex ASCII A-z 0-9 check  you cannot use char IsLetterOrDigit   as that includes other Unicode characters   What you can do is check the character code ranges     48 -  57 are numerics 65 -  90 are capital letters 97 -  122 are lower case letters   The following is a bit more verbose  but it s for ease of understanding rather than for code golf       public static bool IsAsciiAlphaNumeric this string str                if  string IsNullOrEmpty str                         return false                     for  int i   0  i  lt  str Length  i                          if  str i   lt  48     Numeric are 48 - gt  57                               return false                             if  str i   gt  57  amp  amp  str i   lt  65     Capitals are 65 - gt  90                               return false                             if  str i   gt  90  amp  amp  str i   lt  97     Lowers are 97 - gt  122                               return false                             if  str i   gt  122                                return false                                   return true

User · Answer

While I think the regex-based solution is probably the way I d go  I d be tempted to encapsulate this in a type   public class AlphaNumericString       public AlphaNumericString string s                Regex r   new Regex    a-zA-Z0-9               if  r IsMatch s                         value   s                                    else                       throw new ArgumentException  Only alphanumeric characters may be used                         private string value      static public implicit operator string AlphaNumericString s                return s value            Now  when you need a validated string  you can have the method signature require an AlphaNumericString  and know that if you get one  it is valid  apart from nulls    If someone attempts to pass in a non-validated string  it will generate a compiler error   You can get fancier and implement all of the equality operators  or an explicit cast to AlphaNumericString from plain ol  string  if you care

User · Answer

I advise to not depend on ready made and built in code in  NET framework   try to bring up new solution   this is what i do     public  bool isAlphaNumeric string N        bool YesNumeric   false      bool YesAlpha   false      bool BothStatus   false        for  int i   0  i  lt  N Length  i                  if  char IsLetter N i                 YesAlpha true           if  char IsNumber N i                YesNumeric   true             if  YesAlpha  true  amp  amp  YesNumeric  true                BothStatus   true            else               BothStatus   false            return BothStatus

User · Answer

I needed to check for A-Z  a-z  0-9  without a regex  even though the OP asks for regex    Blending various answers and comments here  and discussion from https   stackoverflow com a 9975693 292060  this tests for letter or digit  avoiding other language letters  and avoiding other numbers such as fraction characters   if   String IsNullOrEmpty testString       amp  amp  testString All c   gt  Char IsLetterOrDigit c   amp  amp   c  lt  128             Alphanumeric

User · Answer

In  NET 4 0 you can use LINQ    if  yourText All char IsLetterOrDigit           just letters and digits      yourText All will stop execute and return false the first time char IsLetterOrDigit reports false since the contract of All cannot be fulfilled then   Note  this answer do not strictly check alphanumerics  which typically is A-Z  a-z and 0-9   This answer allows local characters like          Update 2018-01-29  The syntax above only works when you use a single method that has a single argument of the correct type  in this case char    To use multiple conditions  you need to write like this   if  yourText All x   gt  char IsLetterOrDigit x     char IsWhiteSpace x

User · Answer

Based on cletus s answer you may create new extension   public static class StringExtensions               public static bool IsAlphaNumeric this string str                if  string IsNullOrEmpty str               return false           Regex r   new Regex    a-zA-Z0-9               return r IsMatch str

User · Answer

Use the following expression     a-zA-Z0-9      ie   using System Text RegularExpressions   Regex r   new Regex    a-zA-Z0-9       if  r IsMatch SomeString

User · Answer

w   will allow a-zA-Z0-9   Use   a-zA-Z0-9    to disallow underscore   Note that both of these require the string not to be empty  Using   instead of   allows empty strings

User · Answer

In order to check if the string is both a combination of letters and digits  you can re-write  jgauffin answer as follows using  NET 4 0 and LINQ   if  string IsNullOrWhiteSpace yourText   amp  amp   yourText Any char IsLetter   amp  amp  yourText Any char IsDigit           do something here

[c#] How can I validate a string to only allow alphanumeric characters in it?

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