Random String Generator Returning Same String

Question

I ve developed a random string generator but it s not behaving quite as I m hoping   My goal is to be able to run this twice and generate two distinct four character random strings   However  it just generates one four character random string twice   Here s the code and an example of its output   private string RandomString int size        StringBuilder builder   new StringBuilder        Random random   new Random        char ch      for  int i   0  i  lt  size  i                  ch   Convert ToChar Convert ToInt32 Math Floor 26   random NextDouble     65                              builder Append ch              return builder ToString          get 1st random string  string Rand1   RandomString 4       get 2nd random string  string Rand2   RandomString 4       create full rand string string docNum   Rand1    -    Rand2       and the output looks like this   UNTE-UNTE    but it should look something like this UNTE-FWNU  How can I ensure two distinctly random strings

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I think may be this is also acceptable and simple   Guid NewGuid   ToString

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Here is one more option   public System String GetRandomString System Int32 length        System Byte   seedBuffer   new System Byte 4       using  var rngCryptoServiceProvider   new System Security Cryptography RNGCryptoServiceProvider                  rngCryptoServiceProvider GetBytes seedBuffer           System String chars    abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789           System Random random   new System Random System BitConverter ToInt32 seedBuffer  0            return new System String Enumerable Repeat chars  length  Select s   gt  s random Next s Length    ToArray

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I found this to be more helpfull  since it is an extention  and it allows you to select the source of your code   static string     numbers    0123456789       letters    abcdefghijklmnopqrstvwxyz       lettersUp   letters ToUpper        codeAll   numbers   letters   lettersUp   static Random m rand   new Random     public static string GenerateCode this int size        return size GenerateCode CodeGeneratorType All      public static string GenerateCode this int size  CodeGeneratorType type        string source       if  type    CodeGeneratorType All                source   codeAll            else               StringBuilder sourceBuilder   new StringBuilder            if   type  amp  CodeGeneratorType Letters     CodeGeneratorType Numbers              sourceBuilder Append numbers           if   type  amp  CodeGeneratorType Letters     CodeGeneratorType Letters              sourceBuilder Append letters           if   type  amp  CodeGeneratorType Letters     CodeGeneratorType LettersUpperCase              sourceBuilder Append lettersUp            source   sourceBuilder ToString               return size GenerateCode source      public static string GenerateCode this int size  string source        StringBuilder code   new StringBuilder        int maxIndex   source Length-1      for  int i   0  i  lt  size  i                   code Append source Convert ToInt32 Math Round m rand NextDouble     maxIndex                 return code ToString       public enum CodeGeneratorType   Numbers   1  Letters   2  LettersUpperCase   4  All   16      Hope this helps

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The best solution is using the random number generator toghether with base64 conversion   public string GenRandString int length      byte   randBuffer   new byte length     RandomNumberGenerator Create   GetBytes randBuffer     return System Convert ToBase64String randBuffer  Remove length

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You should have one class-level Random object initiated once in the constructor and reused on each call  this continues the same sequence of pseudo-random numbers   The parameterless constructor already seeds the generator with Environment TickCount internally

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A very simple implementation that uses Path GetRandomFileName    using System IO     public static string RandomStr         string rStr   Path GetRandomFileName        rStr   rStr Replace  quot   quot    quot  quot       For Removing the       return rStr     Now just call RandomStr

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Another sample  tested in vs2013        Random R   new Random        public static string GetRandomString int Length                char   ArrRandomChar   new char Length           for  int i   0  i  lt  Length  i                ArrRandomChar i     char   a    R Next 0  26            return new string ArrRandomChar              string D   GetRandomString 12     Implemented by myself

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public static class StringHelpers       public static readonly Random rnd   new Random         public static readonly string EnglishAlphabet    abcdefghijklmnopqrstuvwxyz       public static readonly string RussianAlphabet                                             public static unsafe string GenerateRandomUTF8String int length  string alphabet                if  length  lt   0              return String Empty          if  string IsNullOrWhiteSpace alphabet               throw new ArgumentNullException  alphabet             byte   randomBytes   rnd NextBytes length            string s   new string alphabet 0   length            fixed  char  p   s                        for  int i   0  i  lt  s Length  i                                    p   i    alphabet randomBytes i    alphabet Length                                   return s             public static unsafe string GenerateRandomUTF8String int length  params UnicodeCategory   unicodeCategories                if  length  lt   0              return String Empty          if  unicodeCategories    null              throw new ArgumentNullException  unicodeCategories            if  unicodeCategories Length    0              return rnd NextString length            byte   randomBytes   rnd NextBytes length            string s   randomBytes ConvertToString            fixed  char  p   s                        for  int i   0  i  lt  s Length  i                                  while   unicodeCategories Contains char GetUnicodeCategory   p   i                           p   i      char   p   i                                   return s            You also will need this   public static class RandomExtensions       public static string NextString this Random rnd  int length                if  length  lt   0              return String Empty           return rnd NextBytes length  ConvertToString               public static byte   NextBytes this Random rnd  int length                if  length  lt   0              return new byte 0            byte   randomBytes   new byte length           rnd NextBytes randomBytes           return randomBytes            And this   public static class ByteArrayExtensions       public static string ConvertToString this byte   bytes                if  bytes Length  lt   0              return string Empty           char   chars   new char bytes Length   sizeof char            Buffer BlockCopy bytes  0  chars  0  bytes Length           return new string chars

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My RandomString   method to generate a random string   private static readonly Random  rand   new Random          lt summary gt      Generate a random string       lt  summary gt       lt param name  length  gt The length of random string  The minimum length is 3  lt  param gt       lt returns gt The random string  lt  returns gt  public string RandomString int length        length   Math Max length  3        byte   bytes   new byte length        rand NextBytes bytes       return Convert ToBase64String bytes  Substring 0  length

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As long as you are using Asp Net 2 0 or greater  you can also use the library call- System Web Security Membership GeneratePassword  however it will include special characters   To get 4 random characters with minimum of 0 special characters-  Membership GeneratePassword 4  0

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Hello you can use WordGenerator or LoremIpsumGenerator from MMLib RapidPrototyping nuget package   using MMLib RapidPrototyping Generators  public void WordGeneratorExample        WordGenerator generator   new WordGenerator       var randomWord   generator Next        Console WriteLine randomWord          Nuget site Codeplex project site

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A LINQ one-liner for good measure  assuming a private static Random Random      public static string RandomString int length        return new string Enumerable Range 0  length  Select     gt   char Random Next  a    z    ToArray

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This solution is an extension for a Random class   Usage  class Program       private static Random random   new Random          static void Main string   args                random NextString 10       cH  I fUWH0          random NextString 10       Cw amp N 27 EM          random NextString 10       0LZ nEJ  -          random NextString          kFmeget80LZ nEJ  -            Implementation  public static class RandomEx            lt summary gt          Generates random string of printable ASCII symbols of a given length          lt  summary gt           lt param name  r  gt instance of the Random class lt  param gt           lt param name  length  gt length of a random string lt  param gt           lt returns gt Random string of a given length lt  returns gt      public static string NextString this Random r  int length                var data   new byte length           for  int i   0  i  lt  data Length  i                             All ASCII symbols  printable and non-printable                data i     byte r Next 0  128                  Only printable ASCII             data i     byte r Next 32  127                     var encoding   new ASCIIEncoding            return encoding GetString data                   lt summary gt          Generates random string of printable ASCII symbols         with random length of 10 to 20 chars          lt  summary gt           lt param name  r  gt instance of the Random class lt  param gt           lt returns gt Random string of a random length between 10 and 20 chars lt  returns gt      public static string NextString this Random r                int length    r Next 10  21           return NextString r  length

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I added the option to choose the length using the Ranvir solution  public static string GenerateRandomString int length                              string randomString  string Empty               while  randomString Length  lt   length                                randomString   Path GetRandomFileName                    randomString  randomString Replace      string Empty                              return randomString Substring 0  length

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Just for people stopping by and what to have a random string in just one single line of code  int yourRandomStringLength   12    maximum  32 Guid NewGuid   ToString  N   Substring 0  yourRandomStringLength     PS  Please keep in mind that yourRandomStringLength cannot exceed 32 as Guid has max length of 32

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Yet another version of string generator  Simple  without fancy math and magic digits  But with some magic string which specifies allowed characters   Update  I made generator static  so it will not return same string when called multiple times  However this code is not thread-safe and is definitely not cryptographically secure    For password generation System Security Cryptography RNGCryptoServiceProvider should be used   private Random  random   new Random Environment TickCount    public string RandomString int length        string chars    0123456789abcdefghijklmnopqrstuvwxyz       StringBuilder builder   new StringBuilder length        for  int i   0  i  lt  length    i          builder Append chars  random Next chars Length          return builder ToString

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I created this method   It works great   public static string GeneratePassword int Lenght  int NonAlphaNumericChars                string allowedChars    abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNOPQRSTUVWXYZ0123456789           string allowedNonAlphaNum           amp     -         lt  gt                Random rd   new Random             if  NonAlphaNumericChars  gt  Lenght    Lenght  lt   0    NonAlphaNumericChars  lt  0              throw new ArgumentOutOfRangeException                 char   pass   new char Lenght               int   pos   new int Lenght               int i   0  j   0  temp   0              bool flag   false                 Random the position values of the pos array for the string Pass             while  i  lt  Lenght - 1                                j   0                  flag   false                  temp   rd Next 0  Lenght                   for  j   0  j  lt  Lenght  j                        if  temp    pos j                                                 flag   true                          j   Lenght                                         if   flag                                        pos i    temp                      i                                                   Random the AlphaNumericChars             for  i   0  i  lt  Lenght - NonAlphaNumericChars  i                    pass i    allowedChars rd Next 0  allowedChars Length                   Random the NonAlphaNumericChars             for  i   Lenght - NonAlphaNumericChars  i  lt  Lenght  i                    pass i    allowedNonAlphaNum rd Next 0  allowedNonAlphaNum Length                   Set the sorted array values by the pos array for the rigth posistion             char   sorted   new char Lenght               for  i   0  i  lt  Lenght  i                    sorted i    pass pos i                 string Pass   new String sorted                return Pass

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Actually  a good solution is to have a static method for the random number generator that is thread-safe and doesn t use locks   That way  multiple users accessing your web application at the same time don t get the same random strings   There are 3 examples here  http   blogs msdn com b pfxteam archive 2009 02 19 9434171 aspx  I d use the last one   public static class RandomGen3       private static RNGCryptoServiceProvider  global            new RNGCryptoServiceProvider         ThreadStatic      private static Random  local       public static int Next                 Random inst    local          if  inst    null                        byte   buffer   new byte 4                global GetBytes buffer                local   inst   new Random                  BitConverter ToInt32 buffer  0                      return inst Next              Then you can properly eliminate   Random random   new Random      And just call RandomGen3 Next    while your method can remain static

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For random string generator     region CREATE RANDOM STRING WORD         char   wrandom     A   B   C   D   E   F   G   H   I   J   K   L   M   N   O   P   R   S   T   U   V   X   W   Y   Z            Random random   new Random            string random string               int count   12    YOU WILL SPECIFY HOW MANY CHARACTER WILL BE GENERATE         for  int i   0  i  lt  count  i                           random string   random string   wrandom random Next 0  24   ToString                       MessageBox Show random string            endregion

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And here is another idea based on GUIDs  I ve used it for the Visual Studio performance test to generate random string contaning only alphanumeric characters   public string GenerateRandomString int stringLength        Random rnd   new Random        Guid guid      String randomString   string Empty       int numberOfGuidsRequired    int Math Ceiling  double stringLength   32d       for  int i   0  i  lt  numberOfGuidsRequired  i                  guid   Guid NewGuid            randomString    guid ToString   Replace  -                   return randomString Substring 0  stringLength

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If you have access to an Intel Secure Key compatible CPU  you can generate real random numbers and strings using these libraries  https   github com JebteK RdRand and https   www rdrand com   Just download the latest version from here  include Jebtek RdRand and add a using statement for it  Then  all you need to do is this   bool isAvailable   RdRandom GeneratorAvailable      Check to see if this is a compatible CPU string key   RdRandom GenerateKey 10     Generate 10 random characters   Plus  you also get these additional capabilities   string apiKey   RdRandom GenerateAPIKey      Generate 64 random characters  useful for API keys byte   b   RdRandom GenerateBytes 10     Generate an array of 10 random bytes uint i   RdRandom GenerateUnsignedInt     Generate a random unsigned int   If you don t have a compatible CPU to execute the code on  just use the RESTful services at rdrand com  With the RdRandom wrapper library included in your project  you would just need to do this  you get 1000 free calls when you signup    string ret   Randomizer GenerateKey  lt length gt     lt key gt       You can also generate random byte arrays and unsigned integers as follows   uint ret   Randomizer GenerateUInt   lt key gt     byte   ret   Randomizer GenerateBytes  lt length gt     lt key gt

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In my situation  the password must contain    At least one lower case  At least one upper case  At least one decimal  At least one special character    Here is my code       private string CreatePassword int len                string   valid      abcdefghijklmnopqrstuvwxyz    ABCDEFGHIJKLMNOPQRSTUVWXYZ    1234567890           amp                   RNGCryptoServiceProvider rndGen   new RNGCryptoServiceProvider             byte   random   new byte len           int   selected   new int len            do                       rndGen GetNonZeroBytes random                for  int i   0  i  lt  random Length  i                                  selected i    random i    4                                   while selected Distinct   Count      4            rndGen GetNonZeroBytes random            string res                for int i   0  i lt len  i                          res    valid selected i   random i    valid selected i   Length                     return res

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Combining the answer by  Pushcode  and the one using the seed for the random generator  I needed it to create a serie of pseudo-readable  words    private int RandomNumber int min  int max  int seed 0        Random random   new Random  int DateTime Now Ticks   seed       return random Next min  max

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You re instantiating the Random object inside your method   The Random object is seeded from the system clock  which means that if you call your method several times in quick succession it ll use the same seed each time  which means that it ll generate the same sequence of random numbers  which means that you ll get the same string   To solve the problem  move your Random instance outside of the method itself  and while you re at it you could get rid of that crazy sequence of calls to Convert and Floor and NextDouble    private readonly Random  rng   new Random    private const string  chars    ABCDEFGHIJKLMNOPQRSTUVWXYZ    private string RandomString int size        char   buffer   new char size        for  int i   0  i  lt  size  i                  buffer i     chars  rng Next  chars Length              return new string buffer

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Here is my modification of the currently accepted answer  which I believe it s a little faster and shorter   private static Random random   new Random     private string RandomString int size        StringBuilder builder   new StringBuilder size       for  int i   0  i  lt  size  i            builder Append  char random Next 0x41  0x5A        return builder ToString        Notice I didn t use all the multiplication  Math floor    Convert etc   EDIT  random Next 0x41  0x5A  can be changed to any range of Unicode characters

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This is my solution   private string RandomString int length        char   symbols                                   0    1    2    3    4    5    6    7    8    9                                a    b    c    d    e    f    g    h    i    j    k    l    m    n    o    p    q    r    s    t    u    v    w    x    y    z                                A    B    C    D    E    F    G    H    I    J    K    L    M    N    O    P    Q    R    S    T    U    V    W    X    Y    Z                                                               Stack lt byte gt  bytes   new Stack lt byte gt         string output   string Empty       for  int i   0  i  lt  length  i                  if  bytes Count    0                        bytes   new Stack lt byte gt  Guid NewGuid   ToByteArray                       byte pop   bytes Pop            output    symbols  int pop   symbols Length             return output        get 1st random string  string Rand1   RandomString 4       get 2nd random string  string Rand2   RandomString 4       create full rand string string docNum   Rand1    -    Rand2

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This is because each new instance of Random is generating the same numbers from being called so fast  Do not keep creating a new instance  just call next   and declare your random class outside of your method

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If you wanted to generate a string of Numbers and Characters for a strong password   private static Random random   new Random     private static string CreateTempPass int size                        var pass   new StringBuilder                for  var i 0  i  lt  size  i                                  var binary   random Next 0 2                   switch  binary                                        case 0                      var ch    Convert ToChar Convert ToInt32 Math Floor 26 random NextDouble     65                              pass Append ch                           break                      case 1                          var num   random Next 1  10                           pass Append num                           break                                              return pass ToString

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And  another version  I ve use this method for generating random pseudo stock symbols in testing   Random rand   new Random    Func lt char gt  randChar        gt   char rand Next 65  91      upper case ascii codes Func lt int string gt  randStr   null      randStr    x    gt   x gt 0    randStr --x  randChar            recursive   Usage   string str4   randStr 4     generates a random 4 char string string strx   randStr rand next 1 5       random string between 1-4 chars in length   You can redefine the randChar function for use with an  allowed  array of chars by position instead of ascii code   char   allowedchars     A   B   C   1   2   3    Func lt char gt  randChar        gt  allowedchars rand Next 0  allowedchars Length-1

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You re making the Random instance in the method  which causes it to return the same values when called in quick succession  I would do something like this   private static Random random   new Random  int DateTime Now Ticks    thanks to McAden private string RandomString int size                StringBuilder builder   new StringBuilder            char ch          for  int i   0  i  lt  size  i                          ch   Convert ToChar Convert ToInt32 Math Floor 26   random NextDouble     65                                  builder Append ch                      return builder ToString              get 1st random string  string Rand1   RandomString 4       get 2nd random string  string Rand2   RandomString 4       creat full rand string string docNum   Rand1    -    Rand2     modified version of your code

[c#] Random String Generator Returning Same String

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