What is a quick way to force CRLF in C NET

Question

How would you normalize all new-line sequences in a string to one type   I m looking to make them all CRLF for the purpose of email  MIME documents    Ideally this would be wrapped in a static method  executing very quickly  and not using regular expressions  since the variances of line breaks  carriage returns  etc  are limited    Perhaps there s even a BCL method I ve overlooked   ASSUMPTION  After giving this a bit more thought  I think it s a safe assumption to say that CR s are either stand-alone or part of the CRLF sequence   That is  if you see CRLF then you know all CR s can be removed   Otherwise it s difficult to tell how many lines should come out of something like   r n n r

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Simple variant   Regex Replace input     r n  r  n     r n     For better performance   static Regex newline pattern   new Regex    r n  r  n   RegexOptions Compiled             newline pattern Replace input    r n

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input Replace   r n     n   Replace   r     n   Replace   n     r n     This will work if the input contains only one type of line breaks - either CR  or LF  or CR LF

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This is a quick way to do that  I mean   It does not use an expensive regex function  It also does not use multiple replacement functions that each individually did loop over the data with several checks  allocations  etc   So the search is done directly in one for loop  For the number of times that the capacity of the result array has to be increased  a loop is also used within the Array Copy function  That are all the loops  In some cases  a larger page size might be more efficient   public static string NormalizeNewLine this string val        if  string IsNullOrEmpty val           return val       const int page   6      int a   page      int j   0      int len   val Length      char   res   new char len        for  int i   0  i  lt  len  i                  char ch   val i            if  ch      r                         int ni   i   1              if  ni  lt  len  amp  amp  val ni       n                                 res j        r                   res j        n                   i                              else                               if  a    page     Ensure capacity                                       char   nres   new char res Length   page                       Array Copy res  0  nres  0  res Length                       res   nres                      a   0                                     res j        r                   res j        n                   a                                    else if  ch      n                         int ni   i   1              if  ni  lt  len  amp  amp  val ni       r                                 res j        r                   res j        n                   i                              else                               if  a    page     Ensure capacity                                       char   nres   new char res Length   page                       Array Copy res  0  nres  0  res Length                       res   nres                      a   0                                     res j        r                   res j        n                   a                                    else                       res j      ch                       return new string res  0  j       I now that   n r  is not actually used on basic platforms  But who would use two types of linebreaks in succession to indicate two linebreaks   If you want to know that  then you need to take a look before to know if the  n and  r both are used separately in the same document

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string nonNormalized     r n n r    string normalized   nonNormalized Replace   r     n   Replace   n     r n

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Environment NewLine  A string containing  quot  r n quot  for non-Unix platforms  or a string containing  quot  n quot  for Unix platforms

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It depends on exactly what the requirements are  In particular  how do you want to handle   r  on its own  Should that count as a line break or not  As an example  how should  a n rb  be treated  Is that one very odd line break  one   n  break and then a rogue   r   or two separate linebreaks  If   r  and   n  can both be linebreaks on their own  why should   r n  not be treated as two linebreaks   Here s some code which I suspect is reasonably efficient   using System  using System Text   class LineBreaks           static void Main                 Test  a nb            Test  a nb r nc            Test  a r nb r nc            Test  a rb nc            Test  a r            Test  a n            Test  a r n               static void Test string input                string normalized   NormalizeLineBreaks input           string debug   normalized Replace   r      r                                     Replace   n      n            Console WriteLine debug              static string NormalizeLineBreaks string input                   Allow 10  as a rough guess of how much the string may grow             If we re wrong we ll either waste space or have extra copies -            it will still work         StringBuilder builder   new StringBuilder  int   input Length   1 1             bool lastWasCR   false           foreach  char c in input                        if  lastWasCR                                lastWasCR   false                  if  c      n                                         continue     Already written  r n                                             switch  c                                case   r                       builder Append   r n                        lastWasCR   true                      break                  case   n                       builder Append   r n                        break                  default                      builder Append c                       break                                  return builder ToString

[c#] What is a quick way to force CRLF in C# / .NET?

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