Easiest way to compare arrays in C

Question

In Java  Arrays equals   allows to easily compare the content of two basic arrays  overloads are available for all the basic types    Is there such a thing in C   Is there any  magic  way of comparing the content of two arrays in C

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This LINQ solution works  not sure how it compares in performance to SequenceEquals  But it handles different array lengths and the  All will exit on the first item that is not equal without iterating through the whole array   private static bool arraysEqual lt T gt  IList lt T gt  arr1  IList lt T gt  arr2            gt              ReferenceEquals arr1  arr2                       arr1    null  amp  amp  arr2    null  amp  amp                  arr1 Count    arr2 Count  amp  amp                  arr1 Select  a  i    gt  arr2 i  Equals a   All i   gt  i

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I was looking to determine if two sets had equivalent contents  in any order   That meant that  for each element in set A there were equal numbers of elements with that value in both sets   I wanted to account for duplicates  so  1 2 2 3  and  1 2 3 3  should not be considered  quot the same quot    This is what I came up with  note that IsNullOrEmpty is another static extension method that returns true if the enumerable is null or has 0 elements       public static bool HasSameContentsAs lt T gt  this IEnumerable lt T gt  source  IEnumerable lt T gt  target           where T   IComparable                 If our source is null or empty  then it s just a matter of whether or not the target is too         if  source IsNullOrEmpty                return target IsNullOrEmpty               Otherwise  if the target is null emtpy  they can t be equal         if  target IsNullOrEmpty                return false             Neither is null or empty  so we ll compare contents   To account for multiples of            a given value  ex  1 2 2 3 and 1 1 2 3 are not equal  we ll group the first set         foreach  var group in source GroupBy s   gt  s                           If there are a different number of elements in the target set  they don t match             if  target Count t   gt  t Equals group Key      group Count                    return false                       If we got this far  they have the same contents         return true

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int   a     2  1  3  4  5  2             int   b     2  1  3  4  5  2             bool ans   true           if a Length    b Length                        ans   false                    else                       for  int i   0  i  lt  a Length  i                                  if  a i     b i                                         ans   false                                                     string str    quot  quot            if ans    true                        str    quot Two Arrays are Equal quot                      if  ans    false                        str    quot Two Arrays are not Equal quot                       --------------Or You can write One line of Code-------------          var ArrayEquals   a SequenceEqual b        returns true

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SequenceEqual will only return true if two conditions or met    They contain the same elements   The elements are in the same order    If you only want to check if they contain the same elements regardless of their order and your problem is of the type     Does values2 contain all the values contained in values1    you can use LINQ extension method Enumerable Except and then check if the result has any value  Here s an example  int   values1     1  2  3  4    int   values2     1  2  5    var result   values1 Except values2   if result Count    0         They are the same   else         They are different     And also by using this you get the different items as well automatically  Two birds with one stone   Keep in mind  if you execute your code like this   var result   values2 Except values1     you will get different results   In my case I have a local copy of an array and want to check if anything has been removed from the original array so I use this method

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You can use Enumerable Intersect  int   array1   new int     1  2  3  4 5          array2   new int    7 8    if  array1 Intersect array2  Any        Console WriteLine  quot matched quot    else     Console WriteLine  quot not matched quot

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If you would like to handle null inputs gracefully  and ignore the order of items  try the following solution  static class Extensions       public static bool ItemsEqual lt TSource gt  this TSource   array1  TSource   array2                if  array1    null  amp  amp  array2    null              return true          if  array1    null    array2    null              return false          if  array1 Count      array2 Count                return false          return  array1 Except array2  Any    amp  amp   array2 Except array1  Any             The test code looks like  public static void Main         int   a1   new int     1  2  3        int   a2   new int     3  2  1        int   a3   new int     1  3        Console WriteLine a1 ItemsEqual a2       Output  True      Console WriteLine a2 ItemsEqual a3       Output  False      Console WriteLine a3 ItemsEqual a2       Output  False          int   a4   new int     1  1        int   a5   new int     1  2        Console WriteLine a4 ItemsEqual a5       Output  False      Console WriteLine a5 ItemsEqual a4       Output  False           int   a6   null      int   a7   null      int   a8   new int 0        Console WriteLine a6 ItemsEqual a7       Output  True  No Exception      Console WriteLine a8 ItemsEqual a6       Output  False  No Exception      Console WriteLine a7 ItemsEqual a8       Output  False  No Exception

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I did this in visual studios and it worked perfectly  comparing arrays index by index with short this code   private void compareButton Click object sender  EventArgs e                        int   answer     1  3  4  6  8  9  5  4  0  6                int   exam     1  2  3  6  8  9  5  4  0  7                 int correctAnswers   0              int wrongAnswers   0               for  int index   0  index  lt  answer Length  index                                  if  answer index     exam index                                         correctAnswers    1                                    else                                       wrongAnswers    1                                               outputLabel Text     The matching numbers are     correctAnswers                     n     The non matching numbers are     wrongAnswers               the output will be  The matching numbers are 7                     The non matching numbers are 3

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For unit tests  you can use CollectionAssert AreEqual instead of Assert AreEqual    It is probably the easiest way

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For some applications may be better   string Join      arr1     string Join      arr2

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Use Enumerable SequenceEqual in LINQ   int   arr1   new int     1 2 3   int   arr2   new int     3 2 1     Console WriteLine arr1 SequenceEqual arr2       false Console WriteLine arr1 Reverse   SequenceEqual arr2       true

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elementwise compare   what about   public void Linq78a      int   numbers1     5  4  1  3  9  8  6  7  2  0     int   numbers     5  4  1  3  9  8  6  7  2  0     bool bb   numbers Zip numbers1   a  b    gt   a    b   Any p   gt   p    if   bb  Console WriteLine  Lists are equal  bb        else Console WriteLine  Lists are not equal  bb         Replace the  a  b  condition by anything you d like to compare in a and b    this combines two examples from MSDN developer Linq samples

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If you don t want to compare the order but you do want to compare the count of each item  including handling null values  then I ve written an extension method for this  It gives for example the following results  new int        IgnoreOrderComparison new int                                     true new int     1   IgnoreOrderComparison new int                                    false new int       IgnoreOrderComparison new int   1                                  false new int     1   IgnoreOrderComparison new int   1                                true new int     1  2   IgnoreOrderComparison new int   2  1                          true new int     1  2  null   IgnoreOrderComparison new int   2  1                    false new int     1  2  null   IgnoreOrderComparison new int   null  2  1              true new int     1  2  null  null   IgnoreOrderComparison new int   null  2  1        false new int     2   IgnoreOrderComparison new int   2  2                             false new int     2  2   IgnoreOrderComparison new int   2  2                          true  Here is the code  public static class ArrayComparisonExtensions       public static bool IgnoreOrderComparison lt TSource gt  this IEnumerable lt TSource gt  first  IEnumerable lt TSource gt  second    gt          IgnoreOrderComparison first  second  EqualityComparer lt TSource gt  Default        public static bool IgnoreOrderComparison lt TSource gt  this IEnumerable lt TSource gt  first  IEnumerable lt TSource gt  second  IEqualityComparer lt TSource gt  comparer                var a   ToDictionary first  out var firstNullCount           var b   ToDictionary second  out var secondNullCount            if  a Count    b Count              return false           if  firstNullCount    secondNullCount              return false           foreach  var item in a                        if  b TryGetValue item Key  out var count   amp  amp  item Value    count                  continue              return false                      return true           Dictionary lt TSource  int gt  ToDictionary IEnumerable lt TSource gt  items  out int nullCount                        nullCount   0              var result   new Dictionary lt TSource  int gt  comparer               foreach  var item in items                                if  item is null                      nullCount                    else if  result TryGetValue item  out var count                       result item    count   1                  else                     result item    1                             return result                     It only enumerates each enumerable once  but it does create a dictionary for each enumerable and iterates those once too  I d be interested in ways to improve this

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You could use Enumerable SequenceEqual   This works for any IEnumerable lt T gt   not just arrays

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For  NET 4 0 and higher you can compare elements in array or tuples via using StructuralComparisons type   object   a1      string   123  true    object   a2      string   123  true     Console WriteLine  a1    a2             False  because arrays is reference types  Console WriteLine  a1 Equals  a2        False  because arrays is reference types   IStructuralEquatable se1   a1    Next returns True Console WriteLine  se1 Equals  a2  StructuralComparisons StructuralEqualityComparer

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Also for arrays  and tuples  you can use new interfaces from  NET 4 0  IStructuralComparable and IStructuralEquatable  Using them you can not only check equality of arrays but also compare them   static class StructuralExtensions       public static bool StructuralEquals lt T gt  this T a  T b          where T   IStructuralEquatable               return a Equals b  StructuralComparisons StructuralEqualityComparer              public static int StructuralCompare lt T gt  this T a  T b          where T   IStructuralComparable               return a CompareTo b  StructuralComparisons StructuralComparer                  var a   new     1  2  3        var b   new     1  2  3        Console WriteLine a Equals b       False     Console WriteLine a StructuralEquals b       True         var a   new     1  3  3        var b   new     1  2  3        Console WriteLine a StructuralCompare b       1

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Assuming array equality means both arrays have equal elements at equal indexes  there is the SequenceEqual answer and the IStructuralEquatable answer  But both have drawbacks  performance wise  SequenceEqual current implementation will not shortcut when the arrays have different lengths  and so it may enumerate one of them entirely  comparing each of its elements  IStructuralEquatable is not generic and may cause boxing of each compared value  Moreover it is not very straightforward to use and already calls for coding some helper methods hiding it away  It may be better  performance wise  to use something like  bool ArrayEquals lt T gt  T   first  T   second        if  first    second          return true      if  first    null    second    null          return false      if  first Length    second Length          return false      for  var i   0  i  lt  first Length  i                  if   first i  Equals second i                return false            return true     But of course  that is not either some  quot magic way quot  of checking array equality  So currently  no  there is not really an equivalent to Java Arrays equals   in  Net

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