Comparing arrays in C

Question

I am trying to compare two arrays with each other  I tried this code and got the following errors   static bool ArraysEqual Array a1  Array a2        if  a1    a2          return true       if  a1    null    a2    null          return false       if  a1 Length    a2 Length          return false       IList list1   a1  list2   a2    error CS0305  Using the generic type  System Collections Generic IList lt T gt   requires  1  type arguments     for  int i   0  i  lt  a1 Length  i                  if   Object Equals list1 i   list2 i      error CS0021  Cannot apply indexing with    to an expression of type  IList  x2              return false            return true      Why do I get that error  I went for a low-tech solution and did this which works fine  but I need to copy paste it several times for each type   static bool ArraysEqual byte   a1  byte   a2        if  a1    a2          return true       if  a1    null    a2    null          return false       if  a1 Length    a2 Length          return false       for  int i   0  i  lt  a1 Length  i                  if  a1 i     a2 i               return false            return true

User · Answer

Providing that you have LINQ available and don't care too much about performance, the easiest thing is the following:

var arraysAreEqual = Enumerable.SequenceEqual(a1, a2);

In fact, it's probably worth checking with Reflector or ILSpy what the SequenceEqual methods actually does, since it may well optimise for the special case of array values anyway!

User · Answer

I know this is an old topic  but I think it is still relevant  and would like to share an implementation of an array comparison method which I feel strikes the right balance between performance and elegance   static bool CollectionEquals lt T gt  ICollection lt T gt  a  ICollection lt T gt  b  IEqualityComparer lt T gt  comparer   null        return ReferenceEquals a  b     a    null  amp  amp  b    null  amp  amp  a Count    b Count  amp  amp  a SequenceEqual b  comparer       The idea here is to check for all of the early out conditions first  then fall back on SequenceEqual  It also avoids doing extra branching and instead relies on boolean short-circuit to avoid unecessary execution  I also feel it looks clean and is easy to understand   Also  by using ICollection for the parameters  it will work with more than just arrays

User · Answer

For  NET 4 0 and higher  you can compare elements in array or tuples using the StructuralComparisons type  object   a1      quot string quot   123  true    object   a2      quot string quot   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

User · Answer

Recommending SequenceEqual is ok  but thinking that it may ever be faster than usual for     loop is too naive   Here is the reflected code   public static bool SequenceEqual lt TSource gt  this IEnumerable lt TSource gt  first       IEnumerable lt TSource gt  second  IEqualityComparer lt TSource gt  comparer        if  comparer    null                comparer   EqualityComparer lt TSource gt  Default            if  first    null                throw Error ArgumentNull  first              if  second    null                throw Error ArgumentNull  second              using  IEnumerator lt TSource gt  enumerator   first GetEnumerator             using  IEnumerator lt TSource gt  enumerator2   second GetEnumerator                  while  enumerator MoveNext                          if   enumerator2 MoveNext       comparer Equals enumerator Current  enumerator2 Current                                 return false                                  if  enumerator2 MoveNext                          return false                      return true      As you can see it uses 2 enumerators and fires numerous method calls which seriously slow everything down  Also it doesn t check length at all  so in bad cases it can be ridiculously slower   Compare moving two iterators with beautiful  if  a1 i     a2 i     and you will know what I mean about performance   It can be used in cases where performance is really not so critical  maybe in unit test code  or in cases of some short list in rarely called methods

User · Answer

SequenceEqual can be faster  Namely in the case where almost all of the time  both arrays have indeed the same length and are not the same object   It s still not the same functionality as the OP s function  as it won t silently compare null values

User · Answer

Why do i get that error   - probably  you don t have  using System Collections   at the top of the file - only  using System Collections Generic   - however  generics are probably safer - see below   static bool ArraysEqual lt T gt  T   a1  T   a2        if  ReferenceEquals a1 a2           return true       if  a1    null    a2    null          return false       if  a1 Length    a2 Length          return false       EqualityComparer lt T gt  comparer   EqualityComparer lt T gt  Default      for  int i   0  i  lt  a1 Length  i                  if   comparer Equals a1 i   a2 i    return false            return true

[c#] Comparing arrays in C#

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