Comparing arrays for equality in C

Question

Can someone please explain to me why the output from the following code is saying that arrays are not equal   int main          int iar1      1 2 3 4 5       int iar2      1 2 3 4 5        if  iar1    iar2          cout  lt  lt   Arrays are equal        else         cout  lt  lt   Arrays are not equal         return 0

User · Answer

Right  In most  if not all implementations of C  the array identifier can be implicitly casted to a pointer to the first element  i e  the first element s address   What you re doing here is comparing those addresses  which is obviously wrong   Instead  you need to iterate over both arrays  checking each element against each other  If you get to the end of both without a failure  they re equal

User · Answer

Since nobody mentioned it yet  you can compare arrays with the std  equal algorithm   int iar1      1 2 3 4 5   int iar2      1 2 3 4 5    if  std  equal std  begin iar1   std  end iar1   std  begin iar2        cout  lt  lt   Arrays are equal    else     cout  lt  lt   Arrays are not equal      You need to include  lt algorithm gt  and  lt iterator gt   If you don t use C  11 yet  you can write   if  std  equal iar1  iar1   sizeof iar1   sizeof  iar1  iar2

User · Answer

Array is not a primitive type  and the arrays belong to different addresses in the C   memory

User · Answer

You re not comparing the contents of the arrays  you re comparing the addresses of the arrays  Since they re two separate arrays  they have different addresses   Avoid this problem by using higher-level containers  such as std  vector  std  deque  or std  array

User · Answer

Both store memory addresses to the first elements of two different arrays  These addresses can t be equal hence the output

User · Answer

When we use an array  we are really using a pointer to the first element in the array  Hence  this condition if  iar1    iar2   actually compares two addresses  Those pointers do not address the same object

User · Answer

Nobody mentions memcmp  This is also a good choice      memcmp example     include  lt stdio h gt   include  lt string h gt   int main        char buffer1      DWgaOtP12df0     char buffer2      DWGAOTP12DF0      int n     n memcmp   buffer1  buffer2  sizeof buffer1        if  n gt 0  printf     s  is greater than   s   n  buffer1 buffer2     else if  n lt 0  printf     s  is less than   s   n  buffer1 buffer2     else printf     s  is the same as   s   n  buffer1 buffer2      return 0      Ref  http   www cplusplus com reference cstring memcmp

User · Answer

if  iar1    iar2    Here iar1 and iar2 are decaying to pointers to the first elements of the respective arrays  Since they are two distinct arrays  the pointer values are  of course  different and your comparison tests not equal   To do an element-wise comparison  you must either write a loop  or use std  array instead   std  array lt int  5 gt  iar1  1 2 3 4 5   std  array lt int  5 gt  iar2  1 2 3 4 5    if  iar1    iar2          arrays contents are the same    else        not the same

User · Answer

If you are reluctant to change your existing code to std  array  then use a couple of methods instead which takes non-type template arguments      Passed arrays store different data types template  lt typename T  typename U  int size1  int size2 gt  bool equal T   amp arr1  size1   U   amp arr2  size2         return false       Passed arrays store SAME data types template  lt typename T  int size1  int size2 gt  bool equal T   amp arr1  size1   T   amp arr2  size2         if size1    size2            for int i   0   i  lt  size1    i               if arr1 i     arr2 i   return false                    return true            return false      Here is the demo  Note that  while calling  we just need to pass the array variables e g  equal iar1  iar2  in your case  no need to pass the size of arrays

User · Answer

You are comparing the addresses instead of the values

User · Answer

If you are willing to use std  array instead of built-in arrays  you may use  std  array lt int  5 gt  iar1    1 2 3 4 5   std  array lt int  5 gt  iar2    1 2 3 4 5    if  iar1    iar2

[c++] Comparing arrays for equality in C++

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