How do I find the length of an array

Question

Is there a way to find how many values an array has   Detecting whether or not I ve reached the end of an array would also work

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Simply you can use this snippet    include  lt iostream gt   include  lt string gt   include  lt array gt   using namespace std   int main        array lt int 3 gt  values    cout  lt  lt   No  elements in valuea array     lt  lt  values size    lt  lt    elements    lt  lt  endl    cout  lt  lt   sizeof myints      lt  lt  sizeof values   lt  lt  endl       and here is the reference   http   www cplusplus com reference array array size

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For old g   compiler  you can do this  template  lt class T  size t N gt  char   amp helper T   amp   N    N     define arraysize array   sizeof helper array     int main         int a 10       std  cout  lt  lt  arraysize a   lt  lt  std  endl      return 0

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While this is an old question  it s worth updating the answer to C  17   In the standard library there is now the templated function std  size    which returns the number of elements in both a std container or a C-style array   For example    include  lt iterator gt   uint32 t data      10  20  30  40   auto dataSize   std  size data      dataSize    4

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As others have said  you can use the sizeof arr  sizeof  arr   but this will give you the wrong answer for pointer types that aren t arrays  template lt class T  size t N gt  constexpr size t size T   amp   N     return N     This has the nice property of failing to compile for non-array types  Visual Studio has  countof which does this   The constexpr makes this a compile time expression so it doesn t have any drawbacks over the macro  at least none I know of   You can also consider using std  array from C  11  which exposes its length with no overhead over a native C array  C  17 has std  size   in the  lt iterator gt  header which does the same and works for STL containers too  thanks to  Jon C

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Lets say you have an global array declared at the top of the page  int global       1  2  3  4      To find out how many elements are there  in c    in the array type the following code   sizeof global    4    The sizeof NAME OF ARRAY    4 will give you back the number of elements for the given array name

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Avoid using the type together with sizeof  as sizeof array  sizeof char   suddenly gets corrupt if you change the type of the array   In visual studio  you have the equivivalent if sizeof array  sizeof  array   You can simply type  countof array

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Doing sizeof  myArray   will get you the total number of bytes allocated for that array  You can then find out the number of elements in the array by dividing by the size of one element in the array  sizeof  myArray 0

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Just a thought  but just decided to create a counter variable and store the array size in position  0    I deleted most of the code I had in the function but you ll see after exiting the loop  prime 0  is assigned the final value of  a   I tried using vectors but VS Express 2013 didn t like that very much   Also make note that  a  starts at one to avoid overwriting  0  and it s initialized in the beginning to avoid errors   I m no expert  just thought I d share    int prime      0   int primes int x  int y       using namespace std  int a   1      for  int i   x  i  lt   y  i    prime a    i  a          prime 0    a  return 0

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If you mean a C-style array  then you can do something like   int a 7   std  cout  lt  lt   Length of array      lt  lt   sizeof a  sizeof  a    lt  lt  std  endl    This doesn t work on pointers  i e  it won t work for either of the following    int  p   new int 7   std  cout  lt  lt   Length of array      lt  lt   sizeof p  sizeof  p    lt  lt  std  endl    or   void func int  p        std  cout  lt  lt   Length of array      lt  lt   sizeof p  sizeof  p    lt  lt  std  endl     int a 7   func a     In C    if you want this kind of behavior  then you should be using a container class  probably std  vector

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sizeof array name  gives the size of whole array and sizeof int  gives the size of the data type of every array element   So dividing the size of the whole array by the size of a single element of the array gives the length of the array    int array name      1  2  3  4  5  6    int length   sizeof array name  sizeof int

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A good solution that uses generics   template  lt typename T unsigned S gt  inline unsigned arraysize const T   amp v  S     return S      Then simply call arraysize  Array   to get the length of the array   Source

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ANSWER  int number of elements   sizeof array  sizeof array 0    EXPLANATION  Since the compiler sets a specific size chunk of memory aside for each type of data  and an array is simply a group of those  you simply divide the size of the array by the size of the data type  If I have an array of 30 strings  my system sets aside 24 bytes for each element string  of the array  At 30 elements  that s a total of 720 bytes  720 24    30 elements  The small  tight algorithm for that is  int number of elements   sizeof array  sizeof array 0   which equates to number of elements   720 24 Note that you don t need to know what data type the array is  even if it s a custom data type

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This is pretty much old and legendary question and there are already many amazing answers out there  But with time there are new functionalities being added to the languages  so we need to keep on updating things as per new features available   I just noticed any one hasn t mentioned about C  20 yet  So thought to write answer   C  20  In C  20  there is a new better way added to the standard library for finding the length of array i e  std ssize    This function returns a signed value    include  lt iostream gt   int main         int arr      1  2  3       std  cout  lt  lt  std  ssize arr       return 0      C  17  In C  17 there was a better way  at that time  for the same which is std  size   defined in iterator    include  lt iostream gt   include  lt iterator gt     required for std  size  int main        int arr      1  2  3       std  cout  lt  lt   Size is    lt  lt  std  size arr       return 0      P S  This method works for vector as well   Old  This traditional approach is already mentioned in many other answers    include  lt iostream gt   int main         int array       1  2  3        std  cout  lt  lt  sizeof array    sizeof array 0        return 0      Just FYI  if you wonder why this approach doesn t work when array is passed to another function  The reason is   An array is not passed by value in C    instead the pointer to array is passed  As in some cases passing the whole arrays can be expensive operation  You can test this by passing the array to some function and make some changes to array there and then print the array in main again  You ll get updated results   And as you would already know  the sizeof   function gives the number of bytes  so in other function it ll return the number of bytes allocated for the pointer rather than the whole array  So this approach doesn t work   But I m sure you can find a good way to do this  as per your requirement   Happy Coding

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I personally would suggest  if you are unable to work with specialized functions for whatever reason  to first expand the arrays type compatibility past what you would normally use it as  if you were storing values   0   unsigned int x   - gt  int x     than you would make the array 1 element bigger than you need to make it  For the last element you would put some type that is included in the expanded type specifier but that you wouldn t normally use e g  using the previous example the last element would be -1  This enables you  by using a for loop  to find the last element of an array

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One of the most common reasons you would end up looking for this is because you want to pass an array to a function  and not have to pass another argument for its size   You would also generally like the array size to be dynamic   That array might contain objects  not primitives  and the objects maybe complex such that size of   is a not safe option for calculating the count     As others have suggested  consider using an std  vector or list  etc in instead of a primitive array   On old compilers  however  you still wouldn t have the final solution you probably want by doing simply that though  because populating the container requires a bunch of ugly push back   lines  If you re like me  want a single line solution with anonymous objects involved   If you go with STL container alternative to a primitive array  this SO post may be of use to you for ways to initialize it  What is the easiest way to initialize a std  vector with hardcoded elements   Here s a method that I m using for this which will work universally across compilers and platforms   Create a struct or class as container for your collection of objects   Define an operator overload function for  lt  lt    class MyObject   struct MyObjectList       std  list lt MyObject gt  objects      MyObjectList amp  operator lt  lt   const MyObject o                  objects push back  o            return  this              You can create functions which take your struct as a parameter  e g     someFunc  MyObjectList  amp objects      Then  you can call that function  like this   someFunc  MyObjectList    lt  lt  MyObject 1   lt  lt   MyObject 2   lt  lt   MyObject 3       That way  you can build and pass a dynamically sized collection of objects to a function in one single clean line

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std  vector has a method size   which returns the number of elements in the vector    Yes  this is tongue-in-cheek answer

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You have a bunch of options to be used to get a C array size   int myArray      0  1  2  3  4  5  7    1  sizeof  lt array gt     sizeof  lt type gt     std  cout  lt  lt   Size    lt  lt  sizeof myArray    sizeof int   lt  lt  std  endl    2  sizeof  lt array gt     sizeof   lt array gt     std  cout  lt  lt   Size    lt  lt  sizeof myArray    sizeof  myArray   lt  lt  std  endl    3  sizeof  lt array gt     sizeof  lt array gt   lt element gt      std  cout  lt  lt   Size    lt  lt  sizeof myArray    sizeof myArray 0    lt  lt  std  endl

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you can find the length of an Array by following   int  arr      1  2  3  4  5  6    int size      amp arr   1  - arr   cout  lt  lt   Number of elements in arr   is   lt  lt  size   return 0

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For C   CX  when writing e g  UWP apps using C   in Visual Studio  we can find the number  of values in an array by  simply using the size   function   Source Code   string myArray        Example1    Example2    Example3    Example4     int size of array size myArray     If you cout the size of array the output will be    gt  gt  gt  4

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In C    using the std  array class to declare an array  one can easily find the size of an array and also the last element    include lt iostream gt   include lt array gt  int main         std  array lt int 3 gt  arr         To find the size of the array     std  cout lt  lt arr size   lt  lt std  endl         Accessing the last element     auto it arr end        std  cout lt  lt arr back   lt  lt   t  lt  lt arr arr size  -1  lt  lt   t  lt  lt   --it        return 0        In fact  array class has a whole lot of other functions which let us use array a standard container  Reference 1 to C   std  array class Reference 2 to std  array class The examples in the references are helpful

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There s also the TR1 C  11 C  17 way  see it Live on Coliru    const std  string s 3       1 s   2 s   3 s    constexpr auto n         std  extent lt    decltype s   gt   value     From  lt type traits gt  constexpr auto n2        std  extent v lt  decltype s   gt             C  17 shorthand  const auto     a      std  array   1 s   2 s   3 s         C  17 class template arg deduction -- http   en cppreference com w cpp language class template argument deduction constexpr auto size   std  tuple size v lt  decltype a   gt    std  cout  lt  lt  n  lt  lt       lt  lt  n2  lt  lt       lt  lt  size  lt  lt    n      Prints 3 3 3

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Since C  11  some new templates are introduced to help reduce the pain when dealing with array length  All of them are defined in header  lt type traits gt    std  rank lt T gt   value If T is an array type  provides the member constant value equal to the number of dimensions of the array  For any other type  value is 0   std  extent lt T  N gt   value If T is an array type  provides the member constant value equal to the number of elements along the Nth dimension of the array  if N is in  0  std  rank lt T gt   value   For any other type  or if T is array of unknown bound along its first dimension and N is 0  value is 0   std  remove extent lt T gt   type If T is an array of some type X  provides the member typedef type equal to X  otherwise type is T  Note that if T is a multidimensional array  only the first dimension is removed   std  remove all extents lt T gt   type If T is a multidimensional array of some type X  provides the member typedef type equal to X  otherwise type is T    To get the length on any dimension of a multidimential array  decltype could be used to combine with std  extent  For example   include  lt iostream gt   include  lt type traits gt     std  remove extent std  remove all extents std  rank std  extent  template lt class T  size t N gt  constexpr size t length T  amp   N     return N     template lt class T  size t N gt  constexpr size t length2 T  amp arr  N     return sizeof arr    sizeof  arr      int main         int a 5  4  3    1 2 3    4 5 6           7 8 9             New way     constexpr auto l1   std  extent lt decltype a  gt   value         5     constexpr auto l2   std  extent lt decltype a   1 gt   value      4     constexpr auto l3   std  extent lt decltype a   2 gt   value      3     constexpr auto l4   std  extent lt decltype a   3 gt   value      0         Mixed way     constexpr auto la   length a         constexpr auto lpa   length  a       compile error       auto lpa   length  a       get at runtime     std  remove extent lt decltype a  gt   type pa      get at compile time       std  remove reference lt decltype  a  gt   type pa      same as above     constexpr auto lpa   length pa       std  cout  lt  lt  la  lt  lt       lt  lt  lpa  lt  lt    n           Old way     constexpr auto la2   sizeof a    sizeof  a       constexpr auto lpa2   sizeof  a    sizeof   a       std  cout  lt  lt  la2  lt  lt       lt  lt  lpa2  lt  lt    n        return 0     BTY  to get the total number of elements in a multidimentional array  constexpr auto l   sizeof a    sizeof std  remove all extents lt decltype a  gt   type    Or put it in a function template   include  lt iostream gt   include  lt type traits gt        template lt class T gt  constexpr size t len T  amp a        return sizeof a    sizeof typename std  remove all extents lt T gt   type      int main         int a 5  4  3    1 2 3    4 5 6           7 8 9         constexpr auto ttt   len a       int i      std  cout  lt  lt  ttt  lt  lt       lt  lt  len i   lt  lt    n            return 0     More examples of how to use them could be found by following the links

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Is there a way to find how many values an array has     Yes   Try sizeof array  sizeof array 0       Detecting whether or not I ve reached the end of an array would also work    I dont see any way for this unless your array is an array of characters  i e string    P S   In C   always use std  vector  There are several inbuilt functions and an extended functionality

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I provide a tricky solution here    You can always store length in the first element      malloc new  arr 0    length  arr        do anything   int len     arr-1    free --arr      The cost is you must --arr when invoke free

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Here is one implementation of ArraySize from Google Protobuf    define GOOGLE ARRAYSIZE a        sizeof a    sizeof   a      static cast lt size t gt    sizeof a    sizeof   a          test codes    char  ptr        you    are    here     int testarr      1  2  3  4   cout  lt  lt  GOOGLE ARRAYSIZE testarr   lt  lt  endl  cout  lt  lt  GOOGLE ARRAYSIZE ptr   lt  lt  endl       ARRAYSIZE arr  works by inspecting sizeof arr   the   of bytes in    the array  and sizeof   arr    the   of bytes in one array    element    If the former is divisible by the latter  perhaps arr is    indeed an array  in which case the division result is the   of    elements in the array   Otherwise  arr cannot possibly be an array     and we generate a compiler error to prevent the code from    compiling       Since the size of bool is implementation-defined  we need to cast      sizeof a   amp  sizeof   a    to size t in order to ensure the final    result has type size t       This macro is not perfect as it wrongfully accepts certain    pointers  namely where the pointer size is divisible by the pointee    size   Since all our code has to go through a 32-bit compiler     where a pointer is 4 bytes  this means all pointers to a type whose    size is 3 or greater than 4 will be  righteously  rejected

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include  lt iostream gt   int main          using namespace std      int arr      2  7  1  111       auto array length   end arr  - begin arr       cout  lt  lt   Length of array     lt  lt  array length  lt  lt  endl

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Instead of using the built in array function aka    int x 3     0  1  2     you should use the array class and the array template  Try    include  lt array gt  array lt type of the array  number of elements in the array gt  Name of Array         So now if you want to find the length of the array  all you have to do is using the size function in the array class   Name of Array size      and that should return the length of elements in the array

[c++] How do I find the length of an array?

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