How to set array length in c dynamically

Question

I am still new to C  and I ve been struggling with various issues on arrays  I ve got an array of metadata objects  name value pairs  and I would like to know how to create only the number of  InputProperty  objects that I truly need  In this loop I ve arbitrarily set the number of elements to 20 and I try to bail out when the entry becomes null but the web service on the receiving end of this does not like any null elements passed to it   private Update BuildMetaData MetaData   nvPairs        Update update   new Update        InputProperty   ip   new InputProperty 20       how to make this  dynamic      int i      for  i   0  i  lt  nvPairs Length  i                  if  nvPairs i     null  break          ip i    new InputProperty            ip i  Name    udf     nvPairs i  Name          ip i  Val   nvPairs i  Value            update Items   ip      return update      In summary  say I only have 3 namevalue pairs in the above input array  Rather than allocate 20 elements for the array called ip  how can code this so ip is only as big as it needs to be  The update object is passed across another webservice so serialization is important  i e  I can t use namevaluecollection  etc      p s  Is the only way to followup on a posted question through the  add comments  facility

User · Answer

You could use List inside the method and transform it to an array at the end  But i think if we talk about an max-value of 20  your code is faster       private Update BuildMetaData MetaData   nvPairs                Update update   new Update            List lt InputProperty gt  ip   new List lt InputProperty gt             for  int i   0  i  lt  nvPairs Length  i                          if  nvPairs i     null  break              ip i    new InputProperty                ip i  Name    udf     nvPairs i  Name              ip i  Val   nvPairs i  Value                    update Items   ip ToArray            return update

User · Answer

Does is need to be an array   If you use an ArrayList or one of the other objects available in C   you won t  have this limitation to content with   Hashtable  IDictionnary  IList  etc   all allow a dynamic number of elements

User · Answer

If you don t want to use a List  ArrayList  or other dynamically-sized collection and then convert to an array  that s the method I d recommend  by the way   then you ll have to allocate the array to its maximum possible size  keep track of how many items you put in it  and then create a new array with just those items in it   private Update BuildMetaData MetaData   nvPairs        Update update   new Update        InputProperty   ip   new InputProperty 20       how to make this  dynamic      int i      for  i   0  i  lt  nvPairs Length  i                  if  nvPairs i     null  break          ip i    new InputProperty             ip i  Name    udf     nvPairs i  Name          ip i  Val   nvPairs i  Value            if  i  lt  nvPairs Length                   Create new  smaller  array to hold the items we processed          update Items   new InputProperty i           Array Copy ip  update Items  i             else               update Items   ip            return update      An alternate method would be to always assign update Items   ip  and then resize if necessary   update Items   ip  if  i  lt  nvPairs Length        Array Resize update Items  i       It s less code  but will likely end up doing the same amount of work  i e  creating a new array and copying the old items

User · Answer

Use Array CreateInstance to create an array dynamically       private Update BuildMetaData MetaData   nvPairs                Update update   new Update            InputProperty   ip   Array CreateInstance typeof InputProperty   nvPairs Count    as InputProperty            int i          for  i   0  i  lt  nvPairs Length  i                          if  nvPairs i     null  break              ip i    new InputProperty                ip i  Name    udf     nvPairs i  Name              ip i  Val   nvPairs i  Value                    update Items   ip          return update

User · Answer

Use this    Array Resize ref myArr  myArr Length   5

User · Answer

Or in C  3 0 using System Linq you can skip the intermediate list   private Update BuildMetaData MetaData   nvPairs            Update update   new Update            var ip   from nv in nvPairs                  select new InputProperty                                           Name    udf     nv Name                       Val   nv Value                             update Items   ip ToArray            return update

User · Answer

You can create an array dynamically in this way    static void Main                    Create a string array 2 elements in length          int arrayLength   2          Array dynamicArray   Array CreateInstance typeof int   arrayLength           dynamicArray SetValue 234  0                                      a 0    234          dynamicArray SetValue 444  1                                      a 1    444          int number    int dynamicArray GetValue 0                              number   a 0             int   cSharpArray    int   dynamicArray          int s2   cSharpArray 0

User · Answer

Typically  arrays require constants to initialize their size   You could sweep over nvPairs once to get the length  then  dynamically  create an array using a variable for length like this   InputProperty   ip    InputProperty   Array CreateInstance typeof InputProperty   length     I wouldn t recommend it  though   Just stick with the  List lt InputProperty gt  ip           update Items   ip ToArray      solution   It s not that much less performant  and way better looking

User · Answer

InputProperty   ip   new InputProperty nvPairs Length      Or  you can use a list like so   List lt InputProperty gt  list   new List lt InputProperty gt     InputProperty ip   new       list Add ip   update items   list ToArray      Another thing I d like to point out  in C  you can delcare your int variable use in a for loop right inside the loop   for int i   0  i lt nvPairs Length i             And just because I m in the mood  here s a cleaner way to do this method IMO   private Update BuildMetaData MetaData   nvPairs            Update update   new Update            var ip   new List lt InputProperty gt              foreach var nvPair in nvPairs                        if  nvPair    null  break              var inputProp   new InputProperty                              Name    udf     nvPair Name                 Val   nvPair Value                            ip Add inputProp                     update Items   ip ToArray            return update

[c#] How to set array length in c# dynamically

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