Returning an array inside a structure that was allocated in afunction

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  • ctj951
    #1

    Returning an array inside a structure that was allocated in afunction

    I have a very specific question about a language issue that I was
    hoping to get an answer to. If you allocate a structure that contains
    an array as a local variable inside a function and return that
    structure, is this valid?

    As shown in the code below I am allocating the structure in the
    function and then returning the structure. I know if the structure
    contained only simple types (int, float) this will work without
    problems as you are getting a copy of those items returned from the
    function. But I'm wondering with an array which is being returned
    from the function as part of the structure is a pointer to the local
    variable or perhaps a copy of that array (as it would be for simple
    types). I think we might be getting a pointer returned but I'm not
    sure.

    #include <iostream>
    using namespace std;

    struct Item
    {
    int itemNumber;
    int internalItems[5];
    };


    Item CreateItem()
    {
    Item newItem;

    newItem.itemNum ber = 10;

    newItem.interna lItems[ 0 ] = 1;
    newItem.interna lItems[ 1 ] = 2;
    newItem.interna lItems[ 2 ] = 3;
    newItem.interna lItems[ 3 ] = 7;
    newItem.interna lItems[ 4 ] = 9;

    return( newItem );
    }


    void PrintItem( Item iItemToPrint )
    {
    cout << iItemToPrint.in ternalItems[0];
    }


    int main ()
    {
    Item testItem = CreateItem();

    PrintItem( testItem );

    return 0;
    }

    This is a specific question about a specific language issue. Thank
    You.
    Tags: None
    • Leandro Melo
      #2
      Re: Returning an array inside a structure that was allocated in afunction

      On 13 nov, 14:46, ctj951 <chadsspameater em...@yahoo.com wrote:
      I have a very specific question about a language issue that I was
      hoping to get an answer to.  If you allocate a structure that contains
      an array as a local variable inside a function and return that
      structure, is this valid?
      >
      As shown in the code below I am allocating the structure in the
      function and then returning the structure.  I know if the structure
      contained only simple types (int, float) this will work without
      problems as you are getting a copy of those items returned from the
      function.  But I'm wondering with an array which is being returned
      from the function as part of the structure is a pointer to the local
      variable or perhaps a copy of that array (as it would be for simple
      types).  I think we might be getting a pointer returned but I'm not
      sure.
      >
      #include <iostream>
      using namespace std;
      >
      struct Item
         {
         int itemNumber;
         int internalItems[5];
         };
      >
      Item CreateItem()
         {
         Item newItem;
      >
         newItem.itemNum ber = 10;
      >
         newItem.interna lItems[ 0 ] = 1;
         newItem.interna lItems[ 1 ] = 2;
         newItem.interna lItems[ 2 ] = 3;
         newItem.interna lItems[ 3 ] = 7;
         newItem.interna lItems[ 4 ] = 9;
      >
         return( newItem );
         }
      >
      void PrintItem( Item iItemToPrint )
         {
         cout << iItemToPrint.in ternalItems[0];
         }
      >
      int main ()
         {
         Item testItem = CreateItem();
      >
         PrintItem( testItem );
      >
         return 0;
         }
      >
      This is a specific question about a specific language issue.  Thank
      You.


      This is one of the reasons copy constructors exist. ;) Think about
      which semantics you would like for a particular class (deep copy,
      shallow copy) and write a copy constructor accordingly.

      --
      Leandro T. C. Melo

        Comment

        • Bo Persson
          #3
          Re: Returning an array inside a structure that was allocated in a function

          ctj951 wrote:
          I have a very specific question about a language issue that I was
          hoping to get an answer to. If you allocate a structure that
          contains an array as a local variable inside a function and return
          that structure, is this valid?
          >
          As shown in the code below I am allocating the structure in the
          function and then returning the structure. I know if the structure
          contained only simple types (int, float) this will work without
          problems as you are getting a copy of those items returned from the
          function. But I'm wondering with an array which is being returned
          from the function as part of the structure is a pointer to the local
          variable or perhaps a copy of that array (as it would be for simple
          types). I think we might be getting a pointer returned but I'm not
          sure.
          >
          #include <iostream>
          using namespace std;
          >
          struct Item
          {
          int itemNumber;
          int internalItems[5];
          };
          >
          >
          Item CreateItem()
          {
          Item newItem;
          >
          newItem.itemNum ber = 10;
          >
          newItem.interna lItems[ 0 ] = 1;
          newItem.interna lItems[ 1 ] = 2;
          newItem.interna lItems[ 2 ] = 3;
          newItem.interna lItems[ 3 ] = 7;
          newItem.interna lItems[ 4 ] = 9;
          >
          return( newItem );
          }
          >
          >
          void PrintItem( Item iItemToPrint )
          {
          cout << iItemToPrint.in ternalItems[0];
          }
          >
          >
          int main ()
          {
          Item testItem = CreateItem();
          >
          PrintItem( testItem );
          >
          return 0;
          }
          >
          This is a specific question about a specific language issue. Thank
          You.
          This is quite ok. You are returning a struct, and all its members will
          be copied. There are no pointers involved.


          Bo Persson


            Comment

            • mail.dsp@gmail.com
              #4
              Re: Returning an array inside a structure that was allocated in afunction

              No need to think about it. Since in structure you've allocated memory
              at compile time therefore default copy constructor will be invoked and
              it will copy all the member of structure properly. Even it will work
              in case of assignment too. But in case of run time allocation you'll
              have to define your copy constructor(dee p copy) and overload
              assignment operator for proper functionality.

              --
              Daya S. Prasad

                Comment

                • Leandro Melo
                  #5
                  Re: Returning an array inside a structure that was allocated in afunction

                  On 13 nov, 15:02, Leandro Melo <ltcm...@gmail. comwrote:
                  On 13 nov, 14:46, ctj951 <chadsspameater em...@yahoo.com wrote:
                  >
                  >
                  >
                  I have a very specific question about a language issue that I was
                  hoping to get an answer to.  If you allocate a structure that contains
                  an array as a local variable inside a function and return that
                  structure, is this valid?
                  >
                  As shown in the code below I am allocating the structure in the
                  function and then returning the structure.  I know if the structure
                  contained only simple types (int, float) this will work without
                  problems as you are getting a copy of those items returned from the
                  function.  But I'm wondering with an array which is being returned
                  from the function as part of the structure is a pointer to the local
                  variable or perhaps a copy of that array (as it would be for simple
                  types).  I think we might be getting a pointer returned but I'm not
                  sure.
                  >
                  #include <iostream>
                  using namespace std;
                  >
                  struct Item
                     {
                     int itemNumber;
                     int internalItems[5];
                     };
                  >
                  Item CreateItem()
                     {
                     Item newItem;
                  >
                     newItem.itemNum ber = 10;
                  >
                     newItem.interna lItems[ 0 ] = 1;
                     newItem.interna lItems[ 1 ] = 2;
                     newItem.interna lItems[ 2 ] = 3;
                     newItem.interna lItems[ 3 ] = 7;
                     newItem.interna lItems[ 4 ] = 9;
                  >
                     return( newItem );
                     }
                  >
                  void PrintItem( Item iItemToPrint )
                     {
                     cout << iItemToPrint.in ternalItems[0];
                     }
                  >
                  int main ()
                     {
                     Item testItem = CreateItem();
                  >
                     PrintItem( testItem );
                  >
                     return 0;
                     }
                  >
                  This is a specific question about a specific language issue.  Thank
                  You.
                  >
                  This is one of the reasons copy constructors exist. ;) Think about
                  which semantics you would like for a particular class (deep copy,
                  shallow copy) and write a copy constructor accordingly.
                  Hmm... your array is statically allocated. No worry then.

                  --
                  Leandro T. C. Melo

                    Comment

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