Trying to pass 1 struct values from 1 contract to other struct in 2nd contract

Question

contract old{
    struct Student{
        bytes32 name;
        uint age;
    }
    uint public sno = 0;
    mapping (uint => Student) pupil;
    function input(bytes32 n, uint a){
        <Student updated>
    }
    function output() constant returns(bytes32[], uint[], uint){
        bytes32[] memory n = new bytes32[](sno);
        uint[] memory a = new uint[](sno);
        for(uint i=0; i<sno; i++){
            Student s = pupil[i+1];
            n[i] = s.name;
            a[i] = s.age;
        }
        return(n,a,sno);
    }
}


contract receiver{
    old o;
    struct Student1{
        bytes32 name1;
        uint age1;
    }
    uint public sno1 = 0;
    mapping (uint => Student) pupil;
    function set(){
      ........
    }
}

Want to copy struct in contract old to struct in contract receiver. I know struct can not be acceseed directly in another contract but want to do it through array.

Answer 1

There's way too much going on here. As general guidance, I'd avoid for loops as much as possible in Solidity. It's often a red flag.

Here's some code that compiles. Have a look at the the way receiver refers to old with reference to its known address on the blockchain. You can solve it a different way but it's important to solve it.

pragma solidity ^0.4.6;

contract Old {

  struct Thing {
    uint x;
    uint y;
  }

  Receiver r;

  function Old() {
    // When you deploy Old, you also deploy Receiver. See comment near line 25.
    r = new Receiver();
  }

  // 10 items per list is arbitrary size. It makes the interface static in size.
  // You can only pass dynamic sized elements between functions in the same contract.
  function output() returns(bytes32[10] n, uint[10] a, uint sno, uint x, uint y) {
    // do stuff

    Thing memory thing;
    thing.x = 1;
    thing.y = 2;
    return(n,a,sno,thing.x, thing.y); 
  }

  function getReceiver() returns(address receiver) {
    return r;
  }
}

contract Receiver {

  struct Thing {
    uint x;
    uint y;
  }

  address old;

  function Receiver() {
    old = msg.sender;
  }

  function pull() returns(bytes32[10] en, uint[10] ay, uint snow, uint ex, uint why) {
    Old o = Old(old); // needs to the address of "Old" somehow.
    Thing memory thing;
    bytes32[10] memory n;
    uint[10] memory a;
    uint sno;
    (n, a, sno, thing.x, thing.y) = o.output();
    return (n,a,sno,thing.x, thing.y);
    }
  }