Comparing values of fetched data with input data of different contracts

Question

Given two contracts as follows, contract TestData calls contract Reg to fetch data that had already been stored in its map using get_attributes function.

pragma solidity ^0.4.21;
contract Reg {
    mapping (address=>bytes32[5]) Map;

    //Filling the map
    function fill_map(bytes32[5] _attributes) public  {
            Map[msg.sender] = _attributes;
    }

    //Returns data in the map corresponding to an address
    function get_attributes(address _id) view public returns (bytes32[5]){
        return Map[_id];
    }
}


contract TestData {

    address Address;
    function get_address (address _Address) public{   
        Address = _Address;
    } 

    //Retreive data from Reg contract
    bytes32[5] fetched;
    function fetch(address _reg_Adress) public view returns (bytes32[5]) {
        Reg r = Reg(_reg_Adress);
        fetched = r.get_attributes(Address);
        return (fetched);
    }

    //Retreive input data from user
    bytes32[5] inputs;
    function getInputs(bytes32[5] _inputs) public view returns (bytes32[5]){
            inputs = _inputs;
            return (inputs);
    }    

    //Compare input data with fetched data
    bool[5] a = [false,false,false,false,false];
    function compare() public view returns(bool[5]){
        for(uint i=0;i<5;i++){
            for(uint j=0;j<5;j++){
                if(inputs[i] == fetched[j]){
                    a[i] = true;                 
                }
            }
        }

        return (a);
    }  

}

This is how I test it:

1. Fill the map with ["0x0","0x1","0x2","0x3","0x4"]

2. For user input I also input ["0x0","0x1","0x2","0x3","0x4"]

The output is correct returning [true,true,true,true,true].

However, if I change the input say, ["0xA","0x1","0x2","0x3","0x4"], the output remains [true,true,true,true,true] although it should be [false,true,true,true,true].

Does something happen to the data as it is being fetched from the Reg contract? When I try testing the same code but with two input arrays rather than fetching the data, it works fine.

Also, I have been looking for other ways to do the comparisons. Is there any other efficient way other than looping?

Answer 1

The function compare is almost right, the errors are elsewhere

function fetch(address _reg_Adress) public view returns (bytes32[5])

you have to remove view from here

function getInputs(bytes32[5] _inputs) public view returns (bytes32[5])

also from here.

Then move your array into the function and define it as memory.

//Compare input data with fetched data
function compare() public view returns(bool[5]){
    bool[5] memory a = [false,false,false,false,false];

    for(uint i=0;i<5;i++){
        for(uint j=0;j<5;j++){
            if(inputs[i] == fetched[j]){
                a[i] = true;                 
            }
        }
    }

    return (a);
}

if not, you should remove view also from the method compare to make it work

after this changes the result would be false,true,true,true,true as expected.

Answer 2

There are several issues:

First your for loop is stopping early, at 3 when the limit should be i<5.

Also your second for is not necessary. Your function can be:

function compare() public view returns(bool[5]){
    bool[5] memory a;
    for(uint i=0;i<5;i++){
        for(uint j=0;j<5;j++){
            if(inputs[i] == fetched[j]){
                a[i] = true;                 
            }
        }
    }

    return (a);
}  

You could also do the follwoing to ensure a is updated etither when the values is true or false:

function compare() public view returns(bool[5]){
    bool[5] memory a;
    for(uint i=0;i<5;i++){
        for(uint j=0;j<5;j++){
            a[i] = (inputs[i] == fetched[j]);                 
        }
    }

    return (a);
}  

finally, your functions modify state variables so these cannot be view.

Hope this helps

UPDATE: Full code.

pragma solidity ^0.4.21;
contract Reg {
    mapping (address=>bytes32[5]) public Map;

    //Filling the map
    function fill_map(bytes32[5] _attributes) public  {
            Map[msg.sender] = _attributes;
    }

    //Returns data in the map corresponding to an address
    function get_attributes(address _id) view public returns (bytes32[5]){
        return Map[_id];
    }
}


contract TestData {

    address Address;
    function get_address (address _Address) public{   
        Address = _Address;
    } 

    //Retreive data from Reg contract
    bytes32[5] public fetched;
    function fetch(address _reg_Adress) public returns (bytes32[5]) {
        Reg r = Reg(_reg_Adress);
        fetched = r.get_attributes(Address);
        return (fetched);
    }

    //Retreive input data from user
    bytes32[5] public inputs;
    function getInputs(bytes32[5] _inputs) public returns (bytes32[5]){
            inputs = _inputs;
            return (inputs);
    }    

    //Compare input data with fetched data

    function compare() public view returns(bool[5]){
        bool[5] memory a;
        for(uint i=0;i<5;i++){
            for(uint j=0;j<5;j++){
                if(inputs[i] == fetched[j]){
                    a[i] = true;                 
                }
            }
        }

        return (a);
    }  

}