Solidity – Can Arrays in Mappings Be Modified?

arraysmappingsolidity

I have created a mapping which gives an array of structs.

mapping(address => BetByUser[]) betsByAddress;

I have tried changing this array, but with no success. Are these arrays in memory or storage? Can I change them, if yes, how?

Best Answer

Yes I coded up something, take a look, uncomment the part and change the parameter types for the respective part. Try to understand the following code, I have added some comments for better understanding.

pragma solidity ^0.4.0;

contract myContract
{

// a structure that stores bets

struct Bets{
    uint betNum; // some int number
}

mapping(address => Bets[]) myBetMapping;

function addBet(uint n) returns(uint)
{
    Bets memory l;
    l.betNum = n;
    myBetMapping[msg.sender].push(l);

   //check the last bet is added or not

   return myBetMapping[msg.sender][myBetMapping[msg.sender].length -1].betNum;

}

// lets modify the mapping and the array

function modifyBet(uint n, uint index) returns(uint,uint,uint)
{
    /*
    Bets memory l;
    l.betNum = n;

    add new bet

    myBetMapping[msg.sender].push(l);
    return myBetMapping[msg.sender][myBetMapping[msg.sender].length -1].betNum;
    */
    /*
    add new bet at index

     delete myBetMapping[msg.sender][index];
     myBetMapping[msg.sender][index] = l;

     // return the added value

     return myBetMapping[msg.sender][index].betNum;
    */
    /*
    deleting a bet and reducing the length , (index starts from 0)

    //delete the struct 

    delete myBetMapping[msg.sender][index];

    for(uint i = index ;i<myBetMapping[msg.sender].length-1; i++)
    {
        // shifts value to left
        myBetMapping[msg.sender][i] =  myBetMapping[msg.sender][i+1];

    }

     //deleting the last value
     delete myBetMapping[msg.sender][myBetMapping[msg.sender].length-1];

     //reducing the length
     myBetMapping[msg.sender].length--;

     //checking evrything works fine or not by returning the last value, the second last and the length
     return (myBetMapping[msg.sender][index].betNum,myBetMapping[msg.sender][myBetMapping[msg.sender].length-1].betNum,myBetMapping[msg.sender].length);
    */
}
}

//This should solve your problem :) enjoy!

Related Solutions

Solidity Arrays – Help Using and Reading Arrays and Mappings in Solidity

Here are some patterns that might help you out.

pragma solidity ^0.4.15;

contract Storage {

    struct PlayerStruct {
        uint meaningless;
        uint[] dynamicList;
        uint[10] fixedList;
        mapping(bytes32 => uint) keyToUintMap;
    }

    mapping(address => PlayerStruct) public playerStructs;

    function getPlayerDynListLength(address player) public constant returns(uint count) {
        return playerStructs[player].dynamicList.length;
    }

    function appendPlayerDynList(address player, uint value) public returns(uint length) {
        return playerStructs[player].dynamicList.push(value);
    }

    function setPlayerDynFixedList(address player, uint index, uint value) public returns(bool success) {
        require(index <= 9);
        playerStructs[player].fixedList[index] = value;
        return true;
    }

    function getPlayerDynamicListElement(address player, uint index) public constant returns(uint value) {
        return playerStructs[player].dynamicList[index];
    }

    function setPlayerMappedElement(address player, bytes32 key, uint value) public returns(bool success) {
        playerStructs[player].keyToUintMap[key] = value;
        return true;
    }

    function getPlayerMappedElement(address player, bytes32 key) public constant returns(uint value) {
        return playerStructs[player].keyToUintMap[key];
    }

}

Update:

Here it is in Remix to show it working:

Hope it helps.

Solidity – How are Mappings Found in Storage in Geth?

I finally solved it.

The key is the actual key in the array.
The pos is the displacement of that data definition from the start of the contract storage.

Then to solve this you just put the key (ie the address) into the a key+pos sha3 and convert to a bigNumber. The vital part also is to remove 0x and to format as 64 chars.

Here is the final output -

> key
"00000000000000000000000046fb9a22689c4a4bfb494baeafbb8b2993725305"
> key1
"000000000000000000000000f07044ba718e8eb25850be0e534f9522018784be"
> pos
"0000000000000000000000000000000000000000000000000000000000000001"
>

Pos is 1 because I added a uint to the contract before the mapping to test this. The two keys are then the accounts with 0x removed and reformatted to 64 chars. ie.

> eth.coinbase
"0x46fb9a22689c4a4bfb494baeafbb8b2993725305"
> eth.accounts[1]
"0xf07044ba718e8eb25850be0e534f9522018784be"

> bn=web3.sha3(key + pos, {"encoding":"hex"})
"0x4a6915a70ddb253ab9075c26d94720491095a5a0a6d31c6720a4db10b12f661e"

> bn1=web3.sha3(key1 + pos, {"encoding":"hex"})
"0x4ecac4dae9466f9f535b4d7b3d80aedd57bdd0e6e6e74425ed865c2fa5e20707"

> sn1=web3.toBigNumber(bn1)
3.5638663940699095975789856456193070520684880277631386156092330925546436429575e+76

> sn=web3.toBigNumber(bn)
3.3656819177407030101749625369691302081266253965792325840314023187955028289054e+76

> eth.getStorageAt(con.address,sn1)
"0x0000000000000000000000000000000000000000000000000000000000001770"

> eth.getStorageAt(con.address,sn)
"0x0000000000000000000000000000000000000000000000000000000000001edc"

> con.getAddressBalance(eth.coinbase)
7900
> con.getAddressBalance(eth.accounts[1])
6000

Here is the amended contract -

pragma solidity ^0.4.18;

contract CA4 {

uint public pos;
mapping(address=>uint16) public balances;

function getBalance() view returns (uint16) {
uint16 mybalance = balances[msg.sender];
return mybalance;
}

function getAddressBalance (address myaddress) view returns (uint16) {
return balances[myaddress];
}

function setAddressBalance(address myaddress, uint16 newbalance) public {
pos=9;
balances[myaddress]=newbalance;
}

function setBalance(uint16 newbalance) public {
pos=9;
balances[msg.sender]=newbalance;
}


}

Best Answer

Related Solutions

Solidity Arrays – Help Using and Reading Arrays and Mappings in Solidity

Solidity – How are Mappings Found in Storage in Geth?

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