Data Location Assignment

santiago · March 3, 2021, 9:49pm

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         users[id].balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

Omas · March 5, 2021, 8:23am

pragma solidity 0.7.5;

contract MemoryandStorage {

mapping(uint => User) users;

struct User {
    uint id;
    uint balance;
}

function addUser(uint id, uint balance) public {
    //User memory newUser = User(_id, _balance);
    users[id] = User(id, balance);
}

function updateBalance(uint id, uint balance) public {
    User storage user = users[id];
    user.balance = balance;
}

function getBalance(uint id) public view returns(uint) {
    return users[id].balance;
}

}

marsrvr · March 5, 2021, 5:11pm

Local “user” buffer of the User struct instance is wasteful and dropped upon function exiting.

    function updateBalance(uint id, uint balance) public {
         User memory user = users[id];
         user.balance = balance;
    }

Replace it with a direct assignment to the state variable mapping:

    function updateBalance(uint id, uint balance) public {
         users[id].balance = balance;
    }

leemac · March 6, 2021, 12:18am

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         User storage user = users[id];
         user.balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

Baidis · March 6, 2021, 12:55pm

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         User storage user = users[id];
         user.balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

Baidis · March 6, 2021, 12:59pm

Thanks I assumed there was a way to do this but everything I tried was wrong and would not compile. Always something new to learn.

Mehdi369 · March 6, 2021, 2:25pm

users[id].balance = balance;

Leenez · March 7, 2021, 6:40pm

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         users[id].balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

blabtonic · March 7, 2021, 11:39pm

Hello
Here is the answer for the code.

the change was changing User memory user to User storage user. We need this as a storage to save the user data in-between function calls. The storage data location can help with that.

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         User storage user = users[id];
         user.balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }
}

Hector_Martinez · March 8, 2021, 2:54am

In the updateBalance function, I replaced the keyword Memory with Storage. This is done to declare a struct member using the Storage keyword.

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         User storage user = users[id];
         user.balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

n1g3 · March 8, 2021, 3:57pm

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         User storage user = users[id];
         user.balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

kdivus · March 9, 2021, 10:56am

pragma solidity 0.7.5;


contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    // added storage keyword instead of memory
    function updateBalance(uint id, uint balance) public {
         User storage user = users[id];
         user.balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

CryptoPhoenix · March 9, 2021, 4:40pm

Under the updateBalance function, replace memory with storage. Memory is only stored inside the function, but storage is stored for the whole contract, so the contract was “forgetting” the change made to the user’s balance once the updateBalance function was done running.

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         User storage user = users[id];
         user.balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

mikeB · March 10, 2021, 3:57pm

My solution correct users mapping in updateBalance and add option to add to current balance.

pragma solidity 0.7.5;
contract MemoryAndStorage {

mapping(uint => User) users;

struct User{
    uint id;
    uint balance;
}

function addUser(uint id, uint balance) public {
    users[id] = User(id, balance);
}

function updateBalance(uint id, uint balance) public {
    
    // incorrect memory use!!!!!
    // User memory user = users[id];
    // user.balance = balance;

    users[id].balance= balance;   // replace balance.
    
   //users[id].balance += balance;// add to existing balance total.
    
    
}

function getBalance(uint id) view public returns (uint) {
    return users[id].balance;
}

}

Melshman · March 11, 2021, 3:19am

function updateBalance(uint id, uint balance) public {
     //User memory user = users[id];
    // user.balance = balance;
    users[id].balance = balance;
}

Michal_Kosior · March 11, 2021, 7:50am

pragma solidity 0.7.5;

contract MemoryAndStorage {

mapping(uint => User) users;

struct User{
    uint id;
    uint balance;
}

function addUser(uint id, uint balance) public {
    users[id] = User(id, balance);
}

function updateBalance(uint id, uint balance) public {
     users[id].balance = balance;
}

function getBalance(uint id) view public returns (uint) {
    return users[id].balance;
}

}

LukeS · March 12, 2021, 4:19am

pragma solidity 0.7.5;
contract MemoryAndStorage {

mapping(uint => User) users;

struct User{
    uint id;
    uint balance;
}

function addUser(uint id, uint balance) public {
    users[id] = User(id, balance);
}

function updateBalance(uint id, uint balance) public  {
     User storage user = users[id]; //changed memory to storage
     user.balance = balance;
}

function getBalance(uint id) view public returns (uint) {
    return users[id].balance;
}

}

zero0_cero · March 12, 2021, 11:21am

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalanceMine(uint _id, uint _balance) public {
        
        User memory userMod =  User(_id, _balance);
        users[_id] = userMod;
    }
    
    /*function updateBalance(uint id, uint balance) public {
         User memory user = users[id];
         user.balance = balance;
    }*/

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }
}

Thats my solution

Bozidar · March 13, 2021, 10:02pm

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         User storage user = users[id];
         user.balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}

Astro · March 14, 2021, 3:04pm

pragma solidity 0.7.5;
contract MemoryAndStorage {

    mapping(uint => User) users;

    struct User{
        uint id;
        uint balance;
    }

    function addUser(uint id, uint balance) public {
        users[id] = User(id, balance);
    }

    function updateBalance(uint id, uint balance) public {
         users[id].balance = balance;
    }

    function getBalance(uint id) view public returns (uint) {
        return users[id].balance;
    }

}