Data Location Assignment [OLD]

camarosan · November 19, 2020, 11:38pm

this is my solution.
excuse me I changed a little the function addUser because you can change balance with this function when the id is already in use. I changed a little the code for this function to avoid update the balance for an id that already exist and an id = 0; Thanksss :)))

ironmaiden1541 · November 20, 2020, 9:45am

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

I believe the answer is to use the word storage because memory is only used with structs, string ,ect. not with uint types , since that is what we are using for our contract code.

ironmaiden1541 · November 20, 2020, 9:46am

nice…throwing an error message if the certain user id is in use. cool.

SimpleSimon · November 22, 2020, 3:04am

pragma solidity 0.5.1;
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 {
     // changed from memory to storage type
     User storage user = users[id];
     user.balance = balance;
}

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

}

Solution: changed from memory to storage type in updateBalance()

haianhnc · November 23, 2020, 7:35am

user on function updateBalance is save in memory so it lose after function executed. fix as
users[id] = user
or users[id].balance = balance

Crypto_Craven · November 23, 2020, 1:49pm

pragma solidity 0.5.1;
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;
}

}

Crypto_Craven · November 23, 2020, 2:10pm

Am I understanding correctly that the following are functionally the same?

users[id].balance = balance;

AND

User user storage = users[id];
user.balance = balance;

no need to update the object in the mapping as the storage keyword maintains the reference?

users[id] = user; <-- don’t need this?

HeigoH · November 23, 2020, 6:59pm

Also used storage instead

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

PapatoniC · November 24, 2020, 3:11pm

My solution is to save the balance into the users mapping before ending the updateBalance function. In the original code , is saved only in the user variable that stores only while the function runs , so it is lost when it finishes.

I just added in updateBalance function the following:
users[id].balance = user.balance;

// Full code:

pragma solidity 0.5.1;
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 memory user = users[id];
     user.balance = balance;
     users[id].balance = user.balance;
}

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

}

RikkeHrab · November 24, 2020, 3:35pm

pragma solidity 0.5.12;
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 memory user = users[id];
     users[id].balance = balance;
}

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

}

zanjakobjez · November 25, 2020, 5:27pm

pragma solidity 0.5.1;

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;
}

}

mariolux · November 26, 2020, 3:33pm

Well, I found 2 solutions, not sure if one is preferred over the other.

pragma solidity 0.5.12;
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 {
        
        // solution 1, store in storage instead of memory
        // User storage user = users[id];
        // user.balance = balance;
        
        // solution 2, store in users mapping since it is a state variable
         users[id].balance = balance; 
    }

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

}

barnabas · November 26, 2020, 10:03pm

Hi Guys

Solution 1: I changed memory to storage and then the update worked.

Solution 2: I copy pasted the body of the addUser function into the updateBalance function. It’s stupid but also worked…

Solution 3: in updateBalance I replace the body with users[id].balance = balance; Also stupid but worked.

The problem is that these “solutions” not only update the balance, but also add a user, if I add another number in the input field.

Cheers

waka · November 27, 2020, 6:25pm

pragma solidity 0.5.12;
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;
    }

}

TonyKutunio · November 27, 2020, 10:49pm

pragma solidity 0.5.1;
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;
}

}

bertrand282 · November 28, 2020, 5:25pm

pragma solidity 0.5.1;
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;
}

}

cawilson · November 28, 2020, 11:57pm

You need to change “memory” to “storage” on line 16 in the updateBalance function.
…
function updateBalance(uint id, uint balance) public {
User storage user = users[id];
user.balance = balance;
}
…

ChrisPap · November 29, 2020, 1:20pm

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

Change memory to storage so balance can be saved permanently.

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

mrk · November 29, 2020, 5:44pm

pragma solidity 0.5.1;
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;
}

}

CC123 · November 30, 2020, 8:09pm

pragma solidity 0.5.1;
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] = User(id, balance);
     //user.balance = balance;
}

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

}