Questions tagged [storage]

all questions regarding data and storage on the ethereum blockchain

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Issues with extreme large solidity mapping

Is there any scalability problem if the number of items of a solidity mapping increase too much? For example, any problem when adding, changing or removing some item in the dataset? Or any other ...
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If I pass an enum as a parameter does it get stored in the blockchain?

I'm developing a Rock/Paper/Scissors Smart Contract (with a Commit-Reveal scheme). I have this enum: enum Move {rock, paper, scissors} I want to pass it to a function, without storing it to the ...
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Why do you always have to declare the “memory” keyword for strings inside a function? [duplicate]

Example: function myfunc (string memory words) public returns (string memory) { XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX } Why is it compulsory to declare the "memory" keyword? Would the ...
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16 views

In Solidity, Modifiers & Mapping variable are stored where - storage or memory?

In Solidity, Modifiers & Mapping variable are stored where - storage or memory ?
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1answer
29 views

Is there any way to find out what exchange a ETH wallet was created?

I added a ETH wallet address to Genesis Mining back in 2017 for a 2 year contract. After the contract was finished it still took them a year to add the ETH to said Wallet. (long story but I did not ...
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How many key-value entries can be stored in Solidity Mapping data structure?

mapping(uint => uint) public myMap; function store(uint key, uint val) public { myMap[key]=val; } function retrieve(uint key) public view returns (uint){ return myMap[key]; } Considering ...
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1answer
19 views

Where is the data of a transaction saved?

To introduce my question I would like to give an example. Suppose a customer wants to join a gym. A transaction is sent and contains: customer id name and surname start date end date The smart ...
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23 views

How to initialize storage for smart contracts in the genesis block

I have a simple smart contract that will be added as part of genesis block. Need to initialize the field "message" with default value as constructor is not executed as part of genesis block ...
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1answer
36 views

Do parts of decentralised apps take advantage of centralisation?

So, obviously MetaMask interacts with public, distributed ledgers in order to show my balances, however, from a technical perspective, do certain parts of the application use centralised databases? ...
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23 views

How store memory array in storage

In this code, I want to send an array of bytes32 and store them in the struct but I get the error which is TypeError: Type string memory[8] memory is not implicitly convertible to expected type ...
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26 views

Does delegatecall() use only the calling function?

Let me explain with the code: contract A { function f() public { [...] g(); } function g() private { [...] } } contract B { A a; function delegateA() public { (bool success, ) = address(...
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29 views

Ethereum Smart Contract Storage

I'm currently creating my first dApp, and have some trouble understanding the storage of data of smart contract on the Ethereum blockchain. I've altered the react basic code by adding a constructor. ...
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How to store array parameter of a function to contract state?

I am trying to save an invoice to contract storage (see function addNewInvoice(..)) but I seem to be tripping over the data locations. // SPDX-License-Identifier: private pragma solidity >=0.7.0; ...
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1answer
52 views

Gas cost of setting a state-variable to the same value

According to this spec, setting a state-variable to the same value consumes 200 gas. However, I conducted a test over ganache-core v2.10.2, and the result was closer to 800 gas: Solidity Contract: ...
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52 views

Solidity Encoding Function Call With A Reference Parameter

I'm deploying an external library. This library will have a function that modifies a state variable of the calling contract. I am accessing this library through a proxy contract that stores state. So, ...
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17 views

Storage vs Memory in the context of Gas Cost

I have two snippets -- one using memory, the other referencing storage: function winnerName() public view returns (string memory winnerName_) { string memory winnerName_ = ...
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1answer
62 views

Storage Address of Smart Contract Variables

I need to know storage address of solidity smart contract variables before its deployment. how can I get this?
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1answer
53 views

Clarification on how Calldata persists on the blockchain and how Optimistic Rollups use it

So I see that a lot of optimistic rollup solutions say that they store the chain's transaction data on Ethereum via "calldata" which is way cheaper in gas costs than contract storage (I ...
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18 views

Storing Struct inside an array. Help Please

I am designing an EHR System that will store patient records (with a unique ID) and separated by the date and Hospital entered. I am able to enter data in Hospital struct mapping to the Record struct, ...
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22 views

Making sure a string (input/output) is less then 64 characters

I'm working though some basic solidity tutorials using remix. I'm having trouble with the concept that there is no way to edit a string built into the language. In other programing languages I would ...
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1answer
94 views

How to get data location for string > 31 length

The documentation says: bytes and string are encoded identically. For byte arrays that store data which is 32 or more bytes long, the main slot stores length * 2 + 1 and the data is stored as usual ...
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18 views

Performance of Dapps when millions of records to be fetched

I am thinking of Dapp with react js and ethereum. Using IPFS for data storage. Let's assume that blockchain holds millions of hash addresses from IPFS. I need to show those millions of records and ...
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111 views

Type struct Mycontract.User memory is not implicitly convertible to expected type struct Mycontract.User storage pointer

pragma solidity >=0.5.0 <0.7.0; contract Mycontract{ uint256 a; struct User { string name; } User[] users; function foo() public{ **User storage user=User("hey&...
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1answer
29 views

The below code gets compiled but when foo is called invalid opcode error is thrown

pragma solidity >=0.5.0 <0.7.0; contract Mycontract{ uint256 a; struct User { string name; } User[] users; function foo() public{ User storage user=users[0]; ...
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1answer
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Ethereum Smartcontracts with YottaChain

I am very much curious about this new storage system YottaChain. Can someone point me good articles/videos/sources as a reference to go through and understand its implementation with ethereum smart-...
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1answer
25 views

why x(function setArr) is not being returned?

pragma solidity >=0.5.0 <0.7.0; contract Example{ uint256[3] x; function setArr(uint256[3] memory y) public returns(uint256[3] memory){ x=y; return getArr(x); } ...
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1answer
21 views

Understanding data location

pragma solidity ^0.5.16; contract mycontract{ uint256 public a; function foo(string calldata _name) external { string memory names; names = _name; getname(names); ...
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1answer
28 views

DeclarationError: Uninitialized storage pointer. Struct error when running truffle tests

I've seen other similar questions but they don't explain why this error happens and/or they are case specific questions. So, I have this code: pragma solidity >=0.4.22 <0.7.0; contract ...
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1answer
141 views

DApp Development- how to update dapp and keep existing data

Compare to web application that separate the application and database, we can update the application and keep the existing data. Could you suggest me how to update dapp and keep the existing data?
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1answer
76 views

Issue with dynamic matrices in solidity

I have a matrix in solidity like that string x[][] I'm trying to write functions to return rows and colums The following code works well: // SPDX-License-Identifier: unlicensed pragma solidity ^0.6.0; ...
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1answer
22 views

When using mapping, why use an address over bytes32?

From an end user standpoint, they will never want to use the address for searching for mapped data when they could just submit a username for function parameters, so is there any specific reason why ...
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Data storage : mapping vs sub contract deployment

I read over few website, tutorials and answered question here on SE. There is a huge warning about deploying new contract just to store datas. i.e. : bad uint256 public amount; bool public isAdmin;...
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1answer
32 views

Passing storage of one library to another library

I have two libraries: A and B as well as contract C using them. Library B, in one of its functions, needs to call a couple of functions defined for A.Storage. The code below compiles, tests are ...
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66 views

Storing data directly on chain

Im trying to store data directly on the blockchain, not on a smartcountract as they have a limit of what they can handle and it would slow down the chain to go above the limit. My initial plan is to ...
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1answer
39 views

Mapping didn't storing unique values

I wrote this piece of code with the goal to store unique documents hash. Used mapping to accomplished that. pragma solidity ^0.5.16; contract DocumentHash{ string public documentHash; ...
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1answer
53 views

How does Smart-contract's storage works?

I keep hearing that for each contract there is a storage as contiguous array (to have constant O(1) lookup) with 2^256 slots, 32 byte each, available. But it cannot physically be true. How is it ...
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1answer
77 views

How can I make an off-chain call to get the data stored at a specific storage slot on-chain? [duplicate]

I want to get data from on-chain that is not explicitly available through a getter. For example, if I know that there is data at position ...
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1answer
324 views

Nested Structs with Mappings Inside

I have the following code: // SPDX-License-Identifier: MIT pragma solidity >=0.4.22 <0.7.0; pragma experimental ABIEncoderV2; contract VenueRegistry{ struct Queue{ uint head; ...
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47 views

ERC20 balance Storage Address key - how to tell which key belongs to which wallet address

I am trying to derive changes of account storage by mapping accounts (here, the accounts represent the key address in the ERC20 balances mapping mapping(address => uint256)) to their corresponding ...
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1answer
18 views

Is data copied or referenced from local storage to global storage?

For example, when a struct is initialised to storage in a function, then assigned to a global state variable such as an array or mapping type, does the local struct get copied to the global state ...
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1answer
108 views

When and where do I set ERC721 tokens' data?

I am currently working on a smart contract to sell ERC721 tokens. I understand that my code should have a function that allows me (the owner) to mint a token and add it to a list which stores all the ...
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1answer
26 views

Is transaction history available as a part of the blockchain implementation, or do I have to implement saving token history myself

I am implementing a CryptoKitties style of ERC721 tokens, to be deployed on Ethereum. But I am not clear how to implement the transaction history of the individual token? For example all the ...
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29 views

Smart Contact to store data from XLS/CSV file

Is there any existing code/work on how to store data written in an XLS file into Ethereum (geth) using a smart contract? I am trying to publish data that is written in an XLS file onto the Ethereum ...
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15 views

How to save/read mappings within struct?

I am trying to create a mapping inside struct and then create a mapping of the struct. Take a look at below example: // ------------------------------------------------------------------------ ...
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1answer
40 views

Is it cheaper overall to store a keccak hash or to store a ripemd(keccak) hash?

As titled. I'm learning to build a DApp and I'm wondering if it's worth it to add the extra RIPEMD layer over keccak for a shorter hash to reduce storage costs.
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2answers
34 views

Set and delete storage variable in same tx

I did some poking around and didn't see an answer... and I figure someone knows this off the top of their head. Question: what is the gas cost associated with setting and deleting a storage variable ...
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24 views

How do I determine the data storage structure that corresponds to a specific storage address?

My goal is to understand the details of the 1st bZx exploit. I am using the State Changes section of Etherscan to help me accomplish this. Some state changes affect the storage of certain data ...
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Why Does Ethereum Not Support A Native (Non Smart Contract) Form Of Multi-Sig? [duplicate]

After becoming a victim of exchange fraud and witnessing how it negatively impacted the lives of hundreds of others, I'm currently undergoing a study of all the past cryptocurrency exchange hack/fraud ...
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3answers
181 views

Can the mapping storage change after contract deployment?

I am beginner in mapping.I work on Truffle and Ganache. I deploy the following contract: pragma solidity ^0.5.12; contract customerFinder{ mapping(uint256 => address payable) public ...
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1answer
226 views

Searching for a value in a dynamic array

I understand that for loops on dynamic arrays are a big no no in Solidity, so I am trying to find an alternative to this problem. Goal: From a dynamic array of numbers, I am trying to extract the ...

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