Questions tagged [mapping]

A type in solidity that allows access to arbitrary elements via a key, similar to a dictionary or hashmap in other languages.

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Solidity. Check if key has value in mapping. Operator != not compatible with types struct

I am new to solidity. I have a Person struct and mapping: struct Person{ uint age; string gender; } Person[] players; // holds the 24 players mapping (string => Person) ...
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Solidity. How to add an address to a mapping

I have this: contract Diary { string[] private facts; mapping (address => bool) approvedAddresses; address owner; constructor() public { owner = msg.sender; ...
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How to select a wallet address by the token number he owns?

I need to allocate a winner among the token holders. I want to keep the concept that the more tokens someone buys the more chance there will be that he will be the winner. now lets say 960 tokens ...
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Vyper mapping inside a struct

Is it possible to have a mapping inside a struct for vyper? For example: struct Teddy: id: uint256 year: uint256 component: map(uint256, uint256) teddies: private(map(uint256, Teddy)) ...
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I would like to 3 mappings

I am a beginner. I would like to 3 mappings I know 2 mapping looks like this: mapping (address => mapping (address => uint256)) public allowed; and my question is: is 3 mappings look like ...
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Trouble accessing an array inside a struct inside a mapping via web3

Here are a few relevant code snippets from my smart contract struct Constituency{ uint16 id; string name; uint64[] cans; } mapping(uint => Constituency) public constituencies; ...
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TypeError: Indexed expression has to be a type, mapping or array (is function (address) view external returns (string memory,string memory…)

I have 2 contracts first one is sub second one is main . First i deploy main and create a new subtoken. Then I want to access my maincontract in subToken contract but I cant :( When I compile this ...
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How do I check If a map entry doesn't exist for a given sender?

I have a map such as: mapping (address => bytes32) private myMap; Later in the code, in a function, I want to ensure my sender already has an entry in that given map. Can I do this? require(!...
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How do mappings in solidity occupy memory

Say, I declare a mapping that uses uint256 numbers as keys and maps them to a single 8 bit character. I add 5 members to this mapping. Obviously, I can then access any of these 5 characters using ...
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Getting information from contract address?

pragma solidity ^0.5.0; import 'https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/math/SafeMath.sol'; contract SubToken{ using SafeMath for uint; struct token{ ...
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Struct creates instances with zero values for all of it properties instead of using function arguments

Inside my smart contract I have a struct type NotaryEntry and a function addNotaryEntry which creates an instance of the struct and add to a mapping, I do pass the right values to the function but the ...
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Mappings inside functions to filter query

I have a struct and several boolean mappings that are used to keep track of struct's properties struct Animal { string species; bytes32 ID; } mapping (bytes32 => Animal) public Animals; ...
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Member “name” not found or not visible after argument-dependent lookup in string storage ref

I have code like this and I want to set my name, surname and age in my struct so I want to set them and get them using with my functions here's my code : pragma solidity >=0.4.0 <0.7.0; ...
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Expected ')' but got identifier if(string name != users[name]){ ^--^

pragma solidity >=0.4.0 <0.7.0; contract NewHello{ mapping(address => string) public users; // contains a name for every address function updateUser(string memory name) public { ...
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member not found or not visible after argument-dependent lookup in mapping

pragma solidity >=0.4.0 <0.7.0; contract New{ mapping(address => string) public users; string name; address[] public userAddress ; //string[] public userNames; ...
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Type string memory is not implicitly convertible to expected type struct InsanFactory.User storage ref

pragma solidity >=0.4.0 <0.7.0; contract InsanFactory{ struct User{ string name; address myaddress; } mapping(address => User) public userStructs; ...
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How to access content of mapping in a struct?

I'm aware of this post: Accessing a mapping within a struct via Truffle console However, it seems to me, it does not provide a clear answer. Also, my question is more generic and not just for ...
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Mapping with iterating uint as identifier - multiple transactions in the same block

I want to use an iterating uint as an identifying number, but I have a simple question to make sure I can do this safely on the mainnet. Here's a simple example to demonstrate the issue: pragma ...
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Why does a mapping update itself when I am not doing anything?

The title is a little bit vague but I've seen this contract and tried it on remix: pragma solidity ^0.4.24; contract Tester { struct Account { uint256 balance; } mapping (address => ...
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Can I init mapping in solidity with pre-defined values?

f.e in Python: mappingName = { 'key1': 'value1', 'key2': 'value2' } What are the best practices to achieve that?
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How can I push data to array when using mapping (address => address[]) mappingName?

What is the exact syntax to push data using the above given syntax?
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What is the maximum storage size to store number of addresses in array? [duplicate]

I want to map multiple addresses using one address by doing this: mapping (address => arrayOfAddresses[]) mappingName; What is the maximum size of addresses I can store in that array?
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map multikey how-to?

I'm trying to create a map whose key is composed of two bytes32 keys. I've tried with tuples-keys and struct-keys but both are rejected by the compiler. I'm also thinking about "hashing" both keys ...
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Problem on returning fields of a struct inside a mapping

I have the above code mapping(string => Owner) public Owners; function addOwner( string memory name, string memory surname, string memory fathername, string memory mothername, string memory ...
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DeclarationError: identifier not found or not unique 'candidate'

I got the above error at the mapping 'candidate' pragma solidity ^0.4.22; contract Election { struct Candidates { string name; uint voteCount; } struct voter { bool authorized; ...
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Reset all values in a mapping

I am trying to figure out how to have the balance of all players reset to (amount) when a certain condition happens. This is the function that will update a specific player balance. How do I make it ...
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Best way to support restoring of all the keys of a mapping

I have a contract, in which I maintain the keys of a mapping in two different ways: Storing each key in an array Emitting an event for each key I do this in order to be able to restore the keys (and ...
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Default getter and setter for mapping in solidity

In my smart contract I've public mapping as mapping (uint=>User) public users where User is a Struct, so is there any way to get the values of this mapping using default getter. For Example : If ...
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Mapping or indexed event

I want to store data on chain that is not needed within a smart contract but should be retrieved easily and particularly quickly from outside. I know that storing the data within an indexed event is ...
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how do I loop through a mapping of address [duplicate]

I have a mapping of list of struct (mapping (address => struct[])) I'm having a trouble in how to display all them together in the front end (i'm using React js). Thnx.
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Use Values Returned from One Function in Another

need a little help if you can spare the time. Making a little card game where people can collect "warrior" cards. We'll have an initial 12 master "cards" that supply the initial traits for the ...
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In Ethereum how to check if in mapping, the key already exists?

In this Proof of existence, integrity, and ownership contract of a file why files[fileHash].timestamp == 0 is used? why timestamp? contract Proof { struct FileDetails { uint timestamp; ...
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How to search through blockchain?

I m doing project for document verification using blockchain in which we don't have to carry documents everywhere, hash key of block will fetch data of doc from blockchain.I m not getting how to ...
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access mapping inside mapping of struct in Solidity ^0.5.0

I have a contract which looks like this: contract a { struct Str { uint256 totalTokens; mapping(address => uint256) playerTokens; } mapping(uint256 => Str) public ...
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How Ethereum stores its data in the blockchain [duplicate]

I am new to ethereum and the blockchain, but I am wondering about blockchain databases. Mainly I am wondering how exactly the database data and the blockchain merge. For instance, in a database you ...
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Associate event struct to user addresses

I have two contracts. One called User and other called Event pragma solidity ^0.4.24; contract User { mapping(uint=>address) addresses; uint addressRegistryCount; } pragma solidity ^...
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Return a mapping in a getAll function

pragma solidity ^0.4.24; contract User { mapping(uint=>address) addresses; uint addressRegistryCount; function set(address userAddress) public { addresses[...
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How do I get product/parcelID from particular Assigned address using struct and mapping?

struct Sellers{ address sellerAddress; uint parcelId; uint parcelPrice; } In this struct I've entered multiple parcel Ids to sellerAddress and I've retreived them using _sellerAddress. ...
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Struct and Mapping input value error of Invalid Opcode while calling setSeller() to store multiple seller's addresses

What dose the -1 means? Or why we should use -1 while pushing one element in array. What should I enter in sellerAccounts: field as input? pragma solidity ^0.5.1; contract Seller{ struct ...
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Return an array of adresses

I have a mapping with the key as an address and the value as an array of addresses. How do I return the array of addresses? In older solidity versions it works. In newer compiler versions I have to ...
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Pure functions as a replacement of constant mappings?

I need to create a lookup table [uint -> uint] that is constant. Constant mappings or switch-case are not available in solidity. Are pure functions full of if-else the only option? Any better ...
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Why was mapping introduced in Solidity instead of a dictionary or map data strcuture?

What was the thought process behind introducing mapping in Solidity? Doesn't dictionary and map serve the same purpose in other languages? I want to know the necessity that led to the inclusion of ...
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How to access nested struct values?

I'm new in solidity programming so for learning purpose I'm developing e-voting system using ethereum blockchain. Code mentioned below, pragma solidity 0.4.25; contract RegisterCandidate { // ...
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Which is the expected behavior trying to get an undefined mapping value?

In ERC20 standard, _allowed is defined as: mapping (address => mapping (address => uint256)) private _allowed; and the getter function is defined as: function allowance(address owner, address ...
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How do I read an array inside of a struct?

as part of learning solidity and smart-contract development, I am developing a simple part management/tracking system. I have a struct and a mapping for a list of parts as such: struct Part { uint ...
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Possible ERC-20 improvement: Token-specific ENS equivalent

With ENS still providing quite a difficult user experience for the average user, I'm wondering why standards like ERC-20 don't implement a simple mapping allowing people to set names equivalent to ...
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Is There any way to check if the entered key is having a corresponding value in a mapping or not?

Suppose In a banking system many people are enrolled (managed through mapping ) mapping (address => bool) enrolled; And only those can deposit who are enrolled in the bank. Can I check if ...
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How to initialize a new struct with an empty mapping? [duplicate]

For expl. mapping(uint => Test) tests; struct Test { uint id; mapping(address => uint) votes; } function newTest() public { test[0] = Test(0, <EMPTY_MAPPING>) }
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Return an array of mappings reflecting global state between struct associations?

I am looking for a construct that's something like "return an list of key value pairs," which I think would be implemented as an array of mappings. Is that right? That is, I'd like a data structure ...
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Is there a form of mapping with an even larger space?

I understand from here that the space for mapping() is drawn from a size of 2^256 * 32 bytes storage, which provides a 1 chance in 10^69 of overwrites. If I'm working with contracts on the order of ...