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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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1answer
17 views

How to check if a mapping has not been written yet?

I have this mapping: mapping (uint256 => string ) private storedData; I am trying to do this: modifier dataNotStored(uint256 _index) { require( keccak256(abi.encodePacked(storedData[...
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Accessing a storage array is causing my contract to revert with no explanation

I have the following contract: // Inspired by https://fravoll.github.io/solidity-patterns/eternal_storage.html pragma solidity ^0.5.8; import "./lib/Ownable.sol"; import "./MemberStruct.sol"; ...
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Efficient way to save and retrieve hash in blockchain

I am learning Ethereum using Geth. I have a private blockchain and I am saving hashes through a REST API (python web service). I have readed I can save hash values using maps (mapping data type) and ...
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28 views

How to check if key exists in array of bytes? [duplicate]

I have an array of bytes10 inside a mapping, like this: mapping(uint => bytes10[]) public Players; I want to check if a certain index exists in the bytes10 array. I tried to check it with ....
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1answer
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How to get a nested map value from web3.js?

In contract: mapping (address => mapping (address => uint256)) public spentLimit; How to retrieve spentLimit[a][b] for given a and b from web3.js?
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1answer
30 views

Storing multiple values in one key mapping (Solidity)

Can I store multiple values in one key mapping in solidity? like I can retrieve all of the values if I use that one mapping key? Is this possible?
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1answer
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arrays and structs for function arguments

A lot of contracts and libraries with functions that use arrays and structs for arguments. Structs can themselves include arrays, structs and mappings. For example: function doSomething(MyStruct ...
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1answer
8 views

Can you have an array of mappings? The mappings have an address key and a struct value

Can you have an array of mappings? I want to have mappings with addresses as keys and structs as the value. I want to store these addresses in an array and iterate through them. so far it looks like ...
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1answer
23 views

Passing of a struct array from called contract to calling contract

I am currently developing a dAPP and I am splitting it in 2 distinct contracts. I will be calling functions from contract A to contract B. In contract B I have an array of struct which I can ...
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1answer
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Passing array of struct as parameter: Only libraries are allowed to use the mapping type in public or external functions

I am trying to push multiple items to the array of structs in the contract. Couldn't find a clear answer if it is possible to pass an array of struct as a parameter. Apparently I can't but I get a ...
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1answer
50 views

How to use array of arrays with mapping in Solidity

I'm developing a smart contract handling document signing. Mainly, there are two things to consider 1) Signers 2) Sign Types. 1) Signers: Mandatory sign the document 2) Types: Types of signs such as ...
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2answers
34 views

loop though all the members of a map

I need to loop though all of the members of a map and change their property (which is a struct). the way i'm doing this is when adding a member to the map object also save it's address inside an ...
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2answers
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Why can't I map string with address in solidity?

I want to map names(string) with a wallet address in solidity but solidity throws an error saying that its not allowed! mapping(string => address) public users; And this is the error I get: ...
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1answer
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Need to enumerate keys of a mapping [duplicate]

I have a directed multigraph of courts "trusting" each other: struct TrustedCourt { uint256 courtId; mapping (uint256 => uint256) limits; // intercourt token => amount } ...
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1answer
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Query each struct of a Mapping vs looping getter function for front-end?

I have a mapping of structs and a counter variable to keep track of how many structs are stored in the mapping. For front-end development would you recommend to query each struct using the auto-...
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1answer
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Keeping a finite set of addresses (Solidity)

struct Data { ... } contract Court { mapping(address => Data) subcourts; } I want to keep track of a small finite set (which can be added or removed) of all keys of this mapping. What is the ...
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2answers
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Set contract storage directly at deployment

Is there a way to pre-define a contracts storage when deploying it? Say I want a mapping to be filled with 1000 entries but want to avoid having to pay gas for adding every entry on its own. Since ...
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1answer
25 views

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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1answer
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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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1answer
75 views

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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1answer
78 views

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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1answer
21 views

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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1answer
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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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1answer
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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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1answer
31 views

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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1answer
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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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3answers
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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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1answer
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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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1answer
160 views

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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1answer
44 views

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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1answer
160 views

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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1answer
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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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2answers
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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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1answer
56 views

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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1answer
22 views

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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4answers
147 views

mapping one id to multiple addresses

Suppose I have a product with a specific id for sale(so I am the owner) and someone wants to buy the product from me. When he pays the price he will become the new owner of that product. How can I ...
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1answer
51 views

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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1answer
80 views

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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1answer
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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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1answer
15 views

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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1answer
158 views

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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2answers
258 views

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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0answers
50 views

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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2answers
556 views

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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1answer
33 views

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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3answers
413 views

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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1answer
17 views

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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1answer
306 views

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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1answer
270 views

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 ...