A type in solidity that allows access to arbitrary elements via a key, similar to a dictionary or hashmap in other languages.
Questions tagged [mapping]
522 questions
5
votes
1 answer
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;
string owner;
}
mapping (string =>…
Yash Shukla
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2
votes
0 answers
Tuple as mapping key?
Can we use tuple as mapping keys? For example:
mapping ((address, uint256) => uint256) myMapping;
If not, what's the closest workaround? Consider the two components of the tuple can go up to uint16.
EDIT
To be more explicit, I can think of two…
Roy
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2
votes
0 answers
Why can mappings not be used as parameters or return values of public functions?
The solidity docs say this about mappings, but don't give a reason why:
Mappings can only have a data location of storage and thus are allowed for state variables, as storage reference types in functions, or as parameters for library functions.…
pastacompany
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0
votes
1 answer
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;
bool voted;
uint vote;
}
address…
chuks
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0
votes
1 answer
How can I add an element to a mapping array (mapping[])?
Remix accepts the following code and allows me to deploy the contract:
pragma solidity 0.4.24;
contract bytes32array {
mapping(address => uint)[] balances;
function addBalance(address _address, uint _index, uint _amount) public…
CreatedAMadman
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0
votes
1 answer
Sha256 Digest Mapping to Address
Sha256 Message Digests are 32 bytes, however they are typically expressed as a 64 character string. Is it possible to map the string to an address?
Something like
mapping (stringToBytes32(bytes32) => address) public digestToAddress;
I'd rather…
0
votes
1 answer
Mapping: Does the length of the key as string affects the gas usage?
I am using string as a key on mapping data structure.
[Q] While we are use mapping, when the length of the key string increases, does it also increase the gas usage?
mapping(string => int) map;
contract.array("mykey"); …
alper
- 8,395
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0
votes
1 answer
Nested mapping in solidity
this code require two input(_Id,_name) to get age
i need to get name and age from input id only
// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.7.0 <0.9.0;
contract nestmap
{
mapping(uint256=>mapping(string=>uint256)) public User;
…
0
votes
1 answer
Mapping both ways
if I want to have a mapping both ways (getting value by key and key by value) is it the most efficient approach to simply initialize 2 mappings pointing in the opposite directions?
mapping(uint64 => address) public frontEndTags;
mapping(address =>…
Jan Beneš
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0
votes
2 answers
How does `mapping(address => uint) public balances` get balances?
I noticed that balances as a mapping
mapping(address => uint) public balances;
and acts as a dictionary where addresses are mapped to balances.(address -> balance). For a typical dictionary to do so, we need to first provide/initialise the…
Pe Dro
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0
votes
1 answer
How to store large amount of addresses
I was looking into how to store large amount of addreses for example to adding atributes to different token holders.
As far as i know, most people use mapping, i was researching how that works but the only information i could find was "You can think…
