Questions tagged [data-types]
The data-types tag has no usage guidance.
60
questions
3
votes
1answer
19 views
Can I add an int32 to an int256?
I'm trying to reduce the storage size of my contracts by reducing the bytes required to store my int data types (among other things).
Can I get the best practice for adding int256 and other smaller ...
0
votes
1answer
23 views
Does it make sense to require token value to be anything but negative to prevent hack (more details below…)?
I was asked to validate a smart contract for a token and a function that puzzled me looks like that:
function transferFrom(address _from, address _to, uint tokens)
{
require(...
1
vote
1answer
24 views
Why use anything but uint256/int256 outside of a struct?
I see how uint8 can save space within a struct, but outside of that I do not see any reason to use anything but uint256. The gas cost is slightly higher for uint8. The only reason I can think of is ...
2
votes
1answer
41 views
How are we able to send 512 bit hash as a bytes32 variable?
I have a code that is working:
solidity
function checkSignature(bytes32 h, uint8 v, bytes32 r, bytes32 s) public pure returns (address signer) {
bytes memory prefix = "\x19Ethereum Signed ...
1
vote
1answer
30 views
is there a list type in solidity?
I know there are dynamically sized arrays, but I need a data structure that can remove elements from the middle cheaply. Using pop() with a dynamically sized array should require a shift of every ...
0
votes
1answer
123 views
Solidity, problem with bytes decoding
back with another question towards solidity Guru's. I am trying to call a method which takes bytes array as an input, but either I am encoding this parameter wrongly or decoding it wrongly. Solidity ...
4
votes
2answers
823 views
Solidity! Invalid implicit conversion from string memory to bytes memory requested
pragma solidity ^0.5
contract ProofOfExistence {
// ... some code here
function proofFor(string memory document) public view returns(bytes32) {
return sha256(document);
}
//...
2
votes
1answer
42 views
Understanding first evm word of reference types in assembly
Given the following function:
function getArrayItems(bytes calldata) external returns (
bytes4 _signature,
bytes32 _wutIsThis,
bytes32 _length,
bytes32 _firstItem
) {
assembly {
...
2
votes
2answers
26 views
Validate bytes16 argument size
I have a function which accepts one bytes16 argument.
function start(
bytes16 reference
)
I have some events which I use to track behaviour, using reference as the index. Everything works ...
1
vote
0answers
169 views
How to decode Tx data? Online tool?
Is there a fast way to decode the data returning from a Smart Contract call? I know there are github projects with JS libraries to decode this kind of data (such as https://github.com/ConsenSys/abi-...
asked Jan 23 '19 at 9:28
Juan Ignacio Pérez Sacristán
2,7433 gold badges24 silver badges57 bronze badges
2
votes
1answer
591 views
I want to compare hash that I have passed in the argument of the function but keep getting this error
function compare(string memory input, uint _y) public returns (uint){
bytes32 hashedinput = keccak256(input);
}
Error: Invalid type for argument in function call. Invalid implicit conversion from ...
15
votes
2answers
5k views
What's the difference between 'address' and 'address payable'?
I saw a Solidity smart contract where some variables were declared with the type address and some were declared with the type address payable. What are the differences between the two?
Do they store ...
1
vote
1answer
45 views
Solidity, push overrides array [duplicate]
pragma solidity 0.4.24;
contract ArraysExample {
uint[] numbers;
function addUser() public returns (uint[]) {
numbers.push(random());
return numbers;
}
function random() ...
2
votes
1answer
231 views
How to convert string to type defined by an abi.Type for payload construction?
I am writing a CLI in Go that should faciliate users to be able to make contract function calls from it. This entails generating contract ABIs and providing input parameters to the function arguments ...
1
vote
1answer
73 views
Gas cost difference between uint[] and mapping(uint => uint)
When mapping for example a large integer to some integer,
uint[] index;
index.length = 1000000;
index[600001] = 4;
is it cheaper to use
mapping(uint => uint) index;
index[600001] = 4;
? one ...
0
votes
1answer
21 views
Membership in a set of strings
I'm looking solidity help in storing a set of strings and checking for membership in that set. I have a concrete and an abstract question on that:
Concrete
What is the data structure in solidity ...
1
vote
2answers
63 views
Thinking through from traditional DB to ETH
I am looking for a data structure kind of like this:
[
"data": {
"id": 0,
"hash" : "5feceb66ffc86f38d952786c6d696c79c2dbc239dd4e91b46729d73a27fb57e9",
"owner" : 0,
"status" : "...
2
votes
2answers
2k views
address payable type - store address and send later using Solidity 0.5.0
Solidity 0.5.0 has separated the "address" type into two types: address payable and address. Only address payable have the address.transfer method. I don't want to use the withdrawal mechanism.
When ...
0
votes
1answer
63 views
2d array of different types?
I got quite an interesting question.
I have created an array of structs, and in each struct, I have an array of address.
Then I got a method that when its called on given struct [index] its adds ...
0
votes
1answer
85 views
How to use Ethereum as a database for an order book? [closed]
I hope this question is not too general. I would like to have a few opinions.
What is the best way to work with data in Ethereum? Lets say we build a decentralized exchange on a small scale. How ...
0
votes
1answer
73 views
How to implement a data-type Range (or Interval) in Solidity
For a Smart Contract, in Solidity, we want to implement ranges.
The reason is that many interactors do so on "ranges". Our Contract holds batches of coupons which we don't need, nor want to, track ...
1
vote
1answer
84 views
Why are timestamps stored in a uint (256 bit) when they would fit in a uint64?
A (signed) 64 bit timestamp can store a date much larger than the age of the universe.
On many platforms this would be a micro-optimization, but in the context of Ethereum, we want to squeeze every ...
0
votes
1answer
364 views
true and false not the same as 1 and 0 for web3 / solidity?
When I use remix to execute a function with a bool field and I put 0 into it (which I interpret as false), the remix console output tells me "bool myBool": true (what I don't understand). So I would ...
2
votes
0answers
71 views
Plasma: how were the UTXO bitmaps conceptualised and how will they be stored?
From the white paper, page 5:
We construct an interactive game whereby the exiting party attests to
a bitmap of participants’ ledger outputs arranged in an UTXO model
which requests a ...
1
vote
0answers
74 views
how do you handle token value data type in database?
Ones who do exchange / Investment platforms development, all ERC20 tokens has its atomic unit and only moved by specifying value in its atomic form.
for eg: 1 BuritoToken with unit decimals as 18, ...
0
votes
0answers
152 views
Smart Contract - Storing 113+ byte buffer in solidity
So I am using the module (eth-ecies) in npm to perform encryption of a message offchain using the public key of my reciever, and in turn I get a 113+ byte buffer after the encryption is done. Now i ...
4
votes
1answer
2k views
Error: Operator == not compatible with types address and bytes32
How can I change the last line in the following code to make it work?
contract University {
address public owner;
address public student;
bytes32 fName;
bytes32 lName;
...
1
vote
2answers
206 views
How to type-cast a function pointer in Solidity?
I have a function that takes a parameter of type function (uint256) view returns (uint256).
I want to pass it a pointer to a function of type function (uint256) pure returns (uint256).
Obviously ...
1
vote
1answer
149 views
Compare memory pointers in Solidity
Is there a way to compare pointers in Solidity?
I have two local variables:
uint256[] memory a = new uint256[](256);
uint256[] memory b = a;
If I try a == b I get this compiler error:
TypeError: ...
2
votes
1answer
131 views
How much data can be stored in a bytes type in a smart contract?
What are some estimates of how much data can be stored in a bytes type in a smart contract?
contract test {
bytes data;
function storeData(bytes _data) {
data = _data;
}
}
0
votes
2answers
99 views
Stellar operator types compatibility issue
I have an issue creating a calculation based smart contract which performs some calculation based on some formula. Here is the function as bellows:
function financialReputation( ufixed xb , ufixed ...
0
votes
3answers
453 views
How to set rate in decimals in solidity?
I want to set my price of token sale in ICO as 1 ether=0.0111111111. Since, solidity doesn't support decimals, what is suggested way to do that?
1
vote
1answer
462 views
Add data to an array in assembly for solidity
Hi I'm trying to make a function in assembly inline with following purpose:
Given: An array in the blockchain with names (= bytes32[] _documentHashes).
Asked: Find which indexes are equal to the ...
1
vote
2answers
428 views
Recursive struct in solidity
I'm trying to implement a binary tree in solidity.
struct BTree{
uint x;
BTree lesser;
BTree greater;
bool nil;
}
Just realized that this is not possible as struct definition can't be ...
1
vote
1answer
217 views
How do I clone a struct in solidity?
I want to be able to trigger runTest() and return false. I'd need to clone the struct at some point but I'm not sure how to do it in solidity. I thought passing it to another function as memory would ...
1
vote
1answer
221 views
web3.py - Python dtype for contract function with int256[x]
Say I have this example contract:
pragma solidity ^0.4.0;
contract SEexample {
int256[3] thing;
uint8 internal i=0;
function submit(int256[3] bids,int256[3] prefs) public returns (...
0
votes
1answer
244 views
Is it possible to create structs and declare a variable?
Let's say I have a base struct, Base. I can set it up like this;
struct Base{Struct2 data}
Here Struct2 is another structure. But what if I want to create a Base struct where the data type value is ...
1
vote
1answer
15 views
Address Not Getting Stored Correctly in State Variable?
I am trying to write a contract where the originator of the contract will offer a reward that can only be claimed by a different address that she or he specifies. To do that, I am trying to create ...
7
votes
2answers
3k views
Convert bytes32 to bytes
Is there a simple way to convert bytes32 to bytes in Solidity?
I'm trying to get the length of the string passed in the bytes32 variable but everything gets returned 32 size which makes sense.
But ...
0
votes
1answer
180 views
How to check if a function has been assigned?
I want to check if the callback has been assigned to avoid the exception:
pragma solidity 0.4.20;
contract Test {
function() external callback;
function test() public {
if (/*check here ...
3
votes
1answer
72 views
How to receive a fractional number as parameter to my function?
In my Solidity smart contract, there is a function that needs to receive an amount as parameter.
This parameter is the value to be used for a transfer function. Considering the user may need to ...
3
votes
2answers
1k views
Solidity bool size in Structs
I am trying to pack tightly my structure data type.
The question that arose is how much storage size does the bool variable take?
And if we suppose that it will take 1 byte, if I put consecutive up to ...
3
votes
3answers
436 views
Storage Pattern considering Gas cost
I was following Are there well-solved and simple storage patterns for Solidity? and ended up creating Mapped Structs with Delete-enabled Index to make sure that my array doesn't grow infinitely, when ...
1
vote
2answers
464 views
Serialization of any solidity type
My initial aim was to return structure from the function.
After web search I ended up with serialization of data structure into bytes array.
Now I try to figure out how each type is represented in ...
3
votes
1answer
410 views
Any way to convert the characters that make up bytes into a string?
For example if I have a bytes4 variable that is "0xabcd1122" is there any way to turn this into a string with a value of "abcd1122"? I am asking because I want to assign a unique identifier to a token ...
1
vote
2answers
547 views
retrieving data from smart contract
I have following Solidity code:
pragma solidity ^0.4.18;
contract ContractsRegistry {
address owner;
struct ContractInfo {
bytes32 subject;
bytes32 companyName;
string contactName;
...
0
votes
1answer
1k views
string memory[3] memory is not implicitly convertible to expected type bytes32[] storage ref
I have the following (array of bytes32 types):
bytes32[] public allTokenSymbols = ["0x4554480000000000000000000000000000000000000000000000000000000000", "...
4
votes
2answers
98 views
Storing a lot of data in a contract efficiently
Do data types like arrays or maps get stored in the patricia tree
(#1)where each element (in the map) has it's own path, and when you add a new element you reference the whole sub tree and add a new ...
1
vote
1answer
70 views
How do types inherit from libraries?
When you're using a library like SafeMath, and then have using SafeMath for uint256; within a contract, how do uints know to become the a parameter of the library functions? Is that just a convention ...
3
votes
2answers
1k views
Why is uint so popular
Among every tutorial/real world example I have yet to come across anyone using the int datatype, I almost thought there wasn't one existing.. Is there a specific reason for uint's uncontested ...
