Questions tagged [state-variable]

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2answers
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How to call a method after a specific tx in a block

With web3, it is possible to call a method of a smart contract at a specific block : myContract.methods.methodName().call(transactionObject, blockNumber, callback) Is there a way to call it after a ...
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0answers
16 views

Maximum Number of State Variables

My Solidity linter warns me if I have more than 15 variables declared, and I got around this by packing multivariable into an array, such as changing unit public x1; unit public x2; into unit[2] ...
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0answers
13 views

How to find value of non-public state variable

I understand that public state variables automatically creates a getter function when deployed, its value can be accessed via the getter function. However, if a state variable is not public, how can ...
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2answers
39 views

Getter function for public variables

Many token contracts have unrestricted getter functions for state variables, which seems redundant (eg, see OpenZepplin's ERC20 contract). For example, a contract could have it this way: uint private ...
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1answer
19 views

Accessing dynamic variable name - external contract

Contract A wants to call an external contract B/C/D/E/F but the variable name is different within each contract B/C/D/E/F, and contract A does not know the variable name for B/C/D/E/F at the start. ---...
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1answer
22 views

What if millions of records to be fetched from blockchain?

This is just a hypothetical scenario. Let's suppose someone saved million of information in blockchain with huge gas consumption so far. As for reading data in ethereum smart-contract cost no gas. ...
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0answers
17 views

The code is not returning the value of x? [duplicate]

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

State Variables: What are they and how to create them?

I am new to ethereum and Solidity. I thought state variables are supposed to retain their value between calls. In the Solidity documentation, in the section State Variables, it says that state ...
0
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0answers
38 views

if “address public x = tx.origin”, why does “require (tx.origin == x”) work and "require (tx.origin==tx.origin) not

Below is a contract that i have commented on, hoping to understand the logic of the arguments. Below in bold is the question in question. The .sol currently works fine. pragma solidity ^0.5.11; ...
1
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1answer
36 views

Receiving error while getting state variable value after using selfdestruct method “Error: Returned values aren't valid, did it run Out of Gas?”

I am using selfdestruct method and passing the payable address to it but receiving the following error when trying to get the value of a state variable : "Error: Returned values aren't valid, did it ...
2
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1answer
355 views

What is the immutable keyword in Solidity?

What is the immutable keyword in Solidity and how do I use it?
0
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1answer
38 views

Length of state array is not changeable in Solidity

Consider there are 3 contracts: BankA, customer, and BankB.BankA transfers some ethers to customer and after that some customer's state variables must be changed (in a better words be updated). It ...
0
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1answer
34 views

How Solidity field variable update is happening?

I am curious to know about, how the updation of field variables in solidity is happening ?. Whether world state is maintaining for each variable in the contract as like account balance?. And one more ...
1
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1answer
36 views

Why OpenZepplin always use private visibility for state variables?

Why OpenZepplin always use private visibility with getter functions for its state variables? I can't find a reason why they are not using public, is there any potential security or gas cost difference ...
1
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0answers
32 views

Retrieving a State_object value on go-ethereum

I have a deployed contract address and I need to query a contract storage value, a token account balance that is stored on a mapping variable: mapping (address => uint256) balances; From go-...
0
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1answer
157 views

Why string variable must be memory from solidity v5.0?

May someone explain me why exactly string variable must be memory from solidity v5.0 and what does tha mean? Thanks for your help.
-1
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2answers
162 views

Truffle uint test script not updating storage variable, and strange behaviour

while testing I got a strange behavior of truffle, please see the subject smart contract code first uint256 public burningRatePercent = 50; function onlyOwnerSetBurningRate(uint256 ...
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2answers
154 views

Accessing private variables using assembly

I would like program an oracle service which I would like to charge a fee for. Therefore, I would store the data of interest as a private variable in my oracle contract. This private variable should ...
2
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1answer
22 views

defining storage literals in Solidity

I am trying to write unit tests on functions that take in a storage reference as parameters. There is not much great documentation around how to create literals for these types. These include: address ...
2
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2answers
243 views

state variable value not changing

I have very simple solidity code as below - pragma solidity ^0.5.6; contract SaveData { uint public salary; function setSalary(uint input) public { salary=input; } function ...
1
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1answer
48 views

Does a storage array have a unique address on the block-chain?

The question in the title is a little vague, so I will try to explain here. Suppose I have a contract with a storage array: pragma solidity 0.4.24; contract MyContract { uint256[10] public ...
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1answer
142 views

dApp Tech Stack

So I'm looking into building a dApp with standard app I functionality like user login/posts/likes/comments etc. Along with harnessing the power of ethereum to support betting and donations. Here is ...
2
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1answer
530 views

How State variable are stored and updated?

The Smart contract and the state variables are stored in the blockchain, let us say during deployment of a smart contract the state variable and smart contracts are stored in the block 1, and in ...
1
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1answer
128 views

Are constant state variables cached in the EVM?

From the docs: constant for state variables: Disallows assignment (except initialisation), does not occupy storage slot. Does this mean that the EVM caches constants across all contracts using ...
1
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1answer
51 views

Accessing the Ethereum State Variables using web3js (Java Script)

I'm trying to run the below code to get the state variables using the getIdBytes method of the Smart Contract, and assign it to a java script array variable, but it doesn't seem to work. All I can ...
5
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1answer
347 views

What are 'payable' state variables?

https://solidity.readthedocs.io/en/latest/solidity-by-example.html#simple-open-auction pragma solidity ^0.4.22; contract SimpleAuction { address payable public beneficiary; What exactly does ...
0
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1answer
16 views

Setting Contract level variables

I'm a Python Developer jumping into Solidity and I feel like I'm missing something about variables and scope. How do I set and access variables outside of a function's scope? I can't seem to add ...
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2answers
246 views

Abi to call value

how to calculate ABI to call some variable in contract? for example contract X { uint data; function Y(uint a) {} } How to calculate signature to call variable "data" ? I know to call ...
3
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1answer
1k views

What does “_” mean before a variable name?

I'm a beginner, just recently started reading the docs for Solidity. I can't seem to find this anywhere on google. What does the underscore mean when placed with the indexed keyword? Examples: _from ...
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0answers
30 views

Best way to restore historical storage state

What is the best way to get historical storage state, given db with current world state and blockchain data? Do I need to reverse assemby code or can I do this using receipt logs?
0
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2answers
337 views

In solidity smart contracts how do you access internal state variables declared in the constructor?

I'm working with a solidity contract that declares a state variable in the constructor like this this: constructor( address vault, address proxy ) public MarginAdmin() { state ...
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0answers
49 views

Can we issue a token with specific local state?

Will it be possible to create an ERC20-Token, that will be "minted" with specific local state on a per token-basis while this state can change over time through the execution of a method in the smart ...
2
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1answer
488 views

Why public variables aren't able to implement interface functions?

I'm curious why interfaces don't accept public variables as implementations, since public variables have getter functions generated for them. For example why couldn't the ERC20 balanceOf interface ...
1
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1answer
120 views

Why standard tokens manually create getters for balanceOf and totalSupply [duplicate]

I've been reading through different implementations of ERC20 tokens and I noticed that many of them define balanceOf[address] as balances[address] and then create a public getter() to match the ...
0
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2answers
943 views

How do I see the value of a string stored in a private variable? [duplicate]

I have read many times that sensitive data should never be stored in a transaction, but, specifically, how would the value of a state variable be read if marked private?
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0answers
174 views

How to interact with a smart contract to change a variable state

How do I change a variable in a smartcontract (bool) As requested, a new followup question from the above^ about ethereum smart contracts (solidity) If I have, early in the contract: bool public ...
2
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1answer
323 views

local var inside a function modifies another state variable

I have this very simple contract: pragma solidity ^0.4.18; contract C{ uint public a = 9; uint[] public data; function f(uint _a) public{ a = _a; uint[] y; ...
1
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1answer
106 views

Why would data be passed into a contract constructor rather than just hardcoding it, which would be less costly?

Doesn't it cost more to pass in variable assignment via a constructor due to changing state? Wouldn't it be cheaper to just assign them in the code? I am wondering if there are advantages to using ...
1
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1answer
861 views

Why do some variables' names end in underscore?

On Open Zeppelin's ERC20 BasicToken contract the variable totalSupply_ follows a naming convention I haven't seen before. Is that to differentiate it from the function totalSupply() below or is there ...
0
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1answer
282 views

Reading variables from web3 (Documentation is out of date)

I'm trying to read an ownersNum public uint from my contract. I instantiate in node: l = console.log; var web3 = new Web3(new Web3.providers.HttpProvider("http://localhost:8545")); let c = new web3....
0
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1answer
443 views

Calling a state-changing function via web3

I am trying to call a function which changes the length of a global storage array. At first I thought that the problem was related to the array-length changing attempt. But I have finally come to ...
0
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1answer
66 views

Unable to change the length of a global 2D storage array

I am facing difficulties changing the length of a global 2D storage array. It seems to be working correctly on Remix IDE, but when I try to test it on ganache-cli (formerly known as testrpc) - either ...
1
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1answer
37 views

What is the length of an empty fixed sized array?

Let's say we initialize a state variable as: uint[10] public fixed_array; This is a fixed sized array which is currently empty. What would fixed_array.length return? 0 or 10?
1
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1answer
475 views

Access previous state

Let's say I have a uint public myvar in my contract that is initialized to some value. Then, myvar gets set to 3 in the next block. How can I retrieve the old value? Is this possible with web3? ...
0
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1answer
278 views

I cant get the value of a state variable public

I am developing a smart contract which I have two contracts(A and B). I have an array variable in A and fill it with values but when I get that variable from B, the array address is empty. pragma ...
3
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4answers
570 views

Conceptualizing smart contract variables

I'm having trouble figuring out how variables are stored on the block chain. How can a smart contract be immutable and have global variables that can change? Just say I a simple contract like below......
2
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2answers
106 views

Is Solidity creating an implicit getter for a nested contract that is created?

Is Solidity creating an implicit getter or not for a nested contract that is created? Example: contract Foo { .... } contract Bar { Foo public foo; Bar() { foo = new Foo(); } ...
3
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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 ...
7
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3answers
4k views

How to get the cost (in gas) of the non-constant function call?

In my understanding, there are some situations, where the compiler can't calculate, how much Gas it takes to complete the function call. The most obvious example - when your function is calling some ...
11
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2answers
8k views

Local variable and state variable, and the difference between them

I am new to solidity. When I read the solidity documentation, it says local variable and state variable. But I can't find the definition of the two terms. Can anyone explain the meaning of local ...