Questions tagged [state-variable]

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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 ...
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1answer
346 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; ...
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1answer
166 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 ...
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1answer
1k 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 ...
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1answer
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Reading variables from web3 (Documentation is out of date)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....
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1answer
536 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 ...
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1answer
68 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 ...
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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?
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1answer
577 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? ...
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1answer
306 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 ...
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4answers
698 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......
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2answers
128 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(); } ...
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2answers
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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 ...
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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 ...
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2answers
10k 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 ...
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0answers
634 views

totalSupply in ERC20Basic contract is not initialized to zero. Does that matter?

I copied code from TenX, which copied code from OpenZeppelin. TenX and OpenZeppelin has this code for contract ERC20Basic: contract ERC20Basic { uint256 public totalSupply; function balanceOf(...
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2answers
727 views

Local storage variable

I am reading the solidity docs here and I seem to be struggling to understand the following. Data locations are important because they change how assignments behave: assignments between ...
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0answers
77 views

Layout of State Variables in Storage -> specifically NON Statically-sized variables e.g. Mapping

The following page provides information on how to access a contract's state variables, regardless of who the owner is or what methods are exposed. http://solidity.readthedocs.io/en/latest/...
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1answer
201 views

Function doesn't change change variable's value

I have made a contract with a struct, Stock. I have an array with two such Stocks. They can be initialized fine, but when I try to change the value of a variable nothing happens. Also, the same ...
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2answers
352 views

Not able to read data from smart contracts

I am doing PoC on Ethereum using Azure Ethereum network and Web3. I was working from last 1 month and I have created one smart contract for student management and that was working like fab. But for ...

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