Questions tagged [memory]

Questions related to memory use in Solidity or by nodes

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13 views

Modify the state using returned variable (Array.push)

In my contact I want to have one place where I find an existing object(struct) and then use it in multiple places to read and modify it - but seems like it's not possible? contract A { struct ...
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0answers
15 views

What is an efficient way for converting 'bytes4' into 'bytes' or 'byte[4]'?

I am currently converting bytes4 into bytes like this: function convert(bytes4 x) public { bytes memory y = abi.encodeWithSelector(x); ... } Is there a more efficient way? Also, is there an ...
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1answer
64 views

When should I use calldata and when should I use memory?

I have seen people use both memory and calldata keywords when writing Solidity. Specifically, they are used when declaring function parameters. When should I use memory and when should I use calldata?...
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1answer
23 views

What is the meaning of “memory is erased between (external) function calls”?

From the official documentation on the memory keyword: The second is “memory”, this is used to hold temporary values. It is erased between (external) function calls and is cheaper to use. Can ...
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1answer
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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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What does this mean: “It is not possible to enumerate storage from within a contract” (Solidity doc)?

In the Solidity docs section on memory, you find this paragraph (emphasis added): Each account has a data area called storage, which is persistent between function calls and transactions. Storage ...
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1answer
37 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
56 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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2answers
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Where is the length of an array located in terms of memory layout?

For example, given the following cases: uint[3] memory arr; uint[] memory arr = new uint[](3); Suppose I try to access arr from within an assembly block (using mload, for example). Where (...
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1answer
105 views

Solidity: Convert from “bytes memory” to “address”

I'm using solidity 0.5.0 and when i try to compile my contract it's giving me this error Explicit type conversion not allowed from "bytes memory" to "address" my code is this: /// @dev get broker ...
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1answer
51 views

why a parameter must be “storage” or “memory”?

I am creating a token like this: pragma solidity ^0.5.0; import "../utils/math/SafeMath.sol"; contract ExampleDivisibleNFTs { using SafeMath for uint256; // Percentage of ownership over a ...
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1answer
24 views

How do programs on the 'Ethereum World Computer' compare to traditional programs or websites?

So this question has been bugging for me for a while and I can't seem to find the answer to it. Context I have been a web developer for many years. When I access a website, any frontend code is run ...
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0answers
20 views

Calling private function from external - where are referenced type parameters stored in the end?

Let's assume we have something like: contract C { function externalFunction(uint256[] calldata data) external { privateFunction(data); } function privateFunction(uint256[] memory data)...
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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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2answers
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how does Storing and Fetching data works in Smart contracts [closed]

Please help me out with these questions. 1)Where does the contract stores the data? 2)when we access the value of a variable form of a contract, how does it retrieve the latest value? 3)how is the ...
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1answer
92 views

error: data location must be storage or memory for parameter in funtion but none was given solidity [duplicate]

pragma solidity ^0.5.0; contract Election{ //model a candidates struct candidate { uint id; string name; uint votecount; } //store candidates //fetch candidate mapping(uint =...
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2answers
338 views

How much data can I store in a smart contract, what is the cost and how it is implemented?

If I suppose I use a smart contract as a database, how much data can I store? speaking only of strings and integers, save them in contract data structures does it cost in addition to the gas used for ...
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1answer
27 views

Cannot retrieve data from smartcontract during tests

I am writing truffle tests for my smart contract solidity version 0.4.24. The tests are emitting events to write data to memory through smart contract. But I am unable to retrieve data from functions. ...
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1answer
123 views

Switching from 'storage' to 'memory' increases the gas-cost

I've read several related answers and blog posts, all of them suggesting that for the sake of reading complex state variables (i.e., arrays and structures), one should always prefer declaring the ...
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2answers
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How could Solidity 0.5.0 dynamic sized parameters be declared as storage?

As I understand it 'memory' in the EVM is a byte array and cannot be dynamically resized, whereas 'storage' is able to be resized. What is happening when a parameter is declared as storage. Where is ...
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525 views

FATAL ERROR: Rebalance Allocation failed - process out of memory

So while running truffle compile for my contracts on AWS Ubuntu server I got the following error: <--- Last few GCs ---> [17055:0x3985730] 11958 ms: Scavenge 511.7 (553.4) -> 506.9 (553.4) ...
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0answers
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Why is an address changing when I add it to an array?

I'm encountering a memory / storage issue (I think) w/ an array of addresses where I want to swap out one address with another. Here's how I've initialized the array: address[] public maintainers; ...
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20 views

How to get live mempool transactions whitout full blokchain

I just want to analyse all mempool txs in realtime. I cant use an api because after several requests my ip gets blocked for some minutes, so I dont get the txs in this time. Thank you for help.
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2answers
10k views

TypeError: Data location must be “storage” or “memory” for parameter in function, but none was given

/// @dev Adds a new transaction to the transaction mapping, if transaction does not exist yet. /// @param destination Transaction target address. /// @param value Transaction ether value. /// @param ...
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2answers
89 views

Where are local variables of Primitive (Elementary) data types stored in Solidity

Though in the latest solidity compiler versions, it has been made clear that for reference variables local to a function, one needs to now explicitly mention its location modifier (memory, storage), ...
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1answer
40 views

Finding the memory position of mapping(address => uint) using JavaScript

I am wanting to read data from internal mappings with the following structures: mapping (uint256 => uint256) internal nums; mapping (address => uint256) internal addrToInt; Finding the memory ...
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2answers
139 views

What is the proper pattern to use a temporary variable and ensure it gets stored?

A contract has a state variable, which is complex. For the example, lets say it is a mapping of structs. Inside a method, I want to access that and store the changes. Like so: contract FooManager { ...
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getLogs RPC makes filters?

I am stuggling with memory explosion issue of Parity on my EC2 instance. The memory usage of it keeps increasing gradually. I suspect that getLogs API call makes some garbage on the node. But I ...
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1answer
288 views

memory keyword in function argument

What does the memory keyword in the argument of a function do? pragma solidity 0.4.24; pragma experimental "ABIEncoderV2"; contract Conditional { struct Condition { address to; bytes4 ...
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1answer
301 views

Creating a 2D in-memory array in Solidity

I'm trying to work with 2D in-memory arrays in Solidity, in which the size is not known at compile time. I've noticed that if I define the array size as a constant, then I can use this syntax, which ...
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3answers
247 views

Should I use `storage` or `memory` when just reading the value and not changing state?

pragma solidity 0.4.24; contract Test { struct Book { uint id; } Book[] books; uint public status; constructor() public { books.push(Book(10)); } ...
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1answer
50 views

How can I get the content of storage and memory in my private chain?

I'm looking for some methods to know the content of storage and memory while the contract is running.Mayba some useful tools or abi ? By the way, the abi of geth, debug_writeMemProfile and ...
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1answer
307 views

Declaring a memory array of storage pointers in Solidity

I would like to declare a variable as a memory array of pointers to storage arrays of uint256. For example: pragma solidity ^0.4.24; contract A { uint256[] public array0; uint256[] public ...
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1answer
648 views

Help with setting up Private POA(Clique) Ethereum Network

Geth Version : 1.8.12-stable-37685930 Testing on Amazon EC2 t2.large(8GB RAM) machine with Ubuntu 16.04 running. I am in need of setting up a multi node private POA(Clique) ethereum network. ...
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1answer
118 views

Solidity state variable resets to default inside function

For this project, I am coding smart contracts for Ethereum using Solidity. In the following code, the variable numCertificates should initially be 1. Nonetheless, newCertificateId is 0 when assigned. ...
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2answers
184 views

How to pop from (decrease the length of) a memory array in Solidity

I have a function that gets an address array from another contract, conditionally deletes the msg.sender from the array, then saves the new array back to that contract. Because the array backerList ...
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1answer
258 views

Always use “memory” for variables created within functions. Bad practice?

Is it bad practice to systematically use the memory keyword for variables declared within a function (other than constructor)?
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1answer
140 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: ...
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2answers
5k views

The difference between contract address and wallet address

Disclaimer: this is a rather long question. To my understanding, contract address and wallet address are two profoundly different concepts, with the only thing in common being the fact that they are ...
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1answer
247 views

Why do arrays declared within functions reference storage point 0 by default?

According to the Solidity Documentation, for the following code, ". . . the compiler interprets x as a storage pointer and will make it point to the storage slot 0 by default. This has the effect ...
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1answer
114 views

how to replace an array in a mapping?

I'm learning solidity right now and making a dApp where users get paid to perform actions. Actions are paid based on certain criteria. Since I can't schedule a cron job on ethereum, I can only pay ...
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2answers
1k views

Why cryptokitties uses storage instead of memory?

There are a lot of explainations of storage and memory out there like this question or this question. But I'm wondering why cryptokitties for example uses storage instead of memory in many functions. ...
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0answers
125 views

Solidity memory pointer

Is there any way I can use a local parameter within multiple functions? The idea is to save gas when calling functions. A parameter wouldn't have to be copied and be returned every time. Here's some ...
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1answer
4k views

GPU'S Failed cannot create DAG

Last night everything is fine and then this morning I check my mining its's closed I think it was restarted or close accidentally then when I open my pool I have this error. ETH: 5 pools are ...
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3answers
248 views

value types(uint, bool, etc) as local variable is set to memory initially?

According to this answer, it says simpler variables like bool, uint, et cetera are not variable in length, and are therefore defaulted to memory, whereas this one mentions uint256 v; is default to ...
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0answers
131 views

Quorum failure - Failed to decode message from payload

We use in our project -JP Morgan Quorum (Ethereum based) bloackchain - with istanbul voting mode. We have 4 nodes (3 of them are validators - hard coded, nonchangable) And from time to time (...
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2answers
3k views

How to fill dynamic in-memory array

For some reason solidity doesn't allow to push values into memory array Member "push" is not available in bytes32[] memory outside of storage. Here is sample contract code: pragma solidity ^0.4....
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0answers
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Solidity VM memory management

I'm trying to do an external function call in assembly. So I have to prepare a memory area that store the input args. But where's the address that I should start with mstore? I mean, there are some ...
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1answer
498 views

I got “ TypeError: Storage location can only ..”

Here is my sample contract code, but I got an error, TypeError: Storage location can only be given for array or struct types. I just wannted to define some element of a structure in a function, ...
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1answer
209 views

Can marking object as 'memory' before pushing in Array save gas?

We have a struct: struct structEx { uint num; } And an array: structEx[] arr; Have a look at this code snippet, which just instantiates the struct and push: function f() public { structEx s =...