The Error: Source “@openzeppelin/contracts/token/ERC20/ERC20.sol” not found: File import callback not supported Step 1: Install the Solidity Extention Step 2: Right click on the error. Select “Change the default workspace…” Step 3: Select localNodeModule Might have to restart the IDE
Please use this to send your transaction: transaction = SimpleStorage.constructor().buildTransaction( { “gasPrice”: w3.eth.gas_price, “chainId”: chain_id, “from”: my_address, “nonce”: nonce, }
Yes you can, by using some EVM assembly code to get the address’ code size: function isContract(address addr) returns (bool) { uint size; assembly { size := extcodesize(addr) } return size > 0; }
In solidity every variable is set to 0 by default. You should think of mappings as all possible combinations are set to 0 by default. In your specific case I would use the following: if (buyers[msg.sender].amount == 0)
solidity ^0.8.0 import “@openzeppelin/contracts/utils/Strings.sol”; Strings.toString(myUINT) works for me. https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/Strings.sol#L15-L35
From Solidity ^0.6.8 SPDX license is introduced. So you need to use SPDX-License-Identifier in the code. Have a look at this: https://forum.openzeppelin.com/t/solidity-0-6-8-introduces-spdx-license-identifiers/2859 For example in your code you need to use license identifier like // SPDX-License-Identifier: MIT pragma solidity ^0.7.5; contract TestContract { // Some logic } You need to use license according to your … Read more
You should add memory keyword for string parameter, which was introduced in solidity version 0.5.0 As per the documentation: Explicit data location for all variables of struct, array or mapping types is now mandatory. This is also applied to function parameters and return variables. For example, change uint[] x = m_x to uint[] storage x … Read more
Within an Ethereum transaction, the zero-account is just a special case used to indicate that a new contract is being deployed. It is literally ‘0x0’ set to the to field in the raw transaction. Every Ethereum transaction, whether it’s a transfer between two external accounts, a request to execute contract code, or a request to … Read more
Without the memory keyword, Solidity tries to declare variables in storage. Lead Solidity dev chriseth: “You can think of storage as a large array that has a virtual structure… a structure you cannot change at runtime – it is determined by the state variables in your contract”. That is, the structure of storage is set … Read more