ethereum - Solidity overriding function is missing "override" specifier

Question

I'm using some templated code to create a token. Unfortunately I am running into the following error.

Screenshot attached, with code below. Using remix.ethereum. Identical error on each function. What's causing this and how do I fix it?

EDIT - I've added code showing the interface, constructor, etc. This is all the code now.

pragma solidity >=0.7.0 <0.9.0;

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address tokenOwner) external view returns (uint256 balance);
    function allowance(address tokenOwner, address spender) external view returns (uint256 remaining);
    function transfer(address to, uint tokens) external returns (bool success);
    function approve(address spender, uint tokens) external returns (bool success);
    function transferFrom(address from, address to, uint256 tokens) external returns (bool success);

    event Transfer(address indexed from, address indexed to, uint256 tokens);
    event Approval(address indexed tokenOwner, address indexed spender, uint256 tokens);
}

// ----------------------------------------------------------------------------
// Safe Math Library
// ----------------------------------------------------------------------------
contract SafeMath {
    function safeAdd(uint a, uint b) public pure returns (uint c) {
        c = a + b;
        require(c >= a);
    }
    function safeSub(uint a, uint b) public pure returns (uint c) {
        require(b <= a); c = a - b; 
        
    } 
    function safeMul(uint a, uint b) public pure returns (uint c) { 
        c = a * b; require(a == 0 || c / a == b); 
        
    } 
    function safeDiv(uint a, uint b) public pure returns (uint c) { 
        require(b > 0);
        c = a / b;
    }
}


contract TTKN is IERC20, SafeMath {
    string public name;
    string public symbol;
    uint8 public decimals; // 18 decimals is the strongly suggested default, avoid changing it

    uint256 public _totalSupply;

    mapping(address => uint256) balances;
    mapping(address => mapping(address => uint256)) allowed;

    /**
     * Constrctor function
     *
     * Initializes contract with initial supply tokens to the creator of the contract
     */
    constructor() {
        name = "Test Token";
        symbol = "TTKN";
        decimals = 18;
        _totalSupply = 100000000000000000000000000;

        balances[msg.sender] = _totalSupply;
        emit Transfer(address(0), msg.sender, _totalSupply);
    }

function totalSupply() public view returns (uint256) {
    return _totalSupply  - balances[address(0)];
}

function balanceOf(address tokenOwner) public view returns (uint256 balance) {
    return balances[tokenOwner];
}

function allowance(address tokenOwner, address spender) public view returns (uint256 remaining) {
    return allowed[tokenOwner][spender];
}

function approve(address spender, uint256 tokens) public returns (bool success) {
    allowed[msg.sender][spender] = tokens;
    emit Approval(msg.sender, spender, tokens);
    return true;
}

function transfer(address to, uint256 tokens) public returns (bool success) {
    balances[msg.sender] = safeSub(balances[msg.sender], tokens);
    balances[to] = safeAdd(balances[to], tokens);
    emit Transfer(msg.sender, to, tokens);
    return true;
}

function transferFrom(address from, address to, uint256 tokens) public returns (bool success) {
    balances[from] = safeSub(balances[from], tokens);
    allowed[from][msg.sender] = safeSub(allowed[from][msg.sender], tokens);
    balances[to] = safeAdd(balances[to], tokens);
    emit Transfer(from, to, tokens);
    return true;
}

标签： ethereumsolidity

Answer 1

您要做的是实施 ERC20 代币。你的代码必须符合标准，这是怎么做到的？带有接口（您的代码）。这个接口的作用是强制你的代码包含某些方法来满足标准。（您可以在不使用接口的情况下创建您的令牌，但要实现所有 EIP-20 标准）

EIP-20：代币标准

Solidity 是一种支持多重继承的面向对象的编程语言。您可以从基础合约继承，然后覆盖该基础合约中的函数。在 Solidity 0.6 之前，无法知道应该重写哪些函数。现在，您可以将函数显式标记为虚拟或覆盖。

官方文档——覆盖

// SPDX-License-Identifier: Unlicensed

pragma solidity >=0.7.0 <0.9.0;

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address tokenOwner) external view returns (uint256 balance);
    function allowance(address tokenOwner, address spender) external view returns (uint256 remaining);
    function transfer(address to, uint tokens) external returns (bool success);
    function approve(address spender, uint tokens) external returns (bool success);
    function transferFrom(address from, address to, uint256 tokens) external returns (bool success);

    event Transfer(address indexed from, address indexed to, uint256 tokens);
    event Approval(address indexed tokenOwner, address indexed spender, uint256 tokens);
}

// ----------------------------------------------------------------------------
// Safe Math Library
// ----------------------------------------------------------------------------
contract SafeMath {
    function safeAdd(uint a, uint b) public pure returns (uint c) {
        c = a + b;
        require(c >= a);
    }
    function safeSub(uint a, uint b) public pure returns (uint c) {
        require(b <= a); c = a - b; 
        
    } 
    function safeMul(uint a, uint b) public pure returns (uint c) { 
        c = a * b; require(a == 0 || c / a == b); 
        
    } 
    function safeDiv(uint a, uint b) public pure returns (uint c) { 
        require(b > 0);
        c = a / b;
    }
}


contract TTKN is IERC20, SafeMath {
    string public name;
    string public symbol;
    uint8 public decimals; // 18 decimals is the strongly suggested default, avoid changing it

    uint256 public _totalSupply;

    mapping(address => uint256) balances;
    mapping(address => mapping(address => uint256)) allowed;

    /**
     * Constrctor function
     *
     * Initializes contract with initial supply tokens to the creator of the contract
     */
    constructor() {
        name = "Test Token";
        symbol = "TTKN";
        decimals = 18;
        _totalSupply = 100000000000000000000000000;

        balances[msg.sender] = _totalSupply;
        emit Transfer(address(0), msg.sender, _totalSupply);
    }

        function totalSupply() public override view returns (uint256) {
            return _totalSupply  - balances[address(0)];
        }

        function balanceOf(address tokenOwner) public override view returns (uint256 balance) {
            return balances[tokenOwner];
        }

        function allowance(address tokenOwner, address spender) public override view returns (uint256 remaining) {
            return allowed[tokenOwner][spender];
        }

        function approve(address spender, uint256 tokens) public override returns (bool success) {
            allowed[msg.sender][spender] = tokens;
            emit Approval(msg.sender, spender, tokens);
            return true;
        }

        function transfer(address to, uint256 tokens) public override returns (bool success) {
            balances[msg.sender] = safeSub(balances[msg.sender], tokens);
            balances[to] = safeAdd(balances[to], tokens);
            emit Transfer(msg.sender, to, tokens);
            return true;
        }

        function transferFrom(address from, address to, uint256 tokens) public override returns (bool success) {
            balances[from] = safeSub(balances[from], tokens);
            allowed[from][msg.sender] = safeSub(allowed[from][msg.sender], tokens);
            balances[to] = safeAdd(balances[to], tokens);
            emit Transfer(from, to, tokens);
            return true;
        }
    }