问题描述
我正在创建基于 BEP20Token 模板 (https://github.com/binance-chain/bsc-genesis-contract/blob/master/contracts/bep20_template/BEP20Token.template) 的智能合约（BEP20 令牌）。 修改了公共构造函数以添加一些令牌详细信息。但是，所有标准函数都存在编译时问题，例如缺少覆盖函数。
**这里是源代码**
// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.2;
interface IBEP20 {
/**
* @dev Returns the amount of tokens in existence.
*/
function totalSupply() external view returns (uint256);
/**
* @dev Returns the token decimals.
*/
function decimals() external view returns (uint8);
/**
* @dev Returns the token symbol.
*/
function symbol() external view returns (string memory);
/**
* @dev Returns the token name.
*/
function name() external view returns (string memory);
/**
* @dev Returns the bep token owner.
*/
function getowner() external view returns (address);
/**
* @dev Returns the amount of tokens owned by `account`.
*/
function balanceOf(address account) external view returns (uint256);
/**
* @dev Moves `amount` tokens from the caller's account to `recipient`.
*
* Returns a boolean value indicating whether the operation succeeded.
*
* Emits a {Transfer} event.
*/
function transfer(address recipient,uint256 amount) external returns (bool);
/**
* @dev Returns the remaining number of tokens that `spender` will be
* allowed to spend on behalf of `owner` through {transferFrom}. This is
* zero by default.
*
* This value changes when {approve} or {transferFrom} are called.
*/
function allowance(address _owner,address spender) external view returns (uint256);
/**
* @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
*
* Returns a boolean value indicating whether the operation succeeded.
*
* IMPORTANT: Beware that changing an allowance with this method brings the risk
* that someone may use both the old and the new allowance by unfortunate
* transaction ordering. One possible solution to mitigate this race
* condition is to first reduce the spender's allowance to 0 and set the
* desired value afterwards:
* https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
*
* Emits an {Approval} event.
*/
function approve(address spender,uint256 amount) external returns (bool);
/**
* @dev Moves `amount` tokens from `sender` to `recipient` using the
* allowance mechanism. `amount` is then deducted from the caller's
* allowance.
*
* Returns a boolean value indicating whether the operation succeeded.
*
* Emits a {Transfer} event.
*/
function transferFrom(address sender,address recipient,uint256 amount) external returns (bool);
/**
* @dev Emitted when `value` tokens are moved from one account (`from`) to
* another (`to`).
*
* Note that `value` may be zero.
*/
event Transfer(address indexed from,address indexed to,uint256 value);
/**
* @dev Emitted when the allowance of a `spender` for an `owner` is set by
* a call to {approve}. `value` is the new allowance.
*/
event Approval(address indexed owner,address indexed spender,uint256 value);
}
/*
* @dev Provides information about the current execution context,including the
* sender of the transaction and its data. While these are generally available
* via msg.sender and msg.data,they should not be accessed in such a direct
* manner,since when dealing with GSN Meta-transactions the account sending and
* paying for execution may not be the actual sender (as far as an application
* is concerned).
*
* This contract is only required for intermediate,library-like contracts.
*/
contract Context {
// Empty internal constructor,to prevent people from mistakenly deploying
// an instance of this contract,which should be used via inheritance.
constructor () internal { }
function _msgSender() internal view returns (address payable) {
return msg.sender;
}
function _msgData() internal view returns (bytes memory) {
this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
return msg.data;
}
}
/**
* @dev Wrappers over solidity's arithmetic operations with added overflow
* checks.
*
* Arithmetic operations in solidity wrap on overflow. This can easily result
* in bugs,because programmers usually assume that an overflow raises an
* error,which is the standard behavior in high level programming languages.
* `SafeMath` restores this intuition by reverting the transaction when an
* operation overflows.
*
* Using this library instead of the unchecked operations eliminates an entire
* class of bugs,so it's recommended to use it always.
*/
library SafeMath {
/**
* @dev Returns the addition of two unsigned integers,reverting on
* overflow.
*
* Counterpart to solidity's `+` operator.
*
* Requirements:
* - Addition cannot overflow.
*/
function add(uint256 a,uint256 b) internal pure returns (uint256) {
uint256 c = a + b;
require(c >= a,"SafeMath: addition overflow");
return c;
}
/**
* @dev Returns the subtraction of two unsigned integers,reverting on
* overflow (when the result is negative).
*
* Counterpart to solidity's `-` operator.
*
* Requirements:
* - Subtraction cannot overflow.
*/
function sub(uint256 a,uint256 b) internal pure returns (uint256) {
return sub(a,b,"SafeMath: subtraction overflow");
}
/**
* @dev Returns the subtraction of two unsigned integers,reverting with custom message on
* overflow (when the result is negative).
*
* Counterpart to solidity's `-` operator.
*
* Requirements:
* - Subtraction cannot overflow.
*/
function sub(uint256 a,uint256 b,string memory errorMessage) internal pure returns (uint256) {
require(b <= a,errorMessage);
uint256 c = a - b;
return c;
}
/**
* @dev Returns the multiplication of two unsigned integers,reverting on
* overflow.
*
* Counterpart to solidity's `*` operator.
*
* Requirements:
* - Multiplication cannot overflow.
*/
function mul(uint256 a,uint256 b) internal pure returns (uint256) {
// Gas optimization: this is cheaper than requiring 'a' not being zero,but the
// benefit is lost if 'b' is also tested.
// See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
if (a == 0) {
return 0;
}
uint256 c = a * b;
require(c / a == b,"SafeMath: multiplication overflow");
return c;
}
/**
* @dev Returns the integer division of two unsigned integers. Reverts on
* division by zero. The result is rounded towards zero.
*
* Counterpart to solidity's `/` operator. Note: this function uses a
* `revert` opcode (which leaves remaining gas untouched) while solidity
* uses an invalid opcode to revert (consuming all remaining gas).
*
* Requirements:
* - The divisor cannot be zero.
*/
function div(uint256 a,uint256 b) internal pure returns (uint256) {
return div(a,"SafeMath: division by zero");
}
/**
* @dev Returns the integer division of two unsigned integers. Reverts with custom message on
* division by zero. The result is rounded towards zero.
*
* Counterpart to solidity's `/` operator. Note: this function uses a
* `revert` opcode (which leaves remaining gas untouched) while solidity
* uses an invalid opcode to revert (consuming all remaining gas).
*
* Requirements:
* - The divisor cannot be zero.
*/
function div(uint256 a,string memory errorMessage) internal pure returns (uint256) {
// solidity only automatically asserts when dividing by 0
require(b > 0,errorMessage);
uint256 c = a / b;
// assert(a == b * c + a % b); // There is no case in which this doesn't hold
return c;
}
/**
* @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),* Reverts when dividing by zero.
*
* Counterpart to solidity's `%` operator. This function uses a `revert`
* opcode (which leaves remaining gas untouched) while solidity uses an
* invalid opcode to revert (consuming all remaining gas).
*
* Requirements:
* - The divisor cannot be zero.
*/
function mod(uint256 a,uint256 b) internal pure returns (uint256) {
return mod(a,"SafeMath: modulo by zero");
}
/**
* @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),* Reverts with custom message when dividing by zero.
*
* Counterpart to solidity's `%` operator. This function uses a `revert`
* opcode (which leaves remaining gas untouched) while solidity uses an
* invalid opcode to revert (consuming all remaining gas).
*
* Requirements:
* - The divisor cannot be zero.
*/
function mod(uint256 a,string memory errorMessage) internal pure returns (uint256) {
require(b != 0,errorMessage);
return a % b;
}
}
/**
* @dev Contract module which provides a basic access control mechanism,where
* there is an account (an owner) that can be granted exclusive access to
* specific functions.
*
* By default,the owner account will be the one that deploys the contract. This
* can later be changed with {transferOwnership}.
*
* This module is used through inheritance. It will make available the modifier
* `onlyOwner`,which can be applied to your functions to restrict their use to
* the owner.
*/
contract Ownable is Context {
address private _owner;
event OwnershipTransferred(address indexed prevIoUsOwner,address indexed newOwner);
/**
* @dev Initializes the contract setting the deployer as the initial owner.
*/
constructor () internal {
address msgSender = _msgSender();
_owner = msgSender;
emit OwnershipTransferred(address(0),msgSender);
}
/**
* @dev Returns the address of the current owner.
*/
function owner() public view returns (address) {
return _owner;
}
/**
* @dev Throws if called by any account other than the owner.
*/
modifier onlyOwner() {
require(_owner == _msgSender(),"Ownable: caller is not the owner");
_;
}
/**
* @dev Leaves the contract without owner. It will not be possible to call
* `onlyOwner` functions anymore. Can only be called by the current owner.
*
* NOTE: Renouncing ownership will leave the contract without an owner,* thereby removing any functionality that is only available to the owner.
*/
function renounceOwnership() public onlyOwner {
emit OwnershipTransferred(_owner,address(0));
_owner = address(0);
}
/**
* @dev Transfers ownership of the contract to a new account (`newOwner`).
* Can only be called by the current owner.
*/
function transferOwnership(address newOwner) public onlyOwner {
_transferOwnership(newOwner);
}
/**
* @dev Transfers ownership of the contract to a new account (`newOwner`).
*/
function _transferOwnership(address newOwner) internal {
require(newOwner != address(0),"Ownable: new owner is the zero address");
emit OwnershipTransferred(_owner,newOwner);
_owner = newOwner;
}
}
contract BEP20Token is Context,IBEP20,Ownable {
using SafeMath for uint256;
mapping (address => uint256) private _balances;
mapping (address => mapping (address => uint256)) private _allowances;
uint256 private _totalSupply;
uint8 private _decimals;
string private _symbol;
string private _name;
constructor() public {
_name = "Money Paiger Coin";
_symbol = "MPTT";
_decimals = 18;
_totalSupply = 10000000 * 10 ** 18; //10 million Total Supply
_balances[msg.sender] = _totalSupply;
emit Transfer(address(0),msg.sender,_totalSupply);
}
/**
* @dev Returns the bep token owner.
*/
function getowner() external view returns (address) {
return owner();
}
/**
* @dev Returns the token decimals.
*/
function decimals() external view returns (uint8) {
return _decimals;
}
/**
* @dev Returns the token symbol.
*/
function symbol() external view returns (string memory) {
return _symbol;
}
/**
* @dev Returns the token name.
*/
function name() external view returns (string memory) {
return _name;
}
/**
* @dev See {BEP20-totalSupply}.
*/
function totalSupply() external view returns (uint256) {
return _totalSupply;
}
/**
* @dev See {BEP20-balanceOf}.
*/
function balanceOf(address account) external view returns (uint256) {
return _balances[account];
}
/**
* @dev See {BEP20-transfer}.
*
* Requirements:
*
* - `recipient` cannot be the zero address.
* - the caller must have a balance of at least `amount`.
*/
function transfer(address recipient,uint256 amount) external returns (bool) {
_transfer(_msgSender(),recipient,amount);
return true;
}
/**
* @dev See {BEP20-allowance}.
*/
function allowance(address owner,address spender) external view returns (uint256) {
return _allowances[owner][spender];
}
/**
* @dev See {BEP20-approve}.
*
* Requirements:
*
* - `spender` cannot be the zero address.
*/
function approve(address spender,uint256 amount) external returns (bool) {
_approve(_msgSender(),spender,amount);
return true;
}
/**
* @dev See {BEP20-transferFrom}.
*
* Emits an {Approval} event indicating the updated allowance. This is not
* required by the EIP. See the note at the beginning of {BEP20};
*
* Requirements:
* - `sender` and `recipient` cannot be the zero address.
* - `sender` must have a balance of at least `amount`.
* - the caller must have allowance for `sender`'s tokens of at least
* `amount`.
*/
function transferFrom(address sender,uint256 amount) external returns (bool) {
_transfer(sender,amount);
_approve(sender,_msgSender(),_allowances[sender][_msgSender()].sub(amount,"BEP20: transfer amount exceeds allowance"));
return true;
}
/**
* @dev Atomically increases the allowance granted to `spender` by the caller.
*
* This is an alternative to {approve} that can be used as a mitigation for
* problems described in {BEP20-approve}.
*
* Emits an {Approval} event indicating the updated allowance.
*
* Requirements:
*
* - `spender` cannot be the zero address.
*/
function increaseAllowance(address spender,uint256 addedValue) public returns (bool) {
_approve(_msgSender(),_allowances[_msgSender()][spender].add(addedValue));
return true;
}
/**
* @dev Atomically decreases the allowance granted to `spender` by the caller.
*
* This is an alternative to {approve} that can be used as a mitigation for
* problems described in {BEP20-approve}.
*
* Emits an {Approval} event indicating the updated allowance.
*
* Requirements:
*
* - `spender` cannot be the zero address.
* - `spender` must have allowance for the caller of at least
* `subtractedValue`.
*/
function decreaseAllowance(address spender,uint256 subtractedValue) public returns (bool) {
_approve(_msgSender(),_allowances[_msgSender()][spender].sub(subtractedValue,"BEP20: decreased allowance below zero"));
return true;
}
/**
* @dev Creates `amount` tokens and assigns them to `msg.sender`,increasing
* the total supply.
*
* Requirements
*
* - `msg.sender` must be the token owner
*/
function mint(uint256 amount) public onlyOwner returns (bool) {
_mint(_msgSender(),amount);
return true;
}
/**
* @dev Moves tokens `amount` from `sender` to `recipient`.
*
* This is internal function is equivalent to {transfer},and can be used to
* e.g. implement automatic token fees,slashing mechanisms,etc.
*
* Emits a {Transfer} event.
*
* Requirements:
*
* - `sender` cannot be the zero address.
* - `recipient` cannot be the zero address.
* - `sender` must have a balance of at least `amount`.
*/
function _transfer(address sender,uint256 amount) internal {
require(sender != address(0),"BEP20: transfer from the zero address");
require(recipient != address(0),"BEP20: transfer to the zero address");
_balances[sender] = _balances[sender].sub(amount,"BEP20: transfer amount exceeds balance");
_balances[recipient] = _balances[recipient].add(amount);
emit Transfer(sender,amount);
}
/** @dev Creates `amount` tokens and assigns them to `account`,increasing
* the total supply.
*
* Emits a {Transfer} event with `from` set to the zero address.
*
* Requirements
*
* - `to` cannot be the zero address.
*/
function _mint(address account,uint256 amount) internal {
require(account != address(0),"BEP20: mint to the zero address");
_totalSupply = _totalSupply.add(amount);
_balances[account] = _balances[account].add(amount);
emit Transfer(address(0),account,amount);
}
/**
* @dev Destroys `amount` tokens from `account`,reducing the
* total supply.
*
* Emits a {Transfer} event with `to` set to the zero address.
*
* Requirements
*
* - `account` cannot be the zero address.
* - `account` must have at least `amount` tokens.
*/
function _burn(address account,"BEP20: burn from the zero address");
_balances[account] = _balances[account].sub(amount,"BEP20: burn amount exceeds balance");
_totalSupply = _totalSupply.sub(amount);
emit Transfer(account,address(0),amount);
}
/**
* @dev Sets `amount` as the allowance of `spender` over the `owner`s tokens.
*
* This is internal function is equivalent to `approve`,and can be used to
* e.g. set automatic allowances for certain subsystems,etc.
*
* Emits an {Approval} event.
*
* Requirements:
*
* - `owner` cannot be the zero address.
* - `spender` cannot be the zero address.
*/
function _approve(address owner,address spender,uint256 amount) internal {
require(owner != address(0),"BEP20: approve from the zero address");
require(spender != address(0),"BEP20: approve to the zero address");
_allowances[owner][spender] = amount;
emit Approval(owner,amount);
}
/**
* @dev Destroys `amount` tokens from `account`.`amount` is then deducted
* from the caller's allowance.
*
* See {_burn} and {_approve}.
*/
function _burnFrom(address account,uint256 amount) internal {
_burn(account,amount);
_approve(account,_allowances[account][_msgSender()].sub(amount,"BEP20: burn amount exceeds allowance"));
}
}
几个问题
-
Constructor public () - 警告：忽略构造函数的可见性。如果您希望合约不可部署，则使其“抽象”就足够了。
-
function getowner() - 类型错误：覆盖函数缺少“覆盖”说明符。 --> MoneyPaigerToken.sol:365:3: | 365 |函数 getowner
不确定这里缺少什么。
问候 山姆
解决方法
Constructor public () - 警告：忽略构造函数的可见性。如果您希望合约不可部署，则使其“抽象”就足够了。
警告信息说明了一切。您可以安全地删除 public 可见性修饰符，因为它无论如何都会被忽略。
如果您标记了 BEP20Token 合同摘要，您将需要从它继承一个子合同，不能部署 BEP20Token 本身，但必须部署子合同。在这种情况下，这不是您想要的。
constructor() { // remove the `public` modifier
function getOwner() - 类型错误：覆盖函数缺少“覆盖”说明符。 --> MoneyPaigerToken.sol:365:3: | 365 |函数 getOwner
在 Solidity 中使用接口与在大多数其他语言中不同。使用其他语言的表达式，implements（接口）没有关键字。只有 extends（父类） - 在 Solidity 中简单地称为 is（类的子类）。
当您与其他合约（部署在不同地址上）交互时，通常会使用接口。示例：
function getOtherTokenDecimals(address tokenAddress) external returns (uint8) {
IBEP20 tokenInstance = IBEP20(tokenAddress);
return tokenInstance.decimals();
}
正如我之前写的，目前没有实现接口的契约的表达式。只是为了扩展一个类。因此，您的 BEP20Token is IBEP20 扩展了（接口）类，并且因为函数 getOwner() 已在父类中定义，您需要使用 override 修饰符明确声明您要覆盖。
function getOwner() external override view returns (address) { // add the `override` modifier
但是，我的方法不是显式覆盖函数，而是将事件定义移动到您的 BEP20Token，删除接口定义及其继承，因为它没有在代码中的任何其他地方使用。
contract BEP20Token is Context,Ownable { // remove the `IBEP20` inheritance
// move the event definitions here
event Transfer(address indexed from,address indexed to,uint256 value);
event Approval(address indexed owner,address indexed spender,uint256 value);
您还可以从 Context 父项列表中删除 BEP20Token，因为 Ownable 也继承自 Context。
contract BEP20Token is Ownable { // remove the `Context` parent
如错误中所述，您必须使用 'override' 修饰符显式覆盖子合约中的函数。
function getOwner() override external view returns (address);然后通过添加 'virtual' 修饰符使您想要在父合约中覆盖的函数成为虚拟的。