如何在此 ERC20 合约中设置总供应量？

如何解决如何在此 ERC20 合约中设置总供应量？

我从 openzeppelin 复制并粘贴了示例 ERC20 合约，但由于某种原因，我无法找到可以设置 TotalSupply 的位置。

pragma solidity >=0.6.0 <0.8.0;

import "../../GSN/Context.sol";
import "./IERC20.sol";
import "../../math/SafeMath.sol";

contract ERC20 is Context,IERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

    constructor (string memory name_,string memory symbol_) public {
        _name = name_;
        _symbol = symbol_;
        _decimals = 18;
    }

    function name() public view returns (string memory) {
        return _name;
    }

    function symbol() public view returns (string memory) {
        return _symbol;
    }

    function decimals() public view returns (uint8) {
        return _decimals;
    }

    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    function transfer(address recipient,uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(),recipient,amount);
        return true;
    }

    function allowance(address owner,address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    function approve(address spender,uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(),spender,amount);
        return true;
    }

    function transferFrom(address sender,address recipient,uint256 amount) public virtual override returns (bool) {
        _transfer(sender,amount);
        _approve(sender,_msgSender(),_allowances[sender][_msgSender()].sub(amount,"ERC20: transfer amount exceeds allowance"));
        return true;
    }

    function increaseAllowance(address spender,uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(),_allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

    function decreaseAllowance(address spender,uint256 subtractedValue) public virtual returns (bool) {
        _approve(_msgSender(),_allowances[_msgSender()][spender].sub(subtractedValue,"ERC20: decreased allowance below zero"));
        return true;
    }

    function _transfer(address sender,uint256 amount) internal virtual {
        require(sender != address(0),"ERC20: transfer from the zero address");
        require(recipient != address(0),"ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender,amount);

        _balances[sender] = _balances[sender].sub(amount,"ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender,amount);
    }

    function _mint(address account,uint256 amount) internal virtual {
        require(account != address(0),"ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0),account,amount);

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0),amount);
    }

    function _burn(address account,"ERC20: burn from the zero address");

        _beforeTokenTransfer(account,address(0),amount);

        _balances[account] = _balances[account].sub(amount,"ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account,amount);
    }

    function _approve(address owner,address spender,uint256 amount) internal virtual {
        require(owner != address(0),"ERC20: approve from the zero address");
        require(spender != address(0),"ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner,amount);
    }

  
    function _setupDecimals(uint8 decimals_) internal {
        _decimals = decimals_;
    }

    function _beforeTokenTransfer(address from,address to,uint256 amount) internal virtual { }
}

我可以设置 TokenName 和 Symbol 以及 Decimals 但我不能设置总供应量

我也遇到无法导入“math/SafeMath.sol”的问题：找不到文件 我不明白他们为什么发布甚至不起作用的代码？ 有人可以帮我解决这个问题

解决方法

关于SafeMath：

Openzeppelin 在他们的项目中实现了 SafeMath，所以如果你只是复制了 ERC20，你就错过了 SafeMath 的实现。如果你克隆整个项目，这个问题就解决了。

关于totalSupply：

这个实现是一个 ERC20 可铸代币。如果您检查函数 _mint，您会看到每次调用此函数时 _totalSupply 都会增加。您从 0 开始，那么如果您铸造 10，您的总供应量将是 10，依此类推。

如果您想设置您的总供应量，您可以更改构造函数以允许您设置 _totalSupply：

constructor (string memory name_,string memory symbol_,uint256 totalSupply_) public {
        _name = name_;
        _symbol = symbol_;
        _decimals = 18;
        _totalSupply = totalSupply_;
        _balances[msg.sender] = totalSupply_;
        emit Transfer(address(0),msg.sender,totalSupply_); // Optional
    }

您还可以通过删除 _mint 函数来防止铸造以增加总供应量。