币安BSC智能链发币教程——可自行燃烧通缩或者授权后代燃烧的ERC20代币燃烧合约代码实现【pdf+视频BSC发币教程下载】

通常在合约中用户可以自行燃烧自己钱包地址里的代币，这是比较常见的功能。但是，在部分功能的合约中需要存在可以燃烧授权后的钱包地址的代币余额，只要可以获取指定钱包的代币授权额度，就可以燃烧该额度内的代币到黑洞地址。该功能类似了ERC20标准合约中的transferFrom代转账方法的功能。

允许自行燃烧及获取指定钱包地址的授权额度后代燃烧的合约代码如下：

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.5.0) (token/ERC20/extensions/ERC20Burnable.sol)

pragma solidity ^0.8.0;

import "../ERC20.sol";
import "../../../utils/Context.sol";

/**
 * @dev Extension of {ERC20} that allows token holders to destroy both their own
 * tokens and those that they have an allowance for, in a way that can be
 * recognized off-chain (via event analysis).
 */
abstract contract ERC20Burnable is Context, ERC20 {
    /**
     * @dev Destroys `amount` tokens from the caller.
     *
     * See {ERC20-_burn}.
     */
    function burn(uint256 amount) public virtual {
        _burn(_msgSender(), amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, deducting from the caller's
     * allowance.
     *
     * See {ERC20-_burn} and {ERC20-allowance}.
     *
     * Requirements:
     *
     * - the caller must have allowance for ``accounts``'s tokens of at least
     * `amount`.
     */
    function burnFrom(address account, uint256 amount) public virtual {
        _spendAllowance(account, _msgSender(), amount);
        _burn(account, amount);
    }
}

业务合约通过继承ERC20Burnable合约，获取burn和burnFrom功能。其中burnFrom即为获取指定钱包地址授权代币额度后的代燃烧功能，在实现该功能时需要先校验授权额度并修改燃烧后的授权，_spendAllowance函数的具体代码如下：

/**
     * @dev Updates `owner` s allowance for `spender` based on spent `amount`.
     *
     * Does not update the allowance amount in case of infinite allowance.
     * Revert if not enough allowance is available.
     *
     * Might emit an {Approval} event.
     */
    function _spendAllowance(
        address owner,
        address spender,
        uint256 amount
    ) internal virtual {
        uint256 currentAllowance = allowance(owner, spender);
        if (currentAllowance != type(uint256).max) {
            require(currentAllowance >= amount, "ERC20: insufficient allowance");
            unchecked {
                _approve(owner, spender, currentAllowance - amount);
            }
        }
    }

至此，完成可自行燃烧通缩或者授权后代燃烧的ERC20代币燃烧合约代码实现的所有操作流程。

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