# ERC20 协议的一个简单实现

By [Untitled](https://paragraph.com/@0xe2c356463af50da872b1639fe827f406a27656ba) · 2021-11-23

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    pragma solidity ^0.4.23;
    
    interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) external; }
    
    contract TokenERC20 {
        
        string public name = "Litex Test Token"; // Set the name for display purposes
        string public symbol = "LTT";  // Set the symbol for display purposes
        
        uint8 public decimals = 18;
        // 18 decimals is the strongly suggested default, avoid changing it
        
        uint256 public totalSupply;
        
        uint256 initialSupply = 100000000000;
    
        // This creates an array with all balances
        mapping (address => uint256) public balanceOf;
        mapping (address => mapping (address => uint256)) public allowance;
    
        // This generates a public event on the blockchain that will notify clients
        event Transfer(address indexed from, address indexed to, uint256 value);
    
        // This notifies clients about the amount burnt
        event Burn(address indexed from, uint256 value);
    
        /
         * Constructor function
         
         * Initializes contract with initial supply tokens to the creator of the contract
         */
        function TokenERC20() public {
            totalSupply = initialSupply * 10 * uint256(decimals); // Update total supply with the decimal amount
            balanceOf[msg.sender] = totalSupply; // Give the creator all initial tokens
        }
    
        /
         * Internal transfer, only can be called by this contract
         /
        function _transfer(address _from, address _to, uint _value) internal {
            // Prevent transfer to 0x0 address. Use burn() instead
            require(_to != 0x0);
            // Check if the sender has enough
            require(balanceOf[_from] >= _value);
            // Check for overflows
            require(balanceOf[_to] + _value >= balanceOf[_to]);
            // Save this for an assertion in the future
            uint previousBalances = balanceOf[_from] + balanceOf[_to];
            // Subtract from the sender
            balanceOf[_from] -= _value;
            // Add the same to the recipient
            balanceOf[_to] += _value;
            emit Transfer(_from, _to, _value);
            // Asserts are used to use static analysis to find bugs in your code. They should never fail
            assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
        }
    
        /
         * Transfer tokens
         *
         * Send _value tokens to _to from your account
         *
         * @param _to The address of the recipient
         * @param _value the amount to send
         */
        function transfer(address _to, uint256 _value) public {
            _transfer(msg.sender, _to, _value);
        }
    
        /
         * Transfer tokens from other address
         *
         * Send _value tokens to _to on behalf of _from
         *
         * @param _from The address of the sender
         * @param _to The address of the recipient
         * @param _value the amount to send
         */
        function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
            require(_value <= allowance[_from][msg.sender]);     // Check allowance
            allowance[_from][msg.sender] -= _value;
            _transfer(_from, _to, _value);
            return true;
        }
    
        /
         * Set allowance for other address
         *
         * Allows _spender to spend no more than _value tokens on your behalf
         *
         * @param _spender The address authorized to spend
         * @param _value the max amount they can spend
         */
        function approve(address _spender, uint256 _value) public
            returns (bool success) {
            allowance[msg.sender][_spender] = _value;
            return true;
        }
    
        /
         * Set allowance for other address and notify
         *
         * Allows _spender to spend no more than _value tokens on your behalf, and then ping the contract about it
         *
         * @param _spender The address authorized to spend
         * @param _value the max amount they can spend
         * @param _extraData some extra information to send to the approved contract
         */
        function approveAndCall(address _spender, uint256 _value, bytes _extraData)
            public
            returns (bool success) {
            tokenRecipient spender = tokenRecipient(_spender);
            if (approve(_spender, _value)) {
                spender.receiveApproval(msg.sender, _value, this, _extraData);
                return true;
            }
        }
    
        /
         * Destroy tokens
         *
         * Remove _value tokens from the system irreversibly
         *
         * @param _value the amount of money to burn
         */
        function burn(uint256 _value) public returns (bool success) {
            require(balanceOf[msg.sender] >= _value);   // Check if the sender has enough
            balanceOf[msg.sender] -= _value;            // Subtract from the sender
            totalSupply -= _value;                      // Updates totalSupply
            emit Burn(msg.sender, _value);
            return true;
        }
    
        /*
         * Destroy tokens from other account
         *
         * Remove _value tokens from the system irreversibly on behalf of _from.
         *
         * @param _from the address of the sender
         * @param _value the amount of money to burn
         */
        function burnFrom(address _from, uint256 _value) public returns (bool success) {
            require(balanceOf[_from] >= _value);                // Check if the targeted balance is enough
            require(_value <= allowance[_from][msg.sender]);    // Check allowance
            balanceOf[_from] -= _value;                         // Subtract from the targeted balance
            allowance[_from][msg.sender] -= _value;             // Subtract from the sender's allowance
            totalSupply -= _value;                              // Update totalSupply
            emit Burn(_from, _value);
            return true;
        }
    }

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*Originally published on [Untitled](https://paragraph.com/@0xe2c356463af50da872b1639fe827f406a27656ba/erc20-2)*