ERC20 代币合约

pragma solidity ^ 0.4 .16; interface tokenRecipient {  function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) external; } contract TokenERC20 { // Public variables of the token string public name; string public symbol; uint8 public decimals = 18; // 18 decimals is the strongly suggested default, avoid changing it  uint256 public totalSupply; // 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 generates a public event on the blockchain that will notify clients  event Approval(address indexed _owner, address indexed _spender, 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(   uint256 initialSupply, string tokenName, string tokenSymbol  ) public {   totalSupply = initialSupply * 10 ** uint256(decimals); /*Update total supply with the   decimal amount*/   balanceOf[msg.sender] = totalSupply; // Give the creator all initial tokens   name = tokenName; // Set the name for display purposes   symbol = tokenSymbol; // Set the symbol for display purposes } /**   * 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 returns(bool success) { _transfer(msg.sender, _to, _value); return true; } /**   * 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;   emit Approval(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; } }