快速学习-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;
	}
}