【以太坊开发】发币指南--进阶篇

参考：https://www.ethereum.org/token

pragma solidity ^0.4.16;interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) external; }contract TokenERC20 {// Public variables of the tokenstring public name;string public symbol;uint8 public decimals = 18;// 18 decimals is the strongly suggested default, avoid changing ituint256 public totalSupply;// This creates an array with all balancesmapping (address => uint256) public balanceOf;mapping (address => mapping (address => uint256)) public allowance;// This generates a public event on the blockchain that will notify clientsevent Transfer(address indexed from, address indexed to, uint256 value);// This generates a public event on the blockchain that will notify clientsevent Approval(address indexed _owner, address indexed _spender, uint256 _value);// This notifies clients about the amount burntevent 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 amountbalanceOf[msg.sender] = totalSupply;                // Give the creator all initial tokensname = tokenName;                                   // Set the name for display purposessymbol = 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() insteadrequire(_to != 0x0);// Check if the sender has enoughrequire(balanceOf[_from] >= _value);// Check for overflowsrequire(balanceOf[_to] + _value >= balanceOf[_to]);// Save this for an assertion in the futureuint previousBalances = balanceOf[_from] + balanceOf[_to];// Subtract from the senderbalanceOf[_from] -= _value;// Add the same to the recipientbalanceOf[_to] += _value;emit Transfer(_from, _to, _value);// Asserts are used to use static analysis to find bugs in your code. They should never failassert(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 allowanceallowance[_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) publicreturns (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)publicreturns (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 enoughbalanceOf[msg.sender] -= _value;            // Subtract from the sendertotalSupply -= _value;                      // Updates totalSupplyemit 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 enoughrequire(_value <= allowance[_from][msg.sender]);    // Check allowancebalanceOf[_from] -= _value;                         // Subtract from the targeted balanceallowance[_from][msg.sender] -= _value;             // Subtract from the sender's allowancetotalSupply -= _value;                              // Update totalSupplyemit Burn(_from, _value);return true;}
}

`approve` 和`allowance`的用法

账户A有1000个ETH，想允许B账户随意调用100个ETH。A账户按照以下形式调用approve函数approve(B,100)。当B账户想用这100个ETH中的10个ETH给C账户时，则调用transferFrom(A, C, 10)。这时调用allowance(A, B)可以查看B账户还能够调用A账户多少个token。

—未完待续—

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【以太坊开发】发币指南--进阶篇

`approve` 和`allowance`的用法

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