totalSupply = initialSupply * 10 ** uint256(decimals);
如果initialSupply = 21000000.000000000000000000（2100万）为什么乘以10？
pragma solidity ^0.4.16;
contract owned {
address public owner;
function owned() public {
owner = msg.sender;
}
modifier onlyOwner {
require(msg.sender == owner);
_;
}
function transferOwnership(address newOwner) onlyOwner public {
owner = newOwner;
}
}
interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) public; }
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 notifies clients about the amount burnt
event Burn(address indexed from, uint256 value);
/**
* Constrctor 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;
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` in 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 in 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 in 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
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
Burn(_from, _value);
return true;
}
}
/******************************************/
/* ADVANCED TOKEN STARTS HERE */
/******************************************/
contract MyAdvancedToken is owned, TokenERC20 {
uint256 public sellPrice;
uint256 public buyPrice;
mapping (address => bool) public frozenAccount;
/* This generates a public event on the blockchain that will notify clients */
event FrozenFunds(address target, bool frozen);
/* Initializes contract with initial supply tokens to the creator of the contract */
function MyAdvancedToken(
uint256 initialSupply,
string tokenName,
string tokenSymbol
) TokenERC20(initialSupply, tokenName, tokenSymbol) public {}
/* Internal transfer, only can be called by this contract */
function _transfer(address _from, address _to, uint _value) internal {
require (_to != 0x0); // Prevent transfer to 0x0 address. Use burn() instead
require (balanceOf[_from] >= _value); // Check if the sender has enough
require (balanceOf[_to] + _value > balanceOf[_to]); // Check for overflows
require(!frozenAccount[_from]); // Check if sender is frozen
require(!frozenAccount[_to]); // Check if recipient is frozen
balanceOf[_from] -= _value; // Subtract from the sender
balanceOf[_to] += _value; // Add the same to the recipient
Transfer(_from, _to, _value);
}
/// @notice Create `mintedAmount` tokens and send it to `target`
/// @param target Address to receive the tokens
/// @param mintedAmount the amount of tokens it will receive
function mintToken(address target, uint256 mintedAmount) onlyOwner public {
balanceOf[target] += mintedAmount;
totalSupply += mintedAmount;
Transfer(0, this, mintedAmount);
Transfer(this, target, mintedAmount);
}
/// @notice `freeze? Prevent | Allow` `target` from sending & receiving tokens
/// @param target Address to be frozen
/// @param freeze either to freeze it or not
function freezeAccount(address target, bool freeze) onlyOwner public {
frozenAccount[target] = freeze;
FrozenFunds(target, freeze);
}
/// @notice Allow users to buy tokens for `newBuyPrice` eth and sell tokens for `newSellPrice` eth
/// @param newSellPrice Price the users can sell to the contract
/// @param newBuyPrice Price users can buy from the contract
function setPrices(uint256 newSellPrice, uint256 newBuyPrice) onlyOwner public {
sellPrice = newSellPrice;
buyPrice = newBuyPrice;
}
/// @notice Buy tokens from contract by sending ether
function buy() payable public {
uint amount = msg.value / buyPrice; // calculates the amount
_transfer(this, msg.sender, amount); // makes the transfers
}
/// @notice Sell `amount` tokens to contract
/// @param amount amount of tokens to be sold
function sell(uint256 amount) public {
require(this.balance >= amount * sellPrice); // checks if the contract has enough ether to buy
_transfer(msg.sender, this, amount); // makes the transfers
msg.sender.transfer(amount * sellPrice); // sends ether to the seller. It's important to do this last to avoid recursion attacks
}
}
它不会乘以10.它乘以（10 ^ 18）。该行用于处理自密实中的fixed point numbers are not yet supported以来的十进制偏移量。
ERC20令牌不需要使用18位小数（或根本不使用），但建议使用某种程度的精度，因为令牌的值可能会显着波动。在大多数示例中使用了图18，因为接收以太符合的合同使用wei级别的值（1 ether = 10 ^ 18 wei）。