今天，我们来讲讲如何编写一个实际可用，并且没有安全漏洞的生产级别的ERC20代币合约，当然很多人通过百度可以搜索到一堆发币的合约代码，但是大部分都是有安全漏洞的，达不到生产级别。6 f8 r( p- g1 |
废话不少，先上完整代码：
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1. pragma solidity ^0.4.24;
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2. library SafeMath {  /**( A1 r) Y3 `7 w$ ?
   
3.   * @dev Multiplies two numbers, throws on overflow.3 H* U0 s4 g' T2 D/ \) e
   
4.   */' o* p+ |& N7 r$ U! k$ |
   
5.   function mul(uint256 _a, uint256 _b) internal pure returns (uint256 c)
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6. {    if (_a == 0) {      return 0;
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7.     }- H; q, l6 B* t# w7 Z
   
8.     c = _a * _b;
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9.     assert(c / _a == _b);    return c;  i# F- H/ ~& g, f
   
10.   }  /**
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11.   * Integer division of two numbers, truncating the quotient.4 e0 p7 H1 _, U6 f: \
    
12.   */; R( A  J& g6 J  O# D% G
    
13.   function div(uint256 _a, uint256 _b) internal pure returns (uint256) {    return _a / _b;
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14.   }  /**2 i4 k- `; T5 j7 {) E# L6 w
    
15.   * Subtracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).- b. B  x* E8 y+ H
    
16.   */
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17.   function sub(uint256 _a, uint256 _b) internal pure returns (uint256) {
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18.     assert(_b = _a);    return c;
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19.   }
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20. }
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21. contract ERC20 {
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22.   uint256 public totalSupply;  function balanceOf(address _who)
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23.   public view returns (uint256); + h# t8 m4 E& v# w
    
24.    function allowance(address _owner, address _spender) public view returns (uint256); : O% z* g+ v+ E3 I1 s  O4 ^, W4 z2 G
    
25.     function transfer(address _to, uint256 _value) public returns (bool);  
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26.   function approve(address _spender, uint256 _value) public returns (bool);  
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27.     function transferFrom(address _from, address _to, uint256 _value) public returns (bool);  
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28.     event Transfer( address indexed from, address indexed to,  uint256 value);   I5 r7 ]2 |. J7 t5 P( U
    
29.      event Approval(address indexed owner, address indexed spender, uint256 value);  ) n0 ~8 J6 R% G2 n; l+ S+ Y2 I  ?
    
30.   event Burn(address indexed from, uint256 value);7 D; Q  @9 `3 N9 `4 g3 m, ^
    
31. }contract StandardToken is ERC20 {+ c4 `& a/ ]7 q/ D) N# ^
    
32.   using SafeMath for uint256;$ |" {0 a0 [" J2 m, j* `  X% [
    
33.   mapping(address => uint256) balances;8 T; K( Y+ R. m
    
34.   mapping (address => mapping (address => uint256)) internal allowed;  /**
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35.   * Gets the balance of the specified address.
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36.   * @param _owner The address to query the the balance of.
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37.   * @return An uint256 representing the amount owned by the passed address.
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38.   */
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39.   function balanceOf(address _owner) public view returns (uint256) 1 t: N: I+ C* d
    
40.      {    return balances[_owner];2 e1 d8 U& Y- \
    
41.   }  /**
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42.    *  Function to check the amount of tokens that an owner allowed to a spender.8 \9 g, F5 v, v1 a
    
43.    * @param _owner address The address which owns the funds.  s8 A6 H5 U1 q: R; }. _
    
44.    * @param _spender address The address which will spend the funds.4 y1 S* d0 V/ @
    
45.    * @return A uint256 specifying the amount of tokens still available for the spender.% m1 L! ^2 M: j
    
46.    */! X* X/ ^4 d8 e1 X: F1 ^
    
47.   function allowance(address _owner, address _spender) public view returns( u6 Z, I* y# I" \
    
48.       (uint256){    return allowed[_owner][_spender];) M' o& t; _5 [* i6 A" ?5 m1 h
    
49.   }  /**9 \0 E' s7 v( r5 [! g
    
50.   * Transfer token for a specified address( L0 W$ B$ [" y! M' E7 Q! f+ b
    
51.   * @param _to The address to transfer to.8 P% ^1 X! u; h* }. N; \! U' A
    
52.   * @param _value The amount to be transferred.
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53.   */
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54.   function transfer(address _to, uint256 _value) public returns
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55.       (bool) {    require(_value = oldValue) {
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56.       allowed[msg.sender][_spender] = 0;" I2 K$ u/ E  ]0 m5 S9 u! Q
    
57.     } else {
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58.       allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);4 w* h0 @6 ~) V) W8 L) U
    
59.     }1 o0 m8 r- O9 P, Z9 s3 {3 H
    
60.     emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);    return true;7 l9 w: z+ A* m) |) O
    
61.   }  
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62.    /**
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63.      * Destroy tokens. }6 V% Q: n+ Y- R* b  _. M
    
64.      *
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65.      * Remove `_value` tokens from the system irreversibly
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66.      *, Y6 p9 X1 t4 Z% N3 f# O0 g
    
67.      * @param _value the amount of money to burn
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68.      */
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69.     function burn(uint256 _value) public returns (bool success)
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70.           {        require(balances[msg.sender] >= _value);   7 T- @; w% B2 S" Y
    
71.         balances[msg.sender] = balances[msg.sender].sub(_value);         
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72.         totalSupply = totalSupply.sub(_value);                     
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73.         emit Burn(msg.sender, _value);        return true;
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74.     }    /**
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75.      * Destroy tokens from other account
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76.      *
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77.      * Remove `_value` tokens from the system irreversibly on behalf of `_from`.
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78.      *. U5 g4 g" h0 {; i; s, b' t9 h* d
    
79.      * @param _from the address of the sender% Y# H! S. T- }: I" x( s( q: f6 l
    
80.      * @param _value the amount of money to burn
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81.      */2 l% t& P; a' V/ l8 E% ^
    
82.     function burnFrom(address _from, uint256 _value) public returns (bool success) % b2 [$ d' \$ }
    
83.           {        require(balances[_from] >= _value);                6 U% a* B: d- W! Y
    
84.         require(_value

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+ D# P6 u/ \+ z% s" J$ p0 n这些代码是什么意思呢？# Y4 g) m8 ?" X
一、ERC20（EIP-20）说明
. t, `; o* o5 m: ^" K2 ~ERC20是一个标准的token接口规范：A standard interface for tokens
& o2 g7 F5 B0 R( h该接口的官网说明在下面的链接：https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md2 L7 J, F& E2 W: X. q+ E
我们来简单介绍下这个接口规范，规范里面定义了9个方法和2个事件
  Y) E" f/ `; E2 R8 E% N5 v9个方法包括：
$ O& D8 D# z9 J( P% K3 c2 ?9 L/ o返回token的名字; Y, I" @0 P- c6 _9 G
function name() view returns (string name)5 P9 m( ~( i% F$ u; [$ \
返回token的代码
* E2 G6 R8 V7 O) \  R2 j6 rfunction symbol() view returns (string symbol)6 l4 X1 J2 {- p+ j
返回token的小数点位数5 U. P$ S2 L9 m, h  \  g
function decimals() view returns (uint8 decimals)$ }; k- A2 i/ P* B  `
返回供应总量
6 ~( g3 B/ t5 B: G+ Z7 Dunction totalSupply() view returns (uint256 totalSupply)
( W# t8 [. B& I( d5 Z- O1 q8 P, W查询某个地址的余额4 q7 ]6 {. U+ b
function balanceOf(address _owner) view returns (uint256 balance)3 p9 {4 [9 M2 s1 ~" U: O
给某个地址转账，如果余额不足，该方法必须抛出异常而不是返回false
) ]0 c! g0 T  |- S2 e9 G+ W4 f2 \function transfer(address _to, uint256 _value) returns (bool success)
$ _1 ^- i9 d7 K) G% A% @从from地址转账到to地址，该方法用于委托给其他合约代理你转账
  T/ \* d; Y$ B+ T% a- Nfunction transferFrom(address _from, address _to, uint256 _value) returns (bool success)
5 ^4 z8 W0 k5 M& G& i; i允许多次从您的帐户委托到_spender地址，最高_value金额。如果再次调用此函数，则会覆盖当前允许值_value
( V4 p. X7 n3 Xfunction approve(address _spender, uint256 _value) returns (bool success)* t- t' k0 X( d1 b2 t
返回_spender仍允许退出的金额_owner
# r7 z! [. z0 _& O9 Hfunction allowance(address _owner, address _spender) view returns (uint256 remaining)6 I3 q" u2 {1 N+ Y5 B
2个事件包括：
& L; `" t+ [/ Y7 D3 u转移令牌时必须触发，包括零值转移，注意：创建新token的合约应该触发Transfer事件，即从_from地址设置为0x0创建token的时候
: E; s$ a$ T4 Zevent Transfer(address indexed _from, address indexed _to, uint256 _value)
! R8 ]9 `2 R/ t6 P- W委托转账必须触发
+ e! U  H0 r$ X9 [9 O6 b# pevent Approval(address indexed _owner, address indexed _spender, uint256 _value), N; B2 \2 ^) f9 x0 q
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二、代码解释
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; O0 X4 J/ _+ h4 z代码包括几部分：7 N0 p& F* r% }, O" @7 e+ b
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安全的数学计算库' l5 Z! b  M6 b8 n. X

6 D$ Q( U0 s6 A9 H/ {+ I, g8 vcontract类 ERC20，主要针对ERC20规范定义方法和事件/ c+ |  L( _! x) J2 I+ a
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contract类StandardToken继承ERC20，定义具体的方法实现, ]; T# n( d" n

5 |& G! l$ w( W1 m4 ^  v+ b+ Xcontract 类MyTokenERC20集成StandardToken，定义名词，代号，总供应量和创建token