ERC20代码详解

1、流程图

2、ERC20代码详解

    1）、基本合约提供总发行量，余额，交易转账函数以及转账事件

2）、SafeMath加减乘除library 库

library SafeMath {

  /**

  * @dev Multiplies two numbers, throws on overflow.

  */

  function mul(uint256 a, uint256 b) internal pure returns (uint256) {

    if (a == 0) {

      return 0;

    }

    uint256 c = a * b;

    assert(c / a == b);

    return c;

  }

  /**

  * @dev Integer division of two numbers, truncating the quotient.

  */

  function div(uint256 a, uint256 b) internal pure returns (uint256) {

    // assert(b > 0); // Solidity automatically throws when dividing by 0

    uint256 c = a / b;

    // assert(a == b * c + a % b); // There is no case in which this doesn't hold

    return c;

  }

  /**

  * @dev Substracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).

  */

  function sub(uint256 a, uint256 b) internal pure returns (uint256) {

    assert(b <= a);

    return a - b;

  }

  /**

  * @dev Adds two numbers, throws on overflow.

  */

  function add(uint256 a, uint256 b) internal pure returns (uint256) {

    uint256 c = a + b;

    assert(c >= a);

    return c;

  }

}

 3）、ERC20合约提供允许转账金额查询，从A账户到B账户的交易，授权A-》B的转账以及授权事件

4）、实现ERC20Basic合约的function

5）、实现ERC20, BasicToken合约