5G IOT Space chain

pragma solidity ^0.5.1;
 //区块链技术服务+手机号/微信：19933104907 
contract ERC20Standard {
    using SafeMath for uint256;
	uint256 public totalSupply;
	string public name;
	uint8 public decimals;
	string public symbol;
	address public owner;

	mapping (address => uint256) balances;
	mapping (address => mapping (address => uint256)) allowed;

   constructor(uint256 _totalSupply, string memory _symbol, string memory _name, uint8 _decimals) public {
		symbol = _symbol;
		name = _name;
        decimals = _decimals;
		owner = msg.sender;
        totalSupply = SafeMath.mul(_totalSupply ,(10 ** uint256(decimals)));
        balances[owner] = totalSupply;
  }
	//Fix for short address attack against ERC20
	modifier onlyPayloadSize(uint size) {
		assert(msg.data.length == SafeMath.add(size,4));
		_;
	} 

	function balanceOf(address _owner) view public returns (uint256) {
		return balances[_owner];
	}

	function transfer(address _recipient, uint256 _value) onlyPayloadSize(2*32) public returns(bool){
	    require(_recipient!=address(0));
		require(balances[msg.sender] >= _value && _value >= 0);
	    require(balances[_recipient].add(_value)>= balances[_recipient]);
	    balances[msg.sender] = balances[msg.sender].sub(_value) ;
	    balances[_recipient] = balances[_recipient].add(_value) ;
	    emit Transfer(msg.sender, _recipient, _value);  
	    return true;
    }

	function transferFrom(address _from, address _to, uint256 _value) public returns(bool){
	    require(_to!=address(0));
		require(balances[_from] >= _value && allowed[_from][msg.sender] >= _value && _value >= 0);
		require(balances[_to].add(_value) >= balances[_to]);
        balances[_to] = balances[_to].add(_value);
        balances[_from] = balances[_from].sub(_value) ;
        allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value) ;
        emit Transfer(_from, _to, _value);
        return true;
    }

	function approve(address _spender, uint256 _value) public returns(bool){
	    require((_value==0)||(allowed[msg.sender][_spender]==0));
    	allowed[msg.sender][_spender] = _value;
		emit Approval(msg.sender, _spender, _value);
		return true;
	}

	function allowance(address _owner, address _spender) view public returns (uint256) {
		return allowed[_owner][_spender];
	}

	//Event which is triggered to log all transfers to this contract's event log
	event Transfer(
		address indexed _from,
		address indexed _to,
		uint256 _value
		);
		
	//Event which is triggered whenever an owner approves a new allowance for a spender.
	event Approval(
		address indexed _owner,
		address indexed _spender,
		uint256 _value
		);

}
library SafeMath {
    /**
     * @dev Multiplies two unsigned integers, reverts on overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Integer division of two unsigned integers truncating the quotient, reverts on division by zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, "SafeMath: division by zero");
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Subtracts two unsigned integers, reverts on overflow (i.e. if subtrahend is greater than minuend).
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a, "SafeMath: subtraction overflow");
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Adds two unsigned integers, reverts on overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Divides two unsigned integers and returns the remainder (unsigned integer modulo),
     * reverts when dividing by zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b != 0, "SafeMath: modulo by zero");
        return a % b;
    }
}

{
  "compilationTarget": {
    "ERC20Standard.sol": "ERC20Standard"
  },
  "evmVersion": "byzantium",
  "libraries": {},
  "optimizer": {
    "enabled": false,
    "runs": 200
  },
  "remappings": []
}