跟我一起阅读并修复源码（3：编译工程，源码分析）之六_transferhelper: transfer from failed

在上一章跟我一起阅读并修复某知名DEX交易所源码（3：编译工程，源码分析）之五_lixiaodog的博客-CSDN博客

中我们详细分析了 contract MdexPair的源码，本章将继续编译的进程，来吧，少年，出发吧！！

输入编译命令truffle compile

project:/contracts/mainnet/CoinChef.sol:48:43: TypeError: Operator ** not compatible with types int_const 100 and int_const 1000000000000000000
    uint256 public constant mdxPerBlock = 100 ** 1e18;

**运算符无法用于这两个常数，我认为应该是写错了，修改为:

uint256 public constant mdxPerBlock = 100*10**18;

每区块产量100个。如果是100**1E18 ,是个多大的数大家可以想像。

再次编译，如下图：

> Duplicate contract names found for TransferHelper.
> This can cause errors and unknown behavior. Please rename one of your contracts.
 
> Duplicate contract names found for IWHT.
> This can cause errors and unknown behavior. Please rename one of your contracts.
 
> Duplicate contract names found for TransferHelper.
> This can cause errors and unknown behavior. Please rename one of your contracts.
 
> Duplicate contract names found for MdxToken.
> This can cause errors and unknown behavior. Please rename one of your contracts.
 
> Duplicate contract names found for SafeMath.
> This can cause errors and unknown behavior. Please rename one of your contracts.

 合约名TransferHelper冲突了。在全局范围内搜索，如下图：

在 C:\work\blockchain\Mdex\contracts\assets\Airdrop.sol
  9,9: library TransferHelper {
  13,77:         require(success && (data.length == 0 || abi.decode(data, (bool))), 'TransferHelper: APPROVE_FAILED');
  19,77:         require(success && (data.length == 0 || abi.decode(data, (bool))), 'TransferHelper: TRANSFER_FAILED');
  25,77:         require(success && (data.length == 0 || abi.decode(data, (bool))), 'TransferHelper: TRANSFER_FROM_FAILED');
  87,9:         TransferHelper.safeTransferFrom(address(wht), msg.sender, address(this), _whtAmount);

与

C:\work\blockchain\Mdex\contracts\assets\AirdropMDX.sol
  10,9: library TransferHelper {
  14,77:         require(success && (data.length == 0 || abi.decode(data, (bool))), 'TransferHelper: APPROVE_FAILED');
  20,77:         require(success && (data.length == 0 || abi.decode(data, (bool))), 'TransferHelper: TRANSFER_FAILED');
  26,77:         require(success && (data.length == 0 || abi.decode(data, (bool))), 'TransferHelper: TRANSFER_FROM_FAILED');
  83,9:         TransferHelper.safeTransferFrom(mdx, msg.sender, address(this), _mdxAmount);

发现了同名定义，此时我们需要决定修改哪个定义，以解决冲突，通过对比我们发现这三处定义是一模一样的，所以我直接把这个库合并为一个库，在library新建文件TransferHelper.sol，如下图

同时删除其它两处的相关定义，并添加import "library/TransferHelper.sol";

pragma solidity ^0.6.0;
library TransferHelper {
    function safeApprove(address token, address to, uint value) internal {
        // bytes4(keccak256(bytes('approve(address,uint256)')));
        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(0x095ea7b3, to, value));
        require(success && (data.length == 0 || abi.decode(data, (bool))), 'TransferHelper: APPROVE_FAILED');
    }
 
    function safeTransfer(address token, address to, uint value) internal {
        // bytes4(keccak256(bytes('transfer(address,uint256)')));
        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(0xa9059cbb, to, value));
        require(success && (data.length == 0 || abi.decode(data, (bool))), 'TransferHelper: TRANSFER_FAILED');
    }
 
    function safeTransferFrom(address token, address from, address to, uint value) internal {
        // bytes4(keccak256(bytes('transferFrom(address,address,uint256)')));
        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(0x23b872dd, from, to, value));
        require(success && (data.length == 0 || abi.decode(data, (bool))), 'TransferHelper: TRANSFER_FROM_FAILED');
    }
    function safeTransferETH(address to, uint value) internal {
        (bool success,) = to.call{value : value}(new bytes(0));
        require(success, 'TransferHelper: ETH_TRANSFER_FAILED');
    }
}

搜索library SafeMath

 在oracle.sol中我们发的safemath只有定义，但实际上在这个文件中并未有实际使用，所以注释掉safeMath的定义和  //using SafeMathUint for uint;

搜索MdxToken,结果如下图：

我们发现在MdxToken.sol中的定义并未被引用过，全部注释掉 

搜索IWHT，如下图

 注释Airdrop.sol的定义，并在interface下新建文件IWHT.SOL,代码：

interface IWHT {
    function balanceOf(address owner) external view returns (uint);
    function deposit() external payable;
 
    function transfer(address to, uint value) external returns (bool);
 
    function withdraw(uint) external;
}

在上面两个文件中加入：import "../interface/IWHT.sol"; 

再次编译，结果如下图：

编译通过，至此，所有的编译问题已经全部解决，在下一章跟我一起阅读并修复某知名DEX交易所源码（4：部署工程，源码分析）_lixiaodog的博客-CSDN博客中，我们将会尝试布署MDEX至本地测试环境。敬请期待！！！