小明今天繼續完成的是用戶存提 ERC20 代幣的功能：

User 用戶功能

• 存入 ERC20 代幣
  將用戶錢包中的 ERC20 代幣存入交易所

function depositToken(string symbolName, uint amount) public {
    uint8 symbolNameIndex = getSymbolIndexOrThrow(symbolName);
    require(tokens[symbolNameIndex].tokenContract != address(0));

    ERC20Interface token = ERC20Interface(tokens[symbolNameIndex].tokenContract);

    require(token.transferFrom(msg.sender, address(this), amount) == true);
    require(tokenBalanceForAddress[msg.sender][symbolNameIndex] + amount >= tokenBalanceForAddress[msg.sender][symbolNameIndex]);
    tokenBalanceForAddress[msg.sender][symbolNameIndex] += amount;
    emit DepositForTokenReceived(msg.sender, symbolNameIndex, amount, now);
}

• 提領 ERC20 代幣
  將用戶在交易所的 ERC20 代幣領出到用戶錢包

function withdrawToken(string symbolName, uint amount) public {
    uint8 symbolNameIndex = getSymbolIndexOrThrow(symbolName);
    require(tokens[symbolNameIndex].tokenContract != address(0));

    ERC20Interface token = ERC20Interface(tokens[symbolNameIndex].tokenContract);

    require(tokenBalanceForAddress[msg.sender][symbolNameIndex] - amount >= 0);
    require(tokenBalanceForAddress[msg.sender][symbolNameIndex] - amount <= tokenBalanceForAddress[msg.sender][symbolNameIndex]);

    tokenBalanceForAddress[msg.sender][symbolNameIndex] -= amount;
    require(token.transfer(msg.sender, amount) == true);
    emit WithdrawalToken(msg.sender, symbolNameIndex, amount, now);
}

• 檢視 ERC20 代幣餘額
  取得用戶 ERC20 代幣的餘額

function getBalance(string symbolName) view public returns (uint) {
    uint8 symbolNameIndex = getSymbolIndexOrThrow(symbolName);
    return tokenBalanceForAddress[msg.sender][symbolNameIndex];
}

本文同時發佈於作者部落格：https://www.bdetw.com/blog

想找區塊鏈人才或想學習區塊鏈知識的夥伴。歡迎參加社群小聚，一起來輕鬆交流、互相學習成長、認識新朋友、發現新機會！
　
台北區塊鏈社群
https://bitlly.co/Q4dIK
　
BDE 區塊鏈學院 - 提供專業的區塊鏈培訓與顧問服務。
https://bitlly.co/mbDwX