Solidity字符串拼接实现oraclize动态查询

solidity本身没有字符串拼接功能，但是如果你恰巧要用oraclize api，那么可以使用oraclize api中的字符串拼接方法（strConcat）。之所以oraclize api里会有strConcat方法，我想是因为方便用户实现动态查询。

//auther: shiming liu
pragma solidity ^0.4.21;

import "github.com/oraclize/ethereum-api/oraclizeAPI.sol";

contract strConcatContract is usingOraclize{
    string urlPrefix = "https://api.iextrading.com/1.0/stock/";
    string stock_name = "aapl";
    string underline = "_";
    uint date = 3100;
    string PRICE = "/price";
    string public url = strConcat(urlPrefix,stock_name,underline,uint2str(date),PRICE); // "https://api.iextrading.com/1.0/stock/aapl_3100/price"
}