Output date string in C++

Iterate days

	/// iterate from fromD(like "2014-04-02") to toD("2014-05-02")
	std::string tpStr = fromD;
	do {
		//std::cout << tpStr << std::endl;
		ParseIntoUserInfoDB(tpStr, root, order);

		std::tm tm;
		std::stringstream ss(tpStr + " 0:0:1");
		ss >> std::get_time(&tm, "%Y-%m-%d %H:%M:%S");
		auto tp = std::chrono::system_clock::from_time_t(std::mktime(&tm));

		tp += std::chrono::hours(24);

		auto in_time_t = std::chrono::system_clock::to_time_t(tp);
		std::stringstream ssTp;
		ssTp << std::put_time(std::localtime(&in_time_t), "%Y-%m-%d");
		tpStr = ssTp.str();

	} while (tpStr != toD);

OutputDateString.cpp

#include <string>
#include <sstream>
#include <chrono>
#include <iomanip>

std::string GetDate(const char* argv)
{
	std::string arg(argv);
	if (pystring::lower(arg) == "today")
	{
		auto now = std::chrono::system_clock::now();
		auto in_time_t = std::chrono::system_clock::to_time_t(now);

		std::stringstream ss;
		ss << std::put_time(std::localtime(&in_time_t), "%Y-%m-%d");
		return ss.str();
	}

	return arg;
}