比较 C++ 中的 DayTime 字符串

Question

如果我有一个以“mm/dd-hh:mm”格式存储日期和时间的字符串，我该如何创建提前两天的字符串？

Answer 1

You can use Howard Hinnant's date library.

1. First of all, fix the input string by adding something that could be parsed as a year, and not a leap year (eg "01/" ), so that date::from_stream parses the date and time input string into a time point ( tp1 ) correctly.
2. Get the date two days ahead of tp1 , that is, tp1 + days{2} .
3. Format the new date back to a string by using date::format .

[Demo]

#include <chrono>
#include <date/date.h>
#include <iostream>  // cout
#include <sstream>  // istringstream
#include <string>

std::string two_days_ahead(const std::string& dt) {
    auto fixed_dt{std::string{"01/"} + dt};
    std::istringstream iss{fixed_dt};
    date::sys_time<std::chrono::minutes> tp1{};
    date::from_stream(iss, "%y/%m/%d-%H:%M", tp1);
    return date::format("%m/%d-%H:%M", tp1 + date::days{2});
}

int main() {
    std::cout << two_days_ahead("10/30-09:50") << "\n";
}

// Input: "10/30-09:50"
// Output: 11/01-09:50