If I have a single string storing both Day and Time in the format "mm/dd-hh:mm" how can I create the string of two days ahead?

CodePudding user response：

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 (e.g. "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