I'm given a list of timestamps (suppose we have a ready-made std::vector<std::string>) in a string format of a kind std::vector<std::string> = {"12:27:37.740002", "19:37:17.314002", "20:00:07.140902",...}. No dates, no timezones. What would be a preferable way to parse these strings to some kind of C type (std::chrono::time_point ?) to be able to perform some comparisons and sorting later.

For example: compare value, which was parsed from "20:00:07.140902" and value, was parsed from "20:00:07.000000".

C 17 is ok, but I can't use any third-party library (Boost, Date etc). Keeping microseconds precision essential.

CodePudding user response：

You can build this functionality completly with C standard library functionality. For parsing the string use std::regex. For time related datatypes use std::chrono

Example :

#include <stdexcept>
#include <regex>
#include <chrono>
#include <iostream>

auto parse_to_timepoint(const std::string& input)
{
    // setup a regular expression to parse the input string
    // https://regex101.com/
    // each part between () is a group and will end up in the match
    // [0-2] will match any character from 0 to 2 etc..
    // [0-9]{6} will match exactly 6 digits
    static const std::regex rx{ "([0-2][0-9]):([0-5][0-9]):([0-5][0-9])\\.([0-9]{6})" };
    std::smatch match;

    if (!std::regex_search(input, match, rx))
    {
        throw std::invalid_argument("input string is not a valid time string");
    }

    // convert each matched group to the corresponding value
    // note match[0] is the complete matched string by the regular expression
    // we only need the groups which start at index 1
    const auto& hours = std::stoul(match[1]);
    const auto& minutes = std::stoul(match[2]);
    const auto& seconds = std::stoul(match[3]);
    const auto& microseconds = std::stoul(match[4]);
    
    // build up a duration
    std::chrono::high_resolution_clock::duration duration{};
    duration  = std::chrono::hours(hours);
    duration  = std::chrono::minutes(minutes);
    duration  = std::chrono::seconds(seconds);
    duration  = std::chrono::microseconds(microseconds);

    // then return a time_point (note this will not help you with correctly handling day boundaries)
    // since there is no date in the input string
    return std::chrono::high_resolution_clock::time_point{ duration };
}

int main()
{
    std::string input1{ "20:00:07.140902" };
    std::string input2{ "20:00:07.000000" };

    auto tp1 = parse_to_timepoint(input1);
    auto tp2 = parse_to_timepoint(input2);

    std::cout << "start time = " << ((tp1 < tp2) ? input1 : input2) << "\n";
    std::cout << "end time = " << ((tp1 >= tp2) ? input1 : input2) << "\n";

    return 0;
}