Date/Time Conversion: String Representation to Time_T

Date/time conversion: string representation to time_t

Use strptime() to parse the time into a struct tm, then use mktime() to convert to a time_t.

How to convert a string variable containing time to time_t type in c++?

You can use strptime(3) to parse the time, and then mktime(3) to convert it to a time_t:

const char *time_details = "16:35:12";
struct tm tm;
strptime(time_details, "%H:%M:%S", &tm);
time_t t = mktime(&tm);  // t is now your desired time_t

String representation of time_t?

Try std::stringstream.

#include <string>
#include <sstream>

std::stringstream ss;
ss << seconds;
std::string ts = ss.str();

A nice wrapper around the above technique is Boost's lexical_cast:

#include <boost/lexical_cast.hpp>
#include <string>

std::string ts = boost::lexical_cast<std::string>(seconds);

And for questions like this, I'm fond of linking The String Formatters of Manor Farm by Herb Sutter.

UPDATE:

With C++11, use to_string().

How to parse date/time from string?

Although I don't know how to format a single-digit month input in boost, I can do it after the two-digit edit:

#include <iostream>
#include <boost/date_time.hpp>
namespace bt = boost::posix_time;
const std::locale formats[] = {
std::locale(std::locale::classic(),new bt::time_input_facet("%Y-%m-%d %H:%M:%S")),
std::locale(std::locale::classic(),new bt::time_input_facet("%Y/%m/%d %H:%M:%S")),
std::locale(std::locale::classic(),new bt::time_input_facet("%d.%m.%Y %H:%M:%S")),
std::locale(std::locale::classic(),new bt::time_input_facet("%Y-%m-%d"))};
const size_t formats_n = sizeof(formats)/sizeof(formats[0]);

std::time_t pt_to_time_t(const bt::ptime& pt)
{
    bt::ptime timet_start(boost::gregorian::date(1970,1,1));
    bt::time_duration diff = pt - timet_start;
    return diff.ticks()/bt::time_duration::rep_type::ticks_per_second;

}
void seconds_from_epoch(const std::string& s)
{
    bt::ptime pt;
    for(size_t i=0; i<formats_n; ++i)
    {
        std::istringstream is(s);
        is.imbue(formats[i]);
        is >> pt;
        if(pt != bt::ptime()) break;
    }
    std::cout << " ptime is " << pt << '\n';
    std::cout << " seconds from epoch are " << pt_to_time_t(pt) << '\n';
}
int main()
{
    seconds_from_epoch("2004-03-21 12:45:33");
    seconds_from_epoch("2004/03/21 12:45:33");
    seconds_from_epoch("23.09.2004 04:12:21");
    seconds_from_epoch("2003-02-11");
}

note that the seconds-from-epoch output will be assuming the date was in UTC:

~ $ ./test | head -2
ptime is 2004-Mar-21 12:45:33
seconds from epoch are 1079873133
~ $ date -d @1079873133
Sun Mar 21 07:45:33 EST 2004

You could probably use boost::posix_time::c_time::localtime() from #include <boost/date_time/c_time.hpp> to get this conversion done assuming the input is in the current time zone, but it is rather inconsistent: for me, for example, the result will be different between today and next month, when daylight saving ends.

C++ Converting a Datetime String to Epoch Cleanly

See: Date/time conversion: string representation to time_t

And: [Boost-users] [date_time] So how come there isn't a to_time_t helper func?

So, apparently something like this should work:

#include <boost/date_time/posix_time/posix_time.hpp>
using namespace boost::posix_time;

std::string ts("2002-01-20 23:59:59");
ptime t(time_from_string(ts));
ptime start(gregorian::date(1970,1,1)); 
time_duration dur = t - start; 
time_t epoch = dur.total_seconds();    

But I don't think it's much cleaner than Rob's suggestion: use sscanf to parse the data into a struct tm and then call mktime.

C string representation of time_t

If the aim is to store the value of time_t in a char array, you can use sprintf as:

char strTime[50];
sprintf(strTime,"%d",Time_Epoch);

Convert date and time numbers to time_t AND specify the timezone

It makes me want to throw up in my mouth a little bit, but you could convert it to a string with strftime(), replace the timezone in the string and then convert it back with strptime() and into a time_t with mktime(). In detail:

#ifdef UGLY_HACK_VOIDS_WARRANTY
time_t convert_time(const struct tm* tm)
{
    const size_t BUF_SIZE=256;
    char buffer[BUF_SIZE];
    strftime(buffer,256,"%F %H:%M:%S %z", tm);
    strncpy(&buffer[20], "+0001", 5); // +0001 is the time-zone offset from UTC in hours
    struct tm newtime = {0};
    strptime(buffer, "%F %H:%M:%S %z", &newtime);
    return mktime(&newtime);
}
#endif

However, I would highly recommend you convince the powers that be that boost is an option after all. Boost has great support for custom timezones. There are other libraries that do this elegantly as well.

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