String representation of time_t?

Question

time_t seconds;
time(&seconds);

cout << seconds << endl;

This gives me a timestamp. How can I get that epoch date into a string?

std::string s = seconds;

does not work

Thanks, Noah

P.S. It's really much easier in ruby!:

>> Time.now.to_i.to_s
=> "1245089994"

Answer 1

Try 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.

Answer 2

Standard C++ does not have any time/date functions of its own - you need to use the C localtime and related functions.

Answer 3

Try this if you want to have the time in a readable string:

#include "ctime"

time_t now = time(NULL);
struct tm * ptm = localtime(&now);
char buffer[32];
// Format: Mo, 15.06.2009 20:20:00
strftime (buffer, 32, "%a, %d.%m.%Y %H:%M:%S", ptm);

For further reference of strftime() check out cplusplus.com

Answer 4

the function "ctime()" will convert a time to a string. If you want to control the way its printed, use "strftime". However, strftime() takes an argument of "struct tm". Use "localtime()" to convert the time_t 32 bit integer to a struct tm.

Answer 5

There are a myriad of ways in which you might want to format time (depending on the time zone, how you want to display it, etc.), so you can't simply implicitly convert a time_t to a string.

The C way is to use ctime or to use strftime plus either localtime or gmtime.

If you want a more C++-like way of performing the conversion, you can investigate the Boost.DateTime library.

Answer 6

The C++ way is to use stringstream.

The C way is to use snprintf() to format the number:

 char buf[16];
 snprintf(buf, 16, "%lu", time(NULL));