String representation of time_t? - c++

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

Answer 1

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().

Answer 2

Try this if you want to have the time in a readable string:
#include <ctime>
std::time_t now = std::time(NULL);
std::tm * ptm = std::localtime(&now);
char buffer[32];
// Format: Mo, 15.06.2009 20:20:00
std::strftime(buffer, 32, "%a, %d.%m.%Y %H:%M:%S", ptm);
For further reference of strftime() check out cppreference.com

Answer 3

The top answer here does not work for me.
See the following examples demonstrating both the stringstream and lexical_cast answers as suggested:
#include <iostream>
#include <sstream>
int main(int argc, char** argv){
const char *time_details = "2017-01-27 06:35:12";
struct tm tm;
strptime(time_details, "%Y-%m-%d %H:%M:%S", &tm);
time_t t = mktime(&tm);
std::stringstream stream;
stream << t;
std::cout << t << "/" << stream.str() << std::endl;
}
Output: 1485498912/1485498912
Found here
#include <boost/lexical_cast.hpp>
#include <string>
int main(){
const char *time_details = "2017-01-27 06:35:12";
struct tm tm;
strptime(time_details, "%Y-%m-%d %H:%M:%S", &tm);
time_t t = mktime(&tm);
std::string ts = boost::lexical_cast<std::string>(t);
std::cout << t << "/" << ts << std::endl;
return 0;
}
Output: 1485498912/1485498912
Found: here
The 2nd highest rated solution works locally:
#include <iostream>
#include <string>
#include <ctime>
int main(){
const char *time_details = "2017-01-27 06:35:12";
struct tm tm;
strptime(time_details, "%Y-%m-%d %H:%M:%S", &tm);
time_t t = mktime(&tm);
std::tm * ptm = std::localtime(&t);
char buffer[32];
std::strftime(buffer, 32, "%Y-%m-%d %H:%M:%S", ptm);
std::cout << t << "/" << buffer;
}
Output: 1485498912/2017-01-27 06:35:12
Found: here

Answer 4

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

Answer 5

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 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));

Answer 7

Here's my formatter -- comments welcome. This q seemed like it had the most help getting me to my a so posting for anyone else who may be looking for the same.
#include <iostream>
#include "Parser.h"
#include <string>
#include <memory>
#include <ctime>
#include <chrono>
#include <iomanip>
#include <thread>
using namespace std;
string to_yyyyMMddHHmmssffffff();
string to_yyyyMMddHHmmssffffff() {
using namespace std::chrono;
high_resolution_clock::time_point pointInTime = high_resolution_clock::now();
std::time_t now_c = std::chrono::system_clock::to_time_t(pointInTime);
microseconds micros = duration_cast<microseconds>(pointInTime.time_since_epoch());
std::size_t fractional_microseconds = micros.count() % 1'000'000;
std:stringstream microstream;
microstream << "00000" << fractional_microseconds;
string formatted = microstream.str();
int index = formatted.length() - 6;
formatted = formatted.substr(index);
std::stringstream dateStream;
dateStream << std::put_time(std::localtime(&now_c), "%F %T") << "." << formatted;
formatted = dateStream.str();
return formatted;
}

Answer 8

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 9

localtime did not work for me. I used localtime_s:
struct tm buf;
char dateString[26];
time_t time = time(nullptr);
localtime_s(&buf, &time);
asctime_s(dateString, 26, &buf);