C++ Cookbook

5.2. Formatting a Date/Time as a String

Problem

You want to convert a date and/or time to a formatted string.

Solution

You can use the time_put template class from the <locale> header, as shown in Example 5-4.

Example 5-4. Formatting a datetime string

#include <iostream>
#include <cstdlib>
#include <ctime>
#include <cstring>
#include <string>
#include <stdexcept>
#include <iterator>
#include <sstream>

using namespace std;

ostream& formatDateTime(ostream& out, const tm& t, const char* fmt) {
  const time_put<char>& dateWriter = use_facet<time_put<char> >(out.getloc());
  int n = strlen(fmt);
  if (dateWriter.put(out, out, ' ', &t, fmt, fmt + n).failed()) {
    throw runtime_error("failure to format date time");
  }
  return out;
}

string dateTimeToString(const tm& t, const char* format) {
  stringstream s;
  formatDateTime(s, t, format);
  return s.str();
}

tm now() {
  time_t now = time(0);
  return *localtime(&now);
}

int main()
{
  try {
    string s = dateTimeToString(now(), "%A %B, %d %Y %I:%M%p");
    cout << s << endl;
    s = dateTimeToString(now(), "%Y-%m-%d %H:%M:%S");
    cout << s << endl;
  }
  catch(...) {
    cerr << "failed to format date time" << endl;
    return EXIT_FAILURE;
  }
  return EXIT_SUCCESS;
}

Output of the program in Example 5-4 will resemble the following, depending on your local settings:

Sunday July, 24 2005 05:48PM
2005-07-24 17:48:11

Discussion

The time_put member function put uses a formatting string specifier like the C printf function format string. Characters are output to the buffer as they appear in ...