C++: Getting the Current Time as a W3C UTC Time String

Question

How can I get the current time as a W3C UTC time string as documented at W3C Date and Time Formats (Profile of ISO 8601)?

Specifically, here is the format I am after:

yyyy-mm-ddThh:mm:ssZ

Example:

2013-05-24T20:07:47Z

Note: I am using Visual Studio 2010.

Answer 1

Here is my solution. Visual Studio 2010 references: time(), gmtime_s()

#include <iomanip>
#include <sstream>
#include <time.h>

/**
 * Get the current time as a W3C UTC time string.
 *
 * @return A time string; the empty string if something goes wrong.
 */
std::string GetUTCTimeString(void)
{
    time_t seconds_since_the_epoch;
    struct tm tm_struct;
    errno_t err;
    std::ostringstream buf;

    // Return the time as seconds elapsed since midnight, January 1, 1970,
    // or -1 in the case of an error.
    time(&seconds_since_the_epoch);

    if (seconds_since_the_epoch == -1) {
        return "";
    }

    // Convert the time in seconds to the time structure.
    err = gmtime_s(&tm_struct, &seconds_since_the_epoch);

    if (err) {
        return "";
    }

    // Format the structure as a W3C UTC date/time string with the special
    // UTC designator 'Z'.
    buf
        <<        std::setw(4) << std::setfill('0') << tm_struct.tm_year + 1900
        << "-" << std::setw(2) << std::setfill('0') << tm_struct.tm_mon + 1
        << "-" << std::setw(2) << std::setfill('0') << tm_struct.tm_mday
        << "T" << std::setw(2) << std::setfill('0') << tm_struct.tm_hour
        << ":" << std::setw(2) << std::setfill('0') << tm_struct.tm_min
        << ":" << std::setw(2) << std::setfill('0') << tm_struct.tm_sec
        << "Z";

    return buf.str();
}