Member Avatar for spanigrahi_situ

HI All,
Ant Unix method or C++ method is there to convert unix time stamp to system time stamp.The input is ULONG and out put should be in string.


u can intimate to <email snipped>
Any help is appreciated in advance.

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A Unix timestamp like 1227806311 is the count of seconds since 1970-01-01 00:00:00 UTC. To print it as a string, convert to struct tm and format with strftime. Use gmtime* for UTC/GMT (what you asked in post #6) or localtime* for your machine’s timezone. For your example, 1227806311 -> 27/11/2008 17 18 31 UTC. was right that the C standard does not mandate an epoch, but on POSIX and Windows you can treat time_t as seconds since the Unix epoch in practice.

#include <time.h>
#include <stdio.h>

static int unix_to_string(unsigned long secs, int use_utc,
                          char *out, size_t outsz)
{
    time_t t = (time_t)secs;
    struct tm tmv;

#if defined(_WIN32)
    if (use_utc) { if (gmtime_s(&tmv, &t)) return -1; }
    else         { if (localtime_s(&tmv, &t)) return -1; }
#else
    if (use_utc) { if (!gmtime_r(&t, &tmv)) return -1; }
    else         { if (!localtime_r(&t, &tmv)) return -1; }
#endif

    return strftime(out, outsz, "%d/%m/%Y %H %M %S", &tmv) ? 0 : -1;
}

int main(void) {
    char buf[32];
    if (unix_to_string(1227806311UL, 1, buf, sizeof buf) == 0)  // UTC/GMT
        puts(buf);
    if (unix_to_string(1227806311UL, 0, buf, sizeof buf) == 0)  // local time
        puts(buf);
}

Tips:

  • Make sure your input is in seconds, not milliseconds. If it is ms, divide by 1000 first.
  • Prefer time_t or uint64_t for the input; ULONG can overflow on 32-bit builds and will hit the Year 2038 limit.
  • Use the thread-safe variants shown (gmtime_r/localtime_r on POSIX, gmtime_s/localtime_s on Windows).
  • If you only need UTC, always use gmtime*; localtime* will apply your system timezone and DST rules.

Recommended Answers

All 9 Replies

Member Avatar for ArkM

Can you explain what is meant by "unix timestamp" and (mainly) "system timestamp"?

Member Avatar for spanigrahi_situ

Can you explain what is meant by "unix timestamp" and (mainly) "system timestamp"?

unix time stamp is like = 1227806311
the same system time stamp is = 27/11/2008 HR MIN SEC

Member Avatar for ArkM

I have never seen before so funny "definitions" of a "unix timestamp" data type and a "system time" representation: ;)

unix time stamp is like = 1227806311
the same system time stamp is = 27/11/2008 HR MIN SEC

Well, try to adopt this code:

/* UnixTime is unspecified unix time stamp type.
     * Define it before compilation, for example:
     * typedef time_t UnixTime;
     *  or
     * typedef long int UnixTime;
     */
    UnixTime ut;  /* Unix timestamp to be converted */

    time_t thist; /* This system timestamp value */
    struct tm* ptm;
    char mysyst[20] = "\?"; /* for "sys time" */
    const char* fmt = "%d/%m/%Y %H %M %S"; /* sys?time */
    /* C Standard does not specify what's time_t epoch */
    time_t uepoch; /* Unix epoch in this system time_t */
    struct tm tmepoch;
    /* Prepare unix time epoch on this system */
    memset(&tmepoch,0,sizeof tmepoch);
    tmepoch.tm_year = 1970 - 1900;
    tmepoch.tm_mon = 1 - 1;
    tmepoch.tm_mday = 1;
    tmepoch.tm_hour = 0;
    tmepoch.tm_min = 0;
    tmepoch.tm_sec = 0;
    uepoch = mktime(&tmepoch); /* this system unix epoch */
    /* Recalculate unix time to this system time_t */
    thist = (time_t)ut - uepoch;
    ptm = gmtime(&thist); 
    if (ptm && strftime(mysyst,sizeof mysyst,fmt,ptm))
        printf("%s\n",mysyst);
Member Avatar for spanigrahi_situ

Sry to tell you guys my output time should be GMT or UTC.Any one plz help me on this urgently?

Member Avatar for spanigrahi_situ

hmmmm dude i was busy with some other issues.

Member Avatar for ArkM

hmmmm dude i was busy with some other issues.

Just the TIME to go on with that issues ;)...

Member Avatar for Salem

> hmmmm dude i was busy with some other issues.
Your choice - give up programming or give up something else.

You're not going to learn anything by dipping into programming for a couple of hours a month, so I'd say give up.

Otherwise you would have found a way to do something in the last fortnight, rather than just showing up here at the last minute hoping for salvation.

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