Formatting struct timespec

Question

How to format struct timespec to string? This structure is returned e.g. by clock_gettime() on Linux gcc:

struct timespec {
    tim         


        

Answer 1

I wanted to ask the same question. Here is my current solution to obtain a string like this: 2013-02-07 09:24:40.749355372 I am not sure if there is a more straight forward solution than this, but at least the string format is freely configurable with this approach.

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

#define NANO 1000000000L

// buf needs to store 30 characters
int timespec2str(char *buf, uint len, struct timespec *ts) {
    int ret;
    struct tm t;

    tzset();
    if (localtime_r(&(ts->tv_sec), &t) == NULL)
        return 1;

    ret = strftime(buf, len, "%F %T", &t);
    if (ret == 0)
        return 2;
    len -= ret - 1;

    ret = snprintf(&buf[strlen(buf)], len, ".%09ld", ts->tv_nsec);
    if (ret >= len)
        return 3;

    return 0;
}

int main(int argc, char **argv) {
    clockid_t clk_id = CLOCK_REALTIME;
    const uint TIME_FMT = strlen("2012-12-31 12:59:59.123456789") + 1;
    char timestr[TIME_FMT];

    struct timespec ts, res;
    clock_getres(clk_id, &res);
    clock_gettime(clk_id, &ts);

    if (timespec2str(timestr, sizeof(timestr), &ts) != 0) {
        printf("timespec2str failed!\n");
        return EXIT_FAILURE;
    } else {
        unsigned long resol = res.tv_sec * NANO + res.tv_nsec;
        printf("CLOCK_REALTIME: res=%ld ns, time=%s\n", resol, timestr);
        return EXIT_SUCCESS;
    }
}

output:

gcc mwe.c -lrt 
$ ./a.out 
CLOCK_REALTIME: res=1 ns, time=2013-02-07 13:41:17.994326501

Answer 2

One way to format it is:

printf("%lld.%.9ld", (long long)ts.tv_sec, ts.tv_nsec);

Answer 3

You can pass the tv_sec parameter to some of the formatting function. Have a look at gmtime, localtime(). Then look at snprintf.

Answer 4

You could use a std::stringstream. You can stream anything into it:

std::stringstream stream;
stream << 5.7;
stream << foo.bar;

std::string s = stream.str();

That should be a quite general approach. (Works only for C++, but you asked the question for this language too.)