Struct timeval to printable format

问题:

Could you please help me how to format a struct timeval instance to human readable format like "2010-01-01 15:35:10.0001"?

回答1:

Convert the tv_sec using localtime, and strftime, then append tv_usec part.

回答2:

You need to manually append the microseconds part, since it's not in the struct tm that strftime() deals with. Here's a snippet:

struct timeval tv; time_t nowtime; struct tm *nowtm; char tmbuf[64], buf[64];  gettimeofday(&tv, NULL); nowtime = tv.tv_sec; nowtm = localtime(&nowtime); strftime(tmbuf, sizeof tmbuf, "%Y-%m-%d %H:%M:%S", nowtm); snprintf(buf, sizeof buf, "%s.%06ld", tmbuf, tv.tv_usec); 

Note how we use explicit precision of 06 to get a zero-filled microseconds field. Since the microseconds go from 0 to 999,999, it must always be padded to 6 digits. We don't want to misrepresent e.g. 57 microseconds as 570,000 (compare "1.57" vs "1.000057").

回答3:

ctime((const time_t *) &timeval.ts.tv_sec) 

I think you are looking for this code, just for your reference.

回答4:

You can use the strftime function to convert a date and time to a string.

回答5:

Combining previous answers and comments, changing the format to be RFC3339-compliant, and checking all of the error conditions, you get this:

#include  #include   ssize_t format_timeval(struct timeval *tv, char *buf, size_t sz) {   ssize_t written = -1;   struct tm *gm = gmtime(&tv->tv_sec);    if (gm)   {     written = (ssize_t)strftime(buf, sz, "%Y-%m-%dT%H:%M:%S", gm);     if ((written > 0) && ((size_t)written tv_usec);       written = (w > 0) ? written + w : -1;     }   }   return written; }  int main() {   struct timeval tv;   char buf[28];   if (gettimeofday(&tv, NULL) != 0) {     perror("gettimeofday");     return 1;   }   if (format_timeval(&tv, buf, sizeof(buf)) > 0) {     printf("%s\n", buf);     // sample output:     // 2015-05-09T04:18:42.514551Z   }   return 0; } 

回答6:

Convert the tv_sec using localtime_s instead of localtime, because if you are writing a global function it may cause some problems. if your function may work in a multi-threaded solution then please consider using localtime_r

回答7:

This is what I use:

#include  #include   #ifdef _WIN32 #define WIN32_LEAN_AND_MEAN #include  #include  #define gmtime_r(ptime,ptm) (gmtime_s((ptm),(ptime)), (ptm)) #else #include  #endif  #define ISO8601_LEN (sizeof "1970-01-01T23:59:59.123456Z")  char *timeval_to_str(char iso8601[restrict static ISO8601_LEN], unsigned precision, const struct timeval * restrict tv) {     struct tm tm;     if (!gmtime_r(&tv->tv_sec, &tm))         return memcpy(iso8601, "Error: Year overflow", sizeof "Error: Year overflow");      tm.tm_year %= 10*1000;     char *frac = iso8601 + strftime(iso8601, sizeof "1970-01-01T23:59:59.", "%Y-%m-%dT%H:%M:%SZ", &tm);      if (precision) {         unsigned long usecs = tv->tv_usec;         for (int i = precision; i  frac) while (*spaces == ' ') *spaces-- = '0';     }      return iso8601; } 

precision specifies the width of the seconds fraction. Code is y10k- and yINT_MAX-proof.

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