Struct timeval to printable format

Question

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

Answer 1

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

Answer 2

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

Answer 3

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.%06d", 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").