Convert string time to unix time and vice versa

Question

I tried to just convert the string "1998-04-11" to a UNIX timestamp, which should be 892245600 according to the online converter.

But I still get a different result.

struct tm tm; time_t ts; strptime("1998-04-11", "%Y-%m-%d", &tm); tm.tm_mon = tm.tm_mon -1; ts = mktime(&tm); printf("%d \n", (int)ts); //unix time-stamp printf("%s \n", ctime(&ts)); //human readable date 

Result:

 893502901 Sat Apr 25 13:15:01 1998 

Can someone tell me what I am doing wrong?

Answer 1

End tm structure before strptime call

 memset(&tm, 0, sizeof(struct tm)); 

In the notes section: http://man7.org/linux/man-pages/man3/strptime.3.html

In principle, this function does not initialize tm , but only stores the specified values. This means that tm must be initialized before the call.

And memset used, as indicated above, in the example from the same page.

Answer 2

This is an uninitialized memory issue.

 (gdb) p tm $1 = {tm_sec = 1, tm_min = 0, tm_hour = 4196061, tm_mday = 0, tm_mon = -5984, tm_year = 32767, tm_wday = 0, tm_yday = 0, tm_isdst = 4195984, tm_gmtoff = 4195616, tm_zone = 0x7fffffffe980 "\001"} 

As you can see in the debugger, struct tm has arbitrary memory. Create garbage offset time_zone.

After strptime is executed:

 (gdb) p tm $3 = {tm_sec = 1, tm_min = 0, tm_hour = 4196061, tm_mday = 11, tm_mon = 3, tm_year = 98, tm_wday = 6, tm_yday = 100, tm_isdst = 4195984, tm_gmtoff = 4195616, tm_zone = 0x7fffffffe980 "\001"} 

Besides:

 tm.tm_mon = tm.tm_mon -1; 

Not necessary. Corrected Code:

 #include <time.h> #include <stdio.h> #include <string.h> int main(int argc, char **argv) { struct tm tm; time_t ts = 0; memset(&tm, 0, sizeof(tm)); strptime("1998-04-11", "%Y-%m-%d", &tm); ts = mktime(&tm); printf("%d \n", (int)ts); //unix time-stamp printf("%s \n", ctime(&ts)); //human readable date } 

Output:

 892252800 Sat Apr 11 00:00:00 1998