C, time, day of month, year and more - c

Question

I've got a problem.
I need to get things like day of year, day of month, month of year etc.
I use this code:
#include <stdio.h>
#include <time.h>
int main(void)
{
time_t liczba_sekund;
struct tm strukt;
time(&liczba_sekund);
localtime_r(&liczba_sekund, &strukt);
printf("today is %d day of year\nmonth is %d, month's day %d\n", strukt.tm_yday+1, strukt.tm_mon+1, strukt.tm_mday);
return 0;
}
First thing: why does gcc -std=c99 -pedantic -Wall return this warning:
My input: gcc test_data.c -o test_data.out -std=c99 -pedantic -Wall
Output:
test_data.c: In function ‘main’:
test_data.c:11:3: warning: implicit declaration of function ‘localtime_r’ [-Wimplicit-function-declaration]
Second thing: how to make it work on windows? While trying to compile it using Dev-C, I got this:
http://imgur.com/U7dyE
##EDIT --------------------
I have found an example for your localtime suggestion:
#include <stdio.h>
#include <time.h>
int main ()
{
time_t time_raw_format;
struct tm * ptr_time;
time ( &time_raw_format );
ptr_time = localtime ( &time_raw_format );
printf ("Current local time and date: %s", asctime(ptr_time));
return 0;
}
How can I change this to date format like this: 5.12.2012 or 5-12-2012? And how to get the day of the year?
I would love if the solution worked both on windows and linux.

Answer 1

localtime_r is not part of the C standard. Maybe you were looking for localtime?
localtime_r is really available on many linux systems:
Thread-safe versions asctime_r(), ctime_r(), gmtime_r() and localtime_r() are specified by SUSv2, and available since libc 5.2.5
However, since it isn't part of the standard you cannot use it on Windows.
How can I change this to date format like this: 5.12.2012 or 5-12-2012? And how to get the day of the year?
You have to use strftime instead of asctime:
int main ()
{
time_t time_raw_format;
struct tm * ptr_time;
char buffer[50];
time ( &time_raw_format );
ptr_time = localtime ( &time_raw_format );
if(strftime(buffer,50,"%d.%m.%Y",ptr_time) == 0){
perror("Couldn't prepare formatted string");
} else {
printf ("Current local time and date: %s", buffer);
}
return 0;
}

Answer 2

localtime on Windows should be thread-safe per: http://msdn.microsoft.com/en-us/library/bf12f0hc%28VS.80%29.aspx
Both the 32-bit and 64-bit versions ofgmtime, mktime, mkgmtime, and
localtimeall use a single tm structure per thread for the conversion.
Each call to one of these routines destroys the result of the previous
call.