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:
https://i.stack.imgur.com/F8Qlx.jpg

@@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;
}