date - How to determine which day is the first in week in current locale in C

Question

How to determine which day is the first in week in current locale in C. In Russia monday is the first day, but my mac shows localized calendar with wrong first day. So i wonder if i can determine which day is the first in current locale. Thanks.

anatoly@mb:/Users/anatoly$ cal
     Июля 2012
вс пн вт ср чт пт сб
 1  2  3  4  5  6  7
 8  9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31

Answer 1

With glibc, you can do:

#define _GNU_SOURCE
#include <langinfo.h>

char get_first_weekday()
{
    return *nl_langinfo(_NL_TIME_FIRST_WEEKDAY);
}

Remember to call setlocale() first. Example:

#include <stdio.h>
#include <locale.h>

int main()
{
    setlocale(LC_ALL, "");
    printf("%d
", get_first_weekday());
    return 0;
}

This returns 2 on my system (which means monday == DAY_2).

Just a note: I don't think it's public API of glibc. However, this is how locale tool bundled with it gets first weekday. cal uses similar method as well.

Depending on a particular use, you may be interested in _NL_TIME_FIRST_WORKDAY as well.