gdatetimetest.c

/**
 * Build using:
 *   gcc -o datetest gdatetimetest.c $(pkg-config --cflags --libs glib-2.0)
 */

#include <glib.h>
#include <locale.h>

int main(int argc, char *argv[])
{
    /* set LC_ALL to nothing, so that the remaining locale settings
     * (LC_TIME, LANG..)  are used */
    setlocale(LC_ALL, "");

    GTimeZone *tz = g_time_zone_new("Europe/Warsaw");
    g_assert_nonnull(tz);
    GDateTime *dt = g_date_time_new_now_utc();
    g_assert_nonnull(dt);

    GDateTime *zdt = g_date_time_to_timezone(dt, tz);
    g_assert_nonnull(zdt);

    const gchar *format_good = "%a %d %b %Y - %H:%M";
    /* utf-8 encoded by the editor */
    const gchar *format_bad = "łłóó %a %d %b %Y - %H:%M";
    g_assert(g_utf8_validate(format_bad, -1, NULL) == TRUE);

    const char *charset;
    gboolean is_utf8 = g_get_charset(&charset);
    g_message("is utf-8? %s charset %s",
              (is_utf8 == TRUE) ? "yes" : "no",
              charset);
    if (is_utf8 != TRUE)
    {
        /* Replicate what g_date_time_format_locale() does. Input
         * format is assumed to be utf-8 encoded, thus when locale is
         * not utf-8 a conversion utf-8 -> locale is needed. */
        GError *err = NULL;
        g_message("non UTF-8 locale, try conversion");
        gchar *tmp;
        tmp = g_locale_from_utf8 (format_bad, -1, NULL, NULL, &err);
        if (!tmp)
        {
            g_message("conversion failed: %s", err->message);
            g_error_free(err);
        }
        else
        {
            g_free(tmp);
        }

    }

    gchar *as_string_good = g_date_time_format(zdt, format_good);
    gchar *as_string_bad = g_date_time_format(zdt, format_bad);

    g_printf("as string good: %s\n", as_string_good);
    g_printf("as string bad: %s\n", as_string_bad);

    g_free(as_string_bad);
    g_free(as_string_good);
    g_date_time_unref(zdt);
    g_date_time_unref(dt);
    g_time_zone_unref(tz);

    return 0;
}