source: azure_iot_hub/trunk/musl-1.1.18/src/time/wcsftime.c@ 388

#include <wchar.h>
#include <time.h>
#include <locale.h>
#include "locale_impl.h"
#include "libc.h"

const char *__strftime_fmt_1(char (*s)[100], size_t *l, int f, const struct tm *tm, locale_t loc);

size_t __wcsftime_l(wchar_t *restrict s, size_t n, const wchar_t *restrict f, const struct tm *restrict tm, locale_t loc)
{
        size_t l, k;
        char buf[100];
        wchar_t wbuf[100];
        wchar_t *p;
        const char *t_mb;
        const wchar_t *t;
        int plus;
        unsigned long width;
        for (l=0; l<n; f++) {
                if (!*f) {
                        s[l] = 0;
                        return l;
                }
                if (*f != '%') {
                        s[l++] = *f;
                        continue;
                }
                f++;
                if ((plus = (*f == '+'))) f++;
                width = wcstoul(f, &p, 10);
                if (*p == 'C' || *p == 'F' || *p == 'G' || *p == 'Y') {
                        if (!width && p!=f) width = 1;
                } else {
                        width = 0;
                }
                f = p;
                if (*f == 'E' || *f == 'O') f++;
                t_mb = __strftime_fmt_1(&buf, &k, *f, tm, loc);
                if (!t_mb) break;
                k = mbstowcs(wbuf, t_mb, sizeof wbuf / sizeof *wbuf);
                if (k == (size_t)-1) return 0;
                t = wbuf;
                if (width) {
                        for (; *t=='+' || *t=='-' || (*t=='0'&&t[1]); t++, k--);
                        width--;
                        if (plus && tm->tm_year >= 10000-1900)
                                s[l++] = '+';
                        else if (tm->tm_year < -1900)
                                s[l++] = '-';
                        else
                                width++;
                        for (; width > k && l < n; width--)
                                s[l++] = '0';
                }
                if (k >= n-l) k = n-l;
                wmemcpy(s+l, t, k);
                l += k;
        }
        if (n) {
                if (l==n) l=n-1;
                s[l] = 0;
        }
        return 0;
}

size_t wcsftime(wchar_t *restrict wcs, size_t n, const wchar_t *restrict f, const struct tm *restrict tm)
{
        return __wcsftime_l(wcs, n, f, tm, CURRENT_LOCALE);
}

weak_alias(__wcsftime_l, wcsftime_l);