Time#strftime

static VALUE
time_strftime(VALUE time, VALUE format)
{
    struct time_object *tobj;
    const char *fmt;
    rb_len_t len;
    rb_encoding *enc;
    VALUE tmp;

    GetTimeval(time, tobj);
    MAKE_TM_ENSURE(time, tobj, tobj->vtm.yday != 0);
    StringValue(format);
    if (!rb_enc_str_asciicompat_p(format)) {
        rb_raise(rb_eArgError, "format should have ASCII compatible encoding");
    }
    tmp = rb_str_tmp_frozen_acquire(format);
    fmt = RSTRING_PTR(tmp);
    len = RSTRING_LEN(tmp);
    enc = rb_enc_get(format);
    if (len == 0) {
        rb_warning("strftime called with empty format string");
        return rb_enc_str_new(0, 0, enc);
    }
    else {
        VALUE str = rb_strftime_alloc(fmt, len, enc, time, &tobj->vtm, tobj->timew,
                                      TZMODE_UTC_P(tobj));
        rb_str_tmp_frozen_release(format, tmp);
        if (!str) rb_raise(rb_eArgError, "invalid format: %"PRIsVALUE, format);
        return str;
    }
}