datetime.cpp

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    if ( *month == wxDateTime::Inv_Month )
    {
        if ( !tmNow )
            tmNow = wxDateTime::GetTmNow();

        *month = (wxDateTime::Month)tmNow->tm_mon;
    }
}

// fll the struct tm with default values
static void InitTm(struct tm& tm)
{
    // struct tm may have etxra fields (undocumented and with unportable
    // names) which, nevertheless, must be set to 0
    memset(&tm, 0, sizeof(struct tm));

    tm.tm_mday = 1;   // mday 0 is invalid
    tm.tm_year = 76;  // any valid year
    tm.tm_isdst = -1; // auto determine
}

// parsing helpers
// ---------------

// return the month if the string is a month name or Inv_Month otherwise
static wxDateTime::Month GetMonthFromName(const wxString& name, int flags)
{
    wxDateTime::Month mon;
    for ( mon = wxDateTime::Jan; mon < wxDateTime::Inv_Month; wxNextMonth(mon) )
    {
        // case-insensitive comparison either one of or with both abbreviated
        // and not versions
        if ( flags & wxDateTime::Name_Full )
        {
            if ( name.CmpNoCase(wxDateTime::
                        GetMonthName(mon, wxDateTime::Name_Full)) == 0 )
            {
                break;
            }
        }

        if ( flags & wxDateTime::Name_Abbr )
        {
            if ( name.CmpNoCase(wxDateTime::
                        GetMonthName(mon, wxDateTime::Name_Abbr)) == 0 )
            {
                break;
            }
        }
    }

    return mon;
}

// return the weekday if the string is a weekday name or Inv_WeekDay otherwise
static wxDateTime::WeekDay GetWeekDayFromName(const wxString& name, int flags)
{
    wxDateTime::WeekDay wd;
    for ( wd = wxDateTime::Sun; wd < wxDateTime::Inv_WeekDay; wxNextWDay(wd) )
    {
        // case-insensitive comparison either one of or with both abbreviated
        // and not versions
        if ( flags & wxDateTime::Name_Full )
        {
            if ( name.CmpNoCase(wxDateTime::
                        GetWeekDayName(wd, wxDateTime::Name_Full)) == 0 )
            {
                break;
            }
        }

        if ( flags & wxDateTime::Name_Abbr )
        {
            if ( name.CmpNoCase(wxDateTime::
                        GetWeekDayName(wd, wxDateTime::Name_Abbr)) == 0 )
            {
                break;
            }
        }
    }

    return wd;
}

// scans all digits (but no more than len) and returns the resulting number
static bool GetNumericToken(size_t len, const wxChar*& p, unsigned long *number)
{
    size_t n = 1;
    wxString s;
    while ( wxIsdigit(*p) )
    {
        s += *p++;

        if ( len && ++n > len )
            break;
    }

    return !s.empty() && s.ToULong(number);
}

// scans all alphabetic characters and returns the resulting string
static wxString GetAlphaToken(const wxChar*& p)
{
    wxString s;
    while ( wxIsalpha(*p) )
    {
        s += *p++;
    }

    return s;
}

// ============================================================================
// implementation of wxDateTime
// ============================================================================

// ----------------------------------------------------------------------------
// struct Tm
// ----------------------------------------------------------------------------

wxDateTime::Tm::Tm()
{
    year = (wxDateTime_t)wxDateTime::Inv_Year;
    mon = wxDateTime::Inv_Month;
    mday = 0;
    hour = min = sec = msec = 0;
    wday = wxDateTime::Inv_WeekDay;
}

wxDateTime::Tm::Tm(const struct tm& tm, const TimeZone& tz)
              : m_tz(tz)
{
    msec = 0;
    sec = (wxDateTime::wxDateTime_t)tm.tm_sec;
    min = (wxDateTime::wxDateTime_t)tm.tm_min;
    hour = (wxDateTime::wxDateTime_t)tm.tm_hour;
    mday = (wxDateTime::wxDateTime_t)tm.tm_mday;
    mon = (wxDateTime::Month)tm.tm_mon;
    year = 1900 + tm.tm_year;
    wday = (wxDateTime::wxDateTime_t)tm.tm_wday;
    yday = (wxDateTime::wxDateTime_t)tm.tm_yday;
}

bool wxDateTime::Tm::IsValid() const
{
    // we allow for the leap seconds, although we don't use them (yet)
    return (year != wxDateTime::Inv_Year) && (mon != wxDateTime::Inv_Month) &&
           (mday <= GetNumOfDaysInMonth(year, mon)) &&
           (hour < 24) && (min < 60) && (sec < 62) && (msec < 1000);
}

void wxDateTime::Tm::ComputeWeekDay()
{
    // compute the week day from day/month/year: we use the dumbest algorithm
    // possible: just compute our JDN and then use the (simple to derive)
    // formula: weekday = (JDN + 1.5) % 7
    wday = (wxDateTime::wxDateTime_t)((wxDateTime::WeekDay)(GetTruncatedJDN(mday, mon, year) + 2) % 7);
}

void wxDateTime::Tm::AddMonths(int monDiff)
{
    // normalize the months field
    while ( monDiff < -mon )
    {
        year--;

        monDiff += MONTHS_IN_YEAR;
    }

    while ( monDiff + mon >= MONTHS_IN_YEAR )
    {
        year++;

        monDiff -= MONTHS_IN_YEAR;
    }

    mon = (wxDateTime::Month)(mon + monDiff);

    wxASSERT_MSG( mon >= 0 && mon < MONTHS_IN_YEAR, _T("logic error") );

    // NB: we don't check here that the resulting date is valid, this function
    //     is private and the caller must check it if needed
}

void wxDateTime::Tm::AddDays(int dayDiff)
{
    // normalize the days field
    while ( dayDiff + mday < 1 )
    {
        AddMonths(-1);

        dayDiff += GetNumOfDaysInMonth(year, mon);
    }

    mday = (wxDateTime::wxDateTime_t)( mday + dayDiff );
    while ( mday > GetNumOfDaysInMonth(year, mon) )
    {
        mday -= GetNumOfDaysInMonth(year, mon);

        AddMonths(1);
    }

    wxASSERT_MSG( mday > 0 && mday <= GetNumOfDaysInMonth(year, mon),
                  _T("logic error") );
}

// ----------------------------------------------------------------------------
// class TimeZone
// ----------------------------------------------------------------------------

wxDateTime::TimeZone::TimeZone(wxDateTime::TZ tz)
{
    switch ( tz )
    {
        case wxDateTime::Local:
            // get the offset from C RTL: it returns the difference GMT-local
            // while we want to have the offset _from_ GMT, hence the '-'
            m_offset = -GetTimeZone();
            break;

        case wxDateTime::GMT_12:
        case wxDateTime::GMT_11:
        case wxDateTime::GMT_10:
        case wxDateTime::GMT_9:
        case wxDateTime::GMT_8:
        case wxDateTime::GMT_7:
        case wxDateTime::GMT_6:
        case wxDateTime::GMT_5:
        case wxDateTime::GMT_4:
        case wxDateTime::GMT_3:
        case wxDateTime::GMT_2:
        case wxDateTime::GMT_1:
            m_offset = -3600*(wxDateTime::GMT0 - tz);
            break;

        case wxDateTime::GMT0:
        case wxDateTime::GMT1:
        case wxDateTime::GMT2:
        case wxDateTime::GMT3:
        case wxDateTime::GMT4:
        case wxDateTime::GMT5:
        case wxDateTime::GMT6:
        case wxDateTime::GMT7:
        case wxDateTime::GMT8:
        case wxDateTime::GMT9:
        case wxDateTime::GMT10:
        case wxDateTime::GMT11:
        case wxDateTime::GMT12:
            m_offset = 3600*(tz - wxDateTime::GMT0);
            break;

        case wxDateTime::A_CST:
            // Central Standard Time in use in Australia = UTC + 9.5
            m_offset = 60l*(9*MIN_PER_HOUR + MIN_PER_HOUR/2);
            break;

        default:
            wxFAIL_MSG( _T("unknown time zone") );
    }
}

// ----------------------------------------------------------------------------
// static functions
// ----------------------------------------------------------------------------

/* static */
bool wxDateTime::IsLeapYear(int year, wxDateTime::Calendar cal)
{
    if ( year == Inv_Year )
        year = GetCurrentYear();

    if ( cal == Gregorian )
    {
        // in Gregorian calendar leap years are those divisible by 4 except
        // those divisible by 100 unless they're also divisible by 400
        // (in some countries, like Russia and Greece, additional corrections
        // exist, but they won't manifest themselves until 2700)
        return (year % 4 == 0) && ((year % 100 != 0) || (year % 400 == 0));
    }
    else if ( cal == Julian )
    {
        // in Julian calendar the rule is simpler
        return year % 4 == 0;
    }
    else
    {
        wxFAIL_MSG(_T("unknown calendar"));

        return false;
    }
}

/* static */
int wxDateTime::GetCentury(int year)
{
    return year > 0 ? year / 100 : year / 100 - 1;
}

/* static */
int wxDateTime::ConvertYearToBC(int year)
{
    // year 0 is BC 1
    return year > 0 ? year : year - 1;
}

/* static */
int wxDateTime::GetCurrentYear(wxDateTime::Calendar cal)
{
    switch ( cal )
    {
        case Gregorian:
            return Now().GetYear();

        case Julian:
            wxFAIL_MSG(_T("TODO"));
            break;

        default:
            wxFAIL_MSG(_T("unsupported calendar"));
            break;
    }

    return Inv_Year;
}

/* static */
wxDateTime::Month wxDateTime::GetCurrentMonth(wxDateTime::Calendar cal)
{
    switch ( cal )
    {
        case Gregorian:
            return Now().GetMonth();

        case Julian:
            wxFAIL_MSG(_T("TODO"));
            break;

        default:
            wxFAIL_MSG(_T("unsupported calendar"));
            break;
    }

    return Inv_Month;
}

/* static */
wxDateTime::wxDateTime_t wxDateTime::GetNumberOfDays(int year, Calendar cal)
{
    if ( year == Inv_Year )
    {
        // take the current year if none given
        year = GetCurrentYear();
    }

    switch ( cal )
    {
        case Gregorian:
        case Julian:
            return IsLeapYear(year) ? 366 : 365;

        default:
            wxFAIL_MSG(_T("unsupported calendar"));
            break;
    }

    return 0;
}

/* static */
wxDateTime::wxDateTime_t wxDateTime::GetNumberOfDays(wxDateTime::Month month,
                                                     int year,
                                                     wxDateTime::Calendar cal)
{
    wxCHECK_MSG( month < MONTHS_IN_YEAR, 0, _T("invalid month") );

    if ( cal == Gregorian || cal == Julian )
    {
        if ( year == Inv_Year )
        {
            // take the current year if none given
            year = GetCurrentYear();
        }

        return GetNumOfDaysInMonth(year, month);
    }
    else
    {
        wxFAIL_MSG(_T("unsupported calendar"));

        return 0;
    }
}

/* static */
wxString wxDateTime::GetMonthName(wxDateTime::Month month,
                                  wxDateTime::NameFlags flags)
{
    wxCHECK_MSG( month != Inv_Month, wxEmptyString, _T("invalid month") );
#ifndef __WXWINCE__
    // notice that we must set all the fields to avoid confusing libc (GNU one
    // gets confused to a crash if we don't do this)
    tm tm;
    InitTm(tm);
    tm.tm_mon = month;

    return CallStrftime(flags == Name_Abbr ? _T("%b") : _T("%B"), &tm);
#else
    wxString ret;
    switch(month)
    {
        case Jan:
            ret = (flags == Name_Abbr ? wxT("Jan"): wxT("January"));
            break;
        case Feb:
            ret = (flags == Name_Abbr ? wxT("Feb"): wxT("Febuary"));
            break;
        case Mar:
            ret = (flags == Name_Abbr ? wxT("Mar"): wxT("March"));
            break;
        case Apr:
            ret = (flags == Name_Abbr ? wxT("Apr"): wxT("April"));
            break;
        case May:
            ret = (flags == Name_Abbr ? wxT("May"): wxT("May"));
            break;
        case Jun:
            ret = (flags == Name_Abbr ? wxT("Jun"): wxT("June"));
            break;
        case Jul:
            ret = (flags == Name_Abbr ? wxT("Jul"): wxT("July"));
            break;
        case Aug:
            ret = (flags == Name_Abbr ? wxT("Aug"): wxT("August"));
            break;
        case Sep:
            ret = (flags == Name_Abbr ? wxT("Sep"): wxT("September"));
            break;
        case Oct:
            ret = (flags == Name_Abbr ? wxT("Oct"): wxT("October"));
            break;
        case Nov: