GDATE.C

/******************************************************************************\ 
*       This is a part of the Microsoft Source Code Samples.  
*       Copyright 1993 - 1998 Microsoft Corporation. 
*       All rights reserved.  
*       This source code is only intended as a supplement to  
*       Microsoft Development Tools and/or WinHelp documentation. 
*       See these sources for detailed information regarding the  
*       Microsoft samples programs. 
\******************************************************************************/ 
 
/****************************** Module Header ******************************* 
* Module Name: GDATE.C 
* 
* Contains date conversion functions. 
* 
* Functions: 
* 
* gdi_isleap() 
* gdate_daytodmy() 
* gdate_dmytoday() 
* gdate_monthdays() 
* gdate_weeklyday() 
* 
* Comments: 
* 
****************************************************************************/ 
 
#include <windows.h> 
#include <string.h> 
 
#include "gutils.h" 
 
 
BOOL gdi_isleap(LONG year); 
 
/*---static data--------------------------------------------*/ 
 
int monthdays[] = { 
        31, 
        28, 
        31, 
        30, 
        31, 
        30, 
        31, 
        31, 
        30, 
        31, 
        30, 
        31 
}; 
 
 
/*************************************************************************** 
 * Function: gdate_daytomy 
 * 
 * Purpose: 
 * 
 * converts day to d/m/y 
 */ 
void APIENTRY 
gdate_daytodmy(LONG days, int FAR* yrp, int FAR* monthp, int FAR* dayp) 
{ 
        int years; 
        int nleaps; 
        int month; 
        int mdays; 
 
        /* get number of completed years and calc leap days */ 
        years = (int) (days / 365); 
        days = days % 365; 
        nleaps = (years / 4) - (years / 100) + (years / 400); 
        while (nleaps > days) { 
                days += 365; 
                years--; 
                nleaps = (years / 4) - (years / 100) + (years / 400); 
        } 
        days -= nleaps; 
 
        /* add one year for current (non-complete) year */ 
        years++; 
 
 
        /* current month */ 
        for (month = 0; month < 12; month++) { 
                mdays = monthdays[month]; 
                if (gdi_isleap(years) && (month == 1)) { 
                        mdays++; 
                } 
                if (days == mdays) { 
                        days = 0; 
                        month++; 
                        break; 
                } else if (days < mdays) { 
                        break; 
                } else { 
                        days -= mdays; 
                } 
        } 
        /* conv month from 0-11 to 1-12 */ 
        if (monthp != NULL) { 
                *monthp = month+1; 
        } 
        if (dayp != NULL) { 
                *dayp = (int) days + 1; 
        } 
        if (yrp != NULL) { 
                *yrp = years; 
        } 
} 
 
 
/*************************************************************************** 
 * Function: gdate_dmytoday 
 * 
 * Purpose: 
 * 
 * converts d/m/y to a day 
 */  
LONG APIENTRY 
gdate_dmytoday(int yr, int month, int day) 
{ 
        int nleaps; 
        int i; 
        long ndays; 
 
        /* exclude the current year */ 
        yr--; 
        nleaps = (yr / 4) - (yr / 100) + (yr / 400); 
 
        /* in any given year, day 0 is jan1 */ 
        month--; 
        day--; 
        ndays = 0; 
        for (i = 0; i < month ; i++) { 
                ndays += monthdays[i]; 
                if (gdi_isleap(yr+1) && (i == 1)) { 
                        ndays++; 
                } 
        } 
        ndays = ndays + day + nleaps + (yr * 365L); 
        return(ndays); 
} 
 
/*************************************************************************** 
 * Function: gdate_monthdays 
 * 
 * Purpose: 
 * 
 * Gets number of days in month 
 */ 
int APIENTRY 
gdate_monthdays(int month, int year) 
{ 
        int ndays; 
 
        ndays = monthdays[month - 1]; 
        if (gdi_isleap(year) && (month == 2)) { 
                ndays++; 
        } 
        return(ndays); 
} 
 
/*************************************************************************** 
 * Function: gdate_weekday 
 * 
 * Purpose: 
 *  
 * Gets the day of the week 
 */ 
int APIENTRY 
gdate_weekday(long daynr) 
{ 
        return((int) ((daynr + 1) % 7)); 
} 
 
 
/*************************************************************************** 
 * Function: gdi_isleap 
 * 
 * Purpose: 
 *  
 * Determines whether the year is a leap year 
 */ 
BOOL 
gdi_isleap(LONG year) 
{ 
        if ( ((year % 4) == 0) && 
                (((year % 100) != 0) || 
                ((year % 400) == 0))) { 
                        return TRUE; 
        } else { 
                return FALSE; 
        } 
}