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Software Vault: The Gold Collection
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Software Vault - The Gold Collection (American Databankers) (1993).ISO
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cuj9303.zip
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1103098A
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1993-06-21
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74 lines
// date6.cpp
#include <assert.h>
#include "date6.h"
inline int isleap(int y)
{return y%4 == 0 && y%100 != 0 || y%400 == 0;}
static int dtab[2][13] =
{
{0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
{0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
};
Date Date::operator-(const Date& d2) const
{
int months, days, years, prev_month, order;
const Date * first, * last;
// Must know which date is first
if (compare(d2) <= 0)
{
// this <= d2
order = -1;
first = this;
last = &d2;
}
else
{
order = 1;
first = &d2;
last = this;
}
// Compute the interval; first <= last
years = last->year - first->year;
months = last->month - first->month;
days = last->day - first->day;
assert(years >= 0 && months >= 0 && days >= 0);
// Do obvious corrections (days before months!)
//
// This is a loop in case the previous month is
// February, and days < -28.
prev_month = last->month - 1;
while (days < 0)
{
// Borrow from the previous month
if (prev_month == 0)
prev_month = 12;
--months;
days += dtab[isleap(last->year)][prev_month--];
}
if (months < 0)
{
// Borrow from the previous year
--years;
months += 12;
}
// Return a date object with the interval
if (order == -1)
return Date(-months,-days,-years);
else
return Date(months,days,years);
}
int Date::compare(const Date& d2) const
{
// same as in Listing 2
}