两个日期之间的月差
如何计算C＃中两个日期之间的差异？
在C＃中是否有相当于VB的DateDiff()方法。 我需要在两个相隔几年的日期之间找到几个月的差异。 该文件说，我可以使用TimeSpan ：
TimeSpan ts = date1 - date2;
但是这给了我几天的数据。 我不想把这个数字除以30，因为不是每个月都是30天，而且因为两个操作数值彼此很不相同，所以我除以30会给我一个错误的值。
有什么建议么？
假设月份的日期不相关（即2011.1.1与2010.12.31之间的差异为1），并且date1> date2给出正值，date2> date1则为负值
((date1.Year - date2.Year) * 12) + date1.Month - date2.Month
或者，假设您希望两个日期之间的“平均月份数”大致相同，以下情况应适用于所有日期差异，但日期差异很大。
date1.Subtract(date2).Days / (365.25 / 12)
请注意，如果您要使用后一种解决方案，那么您的单元测试应该说明您的应用程序设计的最宽日期范围，并相应地验证计算结果。
更新（感谢加里）
如果使用“平均月份”方法，则用于“每年平均天数”的稍微更准确的数字是365.2425。
这是一个全面的解决方案，返回一个类似于TimeSpan的DateTimeSpan ，除了它包含除时间组件之外的所有日期组件。
用法：
void Main()
{
DateTime compareTo = DateTime.Parse("8/13/2010 8:33:21 AM");
DateTime now = DateTime.Parse("2/9/2012 10:10:11 AM");
var dateSpan = DateTimeSpan.CompareDates(compareTo, now);
Console.WriteLine("Years: " + dateSpan.Years);
Console.WriteLine("Months: " + dateSpan.Months);
Console.WriteLine("Days: " + dateSpan.Days);
Console.WriteLine("Hours: " + dateSpan.Hours);
Console.WriteLine("Minutes: " + dateSpan.Minutes);
Console.WriteLine("Seconds: " + dateSpan.Seconds);
Console.WriteLine("Milliseconds: " + dateSpan.Milliseconds);
}
输出：
年份：1
几个月：5
天：27
营业时间：1
分钟：36
秒：50
毫秒：0
为了方便起见，我将逻辑放入了DateTimeSpan结构中，但您可以将方法CompareDates移动到您认为合适的地方。 还要注意，哪个日期在另一个之前是无关紧要的。
public struct DateTimeSpan
{
private readonly int years;
private readonly int months;
private readonly int days;
private readonly int hours;
private readonly int minutes;
private readonly int seconds;
private readonly int milliseconds;
public DateTimeSpan(int years, int months, int days, int hours, int minutes, int seconds, int milliseconds)
{
this.years = years;
this.months = months;
this.days = days;
this.hours = hours;
this.minutes = minutes;
this.seconds = seconds;
this.milliseconds = milliseconds;
}
public int Years { get { return years; } }
public int Months { get { return months; } }
public int Days { get { return days; } }
public int Hours { get { return hours; } }
public int Minutes { get { return minutes; } }
public int Seconds { get { return seconds; } }
public int Milliseconds { get { return milliseconds; } }
enum Phase { Years, Months, Days, Done }
public static DateTimeSpan CompareDates(DateTime date1, DateTime date2)
{
if (date2 < date1)
{
var sub = date1;
date1 = date2;
date2 = sub;
}
DateTime current = date1;
int years = 0;
int months = 0;
int days = 0;
Phase phase = Phase.Years;
DateTimeSpan span = new DateTimeSpan();
int officialDay = current.Day;
while (phase != Phase.Done)
{
switch (phase)
{
case Phase.Years:
if (current.AddYears(years + 1) > date2)
{
phase = Phase.Months;
current = current.AddYears(years);
}
else
{
years++;
}
break;
case Phase.Months:
if (current.AddMonths(months + 1) > date2)
{
phase = Phase.Days;
current = current.AddMonths(months);
if (current.Day < officialDay && officialDay <= DateTime.DaysInMonth(current.Year, current.Month))
current = current.AddDays(officialDay - current.Day);
}
else
{
months++;
}
break;
case Phase.Days:
if (current.AddDays(days + 1) > date2)
{
current = current.AddDays(days);
var timespan = date2 - current;
span = new DateTimeSpan(years, months, days, timespan.Hours, timespan.Minutes, timespan.Seconds, timespan.Milliseconds);
phase = Phase.Done;
}
else
{
days++;
}
break;
}
}
return span;
}
}
如果你想要满月的确切数量，总是肯定的（2000-01-15，2000-02-14返回0），考虑到整个月是你到达下一个月的同一天（类似年龄计算）
public static int GetMonthsBetween(DateTime from, DateTime to)
{
if (from > to) return GetMonthsBetween(to, from);
var monthDiff = Math.Abs((to.Year * 12 + (to.Month - 1)) - (from.Year * 12 + (from.Month - 1)));
if (from.AddMonths(monthDiff) > to || to.Day < from.Day)
{
return monthDiff - 1;
}
else
{
return monthDiff;
}
}
编辑原因：旧代码在某些情况下不正确：
new { From = new DateTime(1900, 8, 31), To = new DateTime(1901, 8, 30), Result = 11 },
Test cases I used to test the function:
var tests = new[]
{
new { From = new DateTime(1900, 1, 1), To = new DateTime(1900, 1, 1), Result = 0 },
new { From = new DateTime(1900, 1, 1), To = new DateTime(1900, 1, 2), Result = 0 },
new { From = new DateTime(1900, 1, 2), To = new DateTime(1900, 1, 1), Result = 0 },
new { From = new DateTime(1900, 1, 1), To = new DateTime(1900, 2, 1), Result = 1 },
new { From = new DateTime(1900, 2, 1), To = new DateTime(1900, 1, 1), Result = 1 },
new { From = new DateTime(1900, 1, 31), To = new DateTime(1900, 2, 1), Result = 0 },
new { From = new DateTime(1900, 8, 31), To = new DateTime(1900, 9, 30), Result = 0 },
new { From = new DateTime(1900, 8, 31), To = new DateTime(1900, 10, 1), Result = 1 },
new { From = new DateTime(1900, 1, 1), To = new DateTime(1901, 1, 1), Result = 12 },
new { From = new DateTime(1900, 1, 1), To = new DateTime(1911, 1, 1), Result = 132 },
new { From = new DateTime(1900, 8, 31), To = new DateTime(1901, 8, 30), Result = 11 },
};