给定代表某人生日的DateTime,我如何计算他们的年龄(以年为单位)?
当前回答
这是一个非常适合我的功能。没有计算,非常简单。
public static string ToAge(this DateTime dob, DateTime? toDate = null)
{
if (!toDate.HasValue)
toDate = DateTime.Now;
var now = toDate.Value;
if (now.CompareTo(dob) < 0)
return "Future date";
int years = now.Year - dob.Year;
int months = now.Month - dob.Month;
int days = now.Day - dob.Day;
if (days < 0)
{
months--;
days = DateTime.DaysInMonth(dob.Year, dob.Month) - dob.Day + now.Day;
}
if (months < 0)
{
years--;
months = 12 + months;
}
return string.Format("{0} year(s), {1} month(s), {2} days(s)",
years,
months,
days);
}
这里是一个单元测试:
[Test]
public void ToAgeTests()
{
var date = new DateTime(2000, 1, 1);
Assert.AreEqual("0 year(s), 0 month(s), 1 days(s)", new DateTime(1999, 12, 31).ToAge(date));
Assert.AreEqual("0 year(s), 0 month(s), 0 days(s)", new DateTime(2000, 1, 1).ToAge(date));
Assert.AreEqual("1 year(s), 0 month(s), 0 days(s)", new DateTime(1999, 1, 1).ToAge(date));
Assert.AreEqual("0 year(s), 11 month(s), 0 days(s)", new DateTime(1999, 2, 1).ToAge(date));
Assert.AreEqual("0 year(s), 10 month(s), 25 days(s)", new DateTime(1999, 2, 4).ToAge(date));
Assert.AreEqual("0 year(s), 10 month(s), 1 days(s)", new DateTime(1999, 2, 28).ToAge(date));
date = new DateTime(2000, 2, 15);
Assert.AreEqual("0 year(s), 0 month(s), 28 days(s)", new DateTime(2000, 1, 18).ToAge(date));
}
其他回答
这为这个问题提供了“更多细节”。也许这就是你要找的
DateTime birth = new DateTime(1974, 8, 29);
DateTime today = DateTime.Now;
TimeSpan span = today - birth;
DateTime age = DateTime.MinValue + span;
// Make adjustment due to MinValue equalling 1/1/1
int years = age.Year - 1;
int months = age.Month - 1;
int days = age.Day - 1;
// Print out not only how many years old they are but give months and days as well
Console.Write("{0} years, {1} months, {2} days", years, months, days);
private int GetYearDiff(DateTime start, DateTime end)
{
int diff = end.Year - start.Year;
if (end.DayOfYear < start.DayOfYear) { diff -= 1; }
return diff;
}
[Fact]
public void GetYearDiff_WhenCalls_ShouldReturnCorrectYearDiff()
{
//arrange
var now = DateTime.Now;
//act
//assert
Assert.Equal(24, GetYearDiff(new DateTime(1992, 7, 9), now)); // passed
Assert.Equal(24, GetYearDiff(new DateTime(1992, now.Month, now.Day), now)); // passed
Assert.Equal(23, GetYearDiff(new DateTime(1992, 12, 9), now)); // passed
}
我找到的最简单的方法就是这样。它适用于美国和西欧地区。无法与其他地区通话,尤其是中国这样的地方。在最初计算年龄后,最多可额外进行4次比较。
public int AgeInYears(DateTime birthDate, DateTime referenceDate)
{
Debug.Assert(referenceDate >= birthDate,
"birth date must be on or prior to the reference date");
DateTime birth = birthDate.Date;
DateTime reference = referenceDate.Date;
int years = (reference.Year - birth.Year);
//
// an offset of -1 is applied if the birth date has
// not yet occurred in the current year.
//
if (reference.Month > birth.Month);
else if (reference.Month < birth.Month)
--years;
else // in birth month
{
if (reference.Day < birth.Day)
--years;
}
return years ;
}
我仔细查看了答案,发现没有人提及闰日出生的监管/法律影响。例如,根据维基百科,如果你在2月29日出生在不同的司法管辖区,你的非闰年生日会有所不同:
在英国和香港:这是一年中的第几天,所以第二天,3月1日是你的生日。在新西兰:这是前一天,2月28日用于驾驶执照,3月1日用于其他目的。台湾:今天是2月28日。
据我所知,在美国,法规对此事保持沉默,这取决于普通法以及各个监管机构如何在其法规中定义事物。
为此,需要改进:
public enum LeapDayRule
{
OrdinalDay = 1 ,
LastDayOfMonth = 2 ,
}
static int ComputeAgeInYears(DateTime birth, DateTime reference, LeapYearBirthdayRule ruleInEffect)
{
bool isLeapYearBirthday = CultureInfo.CurrentCulture.Calendar.IsLeapDay(birth.Year, birth.Month, birth.Day);
DateTime cutoff;
if (isLeapYearBirthday && !DateTime.IsLeapYear(reference.Year))
{
switch (ruleInEffect)
{
case LeapDayRule.OrdinalDay:
cutoff = new DateTime(reference.Year, 1, 1)
.AddDays(birth.DayOfYear - 1);
break;
case LeapDayRule.LastDayOfMonth:
cutoff = new DateTime(reference.Year, birth.Month, 1)
.AddMonths(1)
.AddDays(-1);
break;
default:
throw new InvalidOperationException();
}
}
else
{
cutoff = new DateTime(reference.Year, birth.Month, birth.Day);
}
int age = (reference.Year - birth.Year) + (reference >= cutoff ? 0 : -1);
return age < 0 ? 0 : age;
}
需要注意的是,该代码假设:
西方(欧洲)对年龄的推算,以及一种日历,如公历,在月底插入一个闰日。
因为闰年和所有事情,我知道的最好的方法是:
DateTime birthDate = new DateTime(2000,3,1);
int age = (int)Math.Floor((DateTime.Now - birthDate).TotalDays / 365.25D);
下面是一个测试片段:
DateTime bDay = new DateTime(2000, 2, 29);
DateTime now = new DateTime(2009, 2, 28);
MessageBox.Show(string.Format("Test {0} {1} {2}",
CalculateAgeWrong1(bDay, now), // outputs 9
CalculateAgeWrong2(bDay, now), // outputs 9
CalculateAgeCorrect(bDay, now), // outputs 8
CalculateAgeCorrect2(bDay, now))); // outputs 8
这里有一些方法:
public int CalculateAgeWrong1(DateTime birthDate, DateTime now)
{
return new DateTime(now.Subtract(birthDate).Ticks).Year - 1;
}
public int CalculateAgeWrong2(DateTime birthDate, DateTime now)
{
int age = now.Year - birthDate.Year;
if (now < birthDate.AddYears(age))
age--;
return age;
}
public int CalculateAgeCorrect(DateTime birthDate, DateTime now)
{
int age = now.Year - birthDate.Year;
if (now.Month < birthDate.Month || (now.Month == birthDate.Month && now.Day < birthDate.Day))
age--;
return age;
}
public int CalculateAgeCorrect2(DateTime birthDate, DateTime now)
{
int age = now.Year - birthDate.Year;
// For leap years we need this
if (birthDate > now.AddYears(-age))
age--;
// Don't use:
// if (birthDate.AddYears(age) > now)
// age--;
return age;
}
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