C＃中的DateTime.AddDays()方法

此方法用于返回一个新的DateTime，该日期将指定的天数添加到此实例的值中。

句法：

public DateTime AddDays (double value);

在这里，该值是整天和小数天数。值参数可以为负或正。

返回值：该方法返回一个对象，该对象的值是此实例表示的日期和时间与value表示的天数之和。

异常：如果生成的DateTime小于MinValue或大于MaxValue，则此方法将提供ArgumentOutOfRangeException 。

下面的程序说明了DateTime.AddDays(Double)方法的用法：

范例1：

// C# program to demonstrate the
// DateTime.AddDays(Double) Method
using System;
using System.Globalization;
  
class GFG {
  
    // Main Method
    public static void Main()
    {
        try {
  
            // creating object of DateTime
            DateTime date1 = new DateTime(2010, 1, 1,
                                           8, 0, 15);
  
            // adding the 36 days
            // using AddDays() method;
            DateTime date2 = date1.AddDays(36);
  
            // Display the date1
            System.Console.WriteLine("DateTime before "+
                      "operation: {0:y} {0:dd}", date1);
  
            // Display the date2
            System.Console.WriteLine("\nDateTime after"+
                     " operation: {0:y} {0:dd}", date2);
        }
  
        catch (ArgumentOutOfRangeException e) 
        {
            Console.Write("Exception Thrown: ");
            Console.Write("{0}", e.GetType(), e.Message);
        }
    }
}

输出：

DateTime before operation: 2010 January 01

DateTime after operation: 2010 February 06

示例2：对于ArgumentOutOfRangeException

// C# program to demonstrate the
// DateTime.AddDays(Double) Method
using System;
using System.Globalization;
  
class GFG {
  
    // Main Method
    public static void Main()
    {
        try {
  
            // creating object of DateTime and
            // initialize with MinValue
            DateTime date1 = DateTime.MaxValue;
  
            // Display the date1
            Console.WriteLine("DateTime before "+
               "operation: {0:y} {0:dd}", date1);
  
            // adding the TimeSpan of 36 days
            // using Add() method;
            System.DateTime date2 = date1.AddDays(36);
  
            // Display the date2
            System.Console.WriteLine("\nDateTime after "+
                       "operation: {0:y} {0:dd}", date2);
        }
  
        catch (ArgumentOutOfRangeException e) 
        {
            Console.WriteLine("\nThe resulting DateTime is "+
                       "greater than the DateTime.MaxValue ");
  
            Console.Write("Exception Thrown: ");
            Console.Write("{0}", e.GetType(), e.Message);
        }
    }
}

输出：

DateTime before operation: 9999 December 31

The resulting DateTime is greater than the DateTime.MaxValue 
Exception Thrown: System.ArgumentOutOfRangeException

笔记：

• 此方法不会更改此DateTime的值。而是返回一个新的DateTime，其值是此操作的结果。
• 值的小数部分是一分钟的小数部分。例如，7.5等于7分钟，30秒，0毫秒和0个滴答。
• value参数将四舍五入到最接近的毫秒数。

参考：

• https://docs.microsoft.com/zh-cn/dotnet/api/system.datetime.adddays?view=netframework-4.7.2