blocks|key|3203458|text|尝试更改数组的大小：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3203459|student[]+arr+=+new+student[2];|code-block|syntax|javascript|3203460|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Try changing the size of the array:

<pre><code>student[] arr = new student[2];
</code></pre>

blocks|key|4670983|text|您有一个大小为3的数组，但您只添加了2个元素。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4670984|变化|4670985|student[]+arr+=+new+student[3];|code-block|syntax|javascript|4670986|至|4670987|student[]+arr+=+new+student[2];|4670988|这是因为您试图在student类尚未初始化时访问该类的成员。|offset|length|style|CODE|4670989|你可以像我上面说的那样做，或者添加第三个学生。|4670990|entityMap^0|0|0|0|0|0|8|7|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|11|8|@$O|12|P|13|Q|R]]|9|@]|A|$]]|$1|S|3|T|5|6|7|14|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

You have an array with the size of 3, but you only add 2 elements.

Change

<pre><code>student[] arr = new student[3];
</code></pre>

To

<pre><code>student[] arr = new student[2];
</code></pre>

This happens because you try to access members of the <code>student</code> class when it hasn't been initialized.

You could do as I said above or add a 3rd student.

blocks|key|3203490|text|尽管您没有很好地指出错误发生的确切位置，但是您发布的代码初始化了arr[0]和arr[1]，但从未初始化arr[2]。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3203491|因为您分配了一个具有三个元素的数组，所以最后可以从您的循环访问这三个元素。|3203492|因此，当您尝试访问最后一个元素的属性时，我预计会出现一个空引用异常。|3203493|entityMap^0|W|6|13|6|1G|6|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@$9|M|A|N|B|C]|$9|O|A|P|B|C]|$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|S|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|T|8|@]|D|@]|E|$]]|$1|J|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|K|$]]

Although you haven't done a good job of indicating where exactly the error is occurring, the code you've posted initialized <code>arr[0]</code> and <code>arr[1]</code>, but never initializes <code>arr[2]</code>.

Since you allocated an array with three elements, all three of them are accessed from your loop at the end.

Therefore, I would expect a null reference exception when you attempt to access the properties of this last element.

blocks|key|887734|text|您的数组大小为3，但您仅将2个元素初始化为数组。虽然arr和arr1中存在元素，但arr2会返回空引用，因为您没有在其中初始化任何数据。您可以使用以下命令将数据添加到arr2或将数组大小更改为2|type|unstyled|depth|inlineStyleRanges|entityRanges|data|887735|student[]+arr+=+new+student[2]|offset|length|style|CODE|887736|entityMap^0|0|0|U|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@$D|L|E|M|F|G]]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

Your array size is 3, but you have initialized only 2 elements to the array. While there are elements present in arr[0] and arr[1], arr[2] returns null reference as you have no data initialized there. You can add data to arr[2] or change the array size to 2 using

<code>student[] arr = new student[2]</code>

blocks|key|1045565|text|您之所以获得NullReferenceException，是因为您试图访问循环中一个空学生的属性(您只初始化了前两个，而没有初始化最后一个)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1045566|避免此异常的一种方法是在循环中执行null检查，因此如果您尚未初始化某些项，则仍然可以输出已初始化的学生的姓名：|1045567|foreach+(student+i+in+arr.Where(s+=>+s+!=+null))
{
++++Console.WriteLine("\nname:{0}\nmarks:{1}",+i._name,+i._marks);
}|code-block|syntax|javascript|1045568|您还可以仅显示实际具有名称的学生(通过检查是否为空名称)，如下所示：|1045569|foreach+(student+i+in+arr.Where(s+=>+s+!=+null+&&+s._name+!=+null))
{
++++Console.WriteLine("\nname:{0}\nmarks:{1}",+i._name,+i._marks);
}|1045570|但实际上，这样的事情可能应该在学生类本身中完成，这样客户端就不必这样做了。您可以考虑为学生类中的name设置一些默认值，这样如果没有设置，您仍然可以显示一些内容(比如"No+Name")，您还可以重写ToString()方法，以便学生类知道如何正确地显示自己。而且，在C#中，类和公共属性通常是PascalCase：|1045571|public+class+Student
{
++++private+string+_name;

++++public+string+Name
++++{+
++++++++get+{+return+_name;+}+
++++++++set+{+if+(value+!=+null)+_name+=+value;+}
++++}

++++public+int+Marks+{+get;+set;+}

++++public+Student()
++++{
++++++++Name+=+"<No+Name>";
++++}

++++public+override+string+ToString()
++++{
++++++++return+string.Format("{3}Name:{0}{3}Marks:{1}",+
++++++++++++Name,+Marks,+Environment.NewLine));
++++}
}|1045572|有了这些，你就可以做一些更简单的事情了，比如：|1045573|foreach+(student+i+in+arr.Where(s+=>+s+!=+null))
{
++++Console.WriteLine(i);
}|1045574|entityMap^0|6|M|0|0|0|0|0|2S|A|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|13|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|14|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|15|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|16|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@]|E|$]]|$1|S|3|T|5|J|7|1A|8|@]|D|@]|E|$K|L]]|$1|U|3|V|5|6|7|1B|8|@]|D|@]|E|$]]|$1|W|3|X|5|J|7|1C|8|@]|D|@]|E|$K|L]]|$1|Y|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|Z|$]]

You are getting the <code>NullReferenceException</code> because you're attempting to access the properties of a null student in your loop (you have only initialized the first two, but not the last one). 

One way to avoid this exception is to do a null check in your loop, so if you haven't initialized some of the items, you can still output the names of the students who have been initialized:

<pre><code>foreach (student i in arr.Where(s =&gt; s != null))
{
 Console.WriteLine("\nname:{0}\nmarks:{1}", i._name, i._marks);
}
</code></pre>

You could also only show students who actually have a name (by checking for a null name) like:

<pre><code>foreach (student i in arr.Where(s =&gt; s != null &amp;&amp; s._name != null))
{
 Console.WriteLine("\nname:{0}\nmarks:{1}", i._name, i._marks);
}
</code></pre>

But really something like this should probably be done in the student class itself, so the client doesn't have to. You might consider setting some default value for name in the student class, so if it isn't set you can still display something (like "No Name"), and you can also overwrite the <code>ToString()</code> method so that the student class knows how to display itself properly. And, while you're at it, classes and public properties are typically PascalCase in C#:

<pre><code>public class Student
{
 private string _name;

 public string Name
 { 
 get { return _name; } 
 set { if (value != null) _name = value; }
 }

 public int Marks { get; set; }

 public Student()
 {
 Name = "&lt;No Name&gt;";
 }

 public override string ToString()
 {
 return string.Format("{3}Name:{0}{3}Marks:{1}", 
 Name, Marks, Environment.NewLine));
 }
}
</code></pre>

With this in place, you can then do something simpler like:

<pre><code>foreach (student i in arr.Where(s =&gt; s != null))
{
 Console.WriteLine(i);
}
</code></pre>

I got null exception error while executing this program. Although I have initialize the array

<pre><code>public class student
{
 string name;

 public string _name
 {
 set
 {

 this.name = value;
 }
 get
 {
 return name;
 }
 }
 public int _marks{ set; get; }
}

student[] arr = new student[3];

arr[0] = new student();
arr[0]._name = "AB";
arr[0]._marks = 44;

arr[1] = new student();
arr[1]._name = "amla";
arr[1]._marks = 75;


foreach (student i in arr)
{
 Console.WriteLine("\nname:{0}\nmarks:{1}", i._name, i._marks);
}
Console.Read();
</code></pre>

get null reference exception after initialize the array

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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执行此程序时出现空异常错误。尽管我已经初始化了数组public class student{    string name;    public string _name    {        set        {            this.name = value;        }        get...

问初始化数组后出现空引用异常
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