LINQ总和OverflowException异常？ [英] LINQ Sum OverflowException?

问题描述

我已经实现了EventLogEntry一个自定义的IEqualityComparer

 公共类EventLogEntryListComparison：
的IEqualityComparer<名单< EventLogEntry> ;>中
的IEqualityComparer< EventLogEntry> 
  

有关的IEqualityComparer<名单< EventLogEntry>> 的GetHashCode的功能很简单

 公众诠释的GetHashCode（列表< EventLogEntry> OBJ）
 {
返回obj.Sum（入门= GT; 23 *的GetHashCode（入门））; 
} 
  

不过，这将引发对某些项的发生OverflowException。

 算术运算导致溢出。 
在System.Linq.Enumerable.Sum（IEnumerable`1源）
在System.Linq.Enumerable.Sum [TSource]（IEnumerable`1源，Func`2选择器）
 AT< ;剪断> .Diagnostics.EventLogAnalysis.EventLogEntryListComparison.GetHashCode（List`1 OBJ）在C：\dev\<&剪断GT; Diagnostics.EventLogAnalysis\EventLogEntryListComparison.cs：行112 
。在System.Collections.Generic .Dictionary`2.Insert（TKEY的关键，TValue值，布尔加）在System.Collections.Generic.Dictionary`2.set_Item 
（TKEY的关键，TValue值）
 AT<&剪断GT; .Diagnostics .EventLogAnalysis.Program.AnalyseMachine（字符串validMachineName）在C：\dev\<&剪断GT; .Diagnostics.EventLogAnalysis\Program.cs：行104 
在System.Threading.Tasks.Parallel其中p;> ; c__DisplayClass2d`2&所述。ForEachWorker方式> b__23（的Int32ⅰ）
。在System.Threading.Tasks.Parallel&下;> c__DisplayClassf`1&所述。ForWorker> b__c（）
  

试图让同样的错误，而调试和不能在即时窗口，我改变了代码，这个和再见OverflowException异常后？

  INT总= 0; 
的foreach（OBJ中VAR eventLogEntry）
 {
总+ =的GetHashCode（eventLogEntry）; 
} 
 
总回报; 
  

它是如何LINQ的Sum函数表现不同？

编辑2

由于采用了一些意见，校正并打算GetHashCode的功能如下内容，

 公众诠释的GetHashCode（列表< EventLogEntry> OBJ）
 {
返回选中（obj.Aggregate（17，
（累积，条目）= GT; 
累加* 23 +的GetHashCode（条目）））; 
} 
  

解决方案

LINQ的 Enumerable.Sum（...）方法执行检查块内的补充。这意味着，如果总和溢出，他们故意抛出异常。

您和是不是检查块内，所以不论它抛出一个异常要看...无论是从一个叫检查块，或者我相信大会的属性里面。

I've implemented a custom IEqualityComparer for EventLogEntry.

public class EventLogEntryListComparison :
    IEqualityComparer<List<EventLogEntry>>,
    IEqualityComparer<EventLogEntry>

For IEqualityComparer<List<EventLogEntry>>, the GetHashCode function is very simple.

public int GetHashCode(List<EventLogEntry> obj)
{
    return obj.Sum(entry => 23 * GetHashCode(entry));
}

However, this throws an OverflowException for certain entries.

"Arithmetic operation resulted in an overflow."
   at System.Linq.Enumerable.Sum(IEnumerable`1 source)
   at System.Linq.Enumerable.Sum[TSource](IEnumerable`1 source, Func`2 selector)
   at <snip>.Diagnostics.EventLogAnalysis.EventLogEntryListComparison.GetHashCode(List`1 obj) in C:\dev\<snip>Diagnostics.EventLogAnalysis\EventLogEntryListComparison.cs:line 112
   at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
   at System.Collections.Generic.Dictionary`2.set_Item(TKey key, TValue value)
   at <snip>.Diagnostics.EventLogAnalysis.Program.AnalyseMachine(String validMachineName) in C:\dev\<snip>.Diagnostics.EventLogAnalysis\Program.cs:line 104
   at System.Threading.Tasks.Parallel.<>c__DisplayClass2d`2.<ForEachWorker>b__23(Int32 i)
   at System.Threading.Tasks.Parallel.<>c__DisplayClassf`1.<ForWorker>b__c()

After trying to get the same error whilst debugging and couldn't in the immediate window, I changed the code to this and bye bye OverflowException?

int total = 0;
foreach (var eventLogEntry in obj)
{
    total += GetHashCode(eventLogEntry);
}

return total;

How is it that LINQ's Sum function behaving differently?

Edit 2

Thanks to a few comments, the corrected and intended GetHashCode function is now as follows,

public int GetHashCode(List<EventLogEntry> obj)
{
    return unchecked(obj.Aggregate(17,
        (accumulate, entry) =>
        accumulate * 23 + GetHashCode(entry)));
}

解决方案

LINQ's Enumerable.Sum(...) methods perform the additions inside a checked block. This means that they deliberately throw an exception if the sum overflows.

Your sum is not inside a checked block, so whether or not it throws an exception depends on... whether it is called from inside a checked block, or a property on the assembly I believe.

这篇关于LINQ总和OverflowException异常？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！