如何检查System :: Collections：ArrayList是否为空/ nullptr / null？ [英] How do I check if System::Collections:ArrayList is empty / nullptr / null?

问题描述

我想知道在C ++ / CLI中如何检查ArrayList是否存在。

  System :: Collections :: ArrayList％queue_tx 
  

我试过 if（nullptr！= queue_tx）{queue_tx.Add（msg）; } 但是没有工作。我将 queue_tx 作为参数传递给一个函数，并且应该有这个参数不被设置的可能性（或被设置为 nullptr ）。

编译器抛出'！='：没有从'System :: Collections :: ArrayList' 'nullptr'。

如何做到这一点？

解决方案

％定义引用变量，这是为什么它不能为空

已经这样声明了ArrayList：

  System :: Collections :: ArrayList ^ queue_tx 
  
 
 
 
那么你的nullptr检查是可能的，并且有一个意义
 
 
 
 code> queue_tx.Count（）以检查集合是否为空
 
 
 
我会建议过去：
 
 
 
 引用和指针变量之间的差异 
 
 
 
 何时使用引用VS指针 
 
I'd like to know how in C++/CLI it is possible to check whether an ArrayList is existent. 
System::Collections::ArrayList %queue_tx
I tried if ( nullptr != queue_tx ) { queue_tx.Add(msg); } but that didn't work. I'm passing queue_tx as a parameter to a function and there's supposed to be the possibility of this parameter not being set (or being set to nullptr).

The compiler throws '!=' : no conversion from 'System::Collections::ArrayList' to 'nullptr'.

How do I do this?
解决方案
% defines a reference variable this is why it cannot be null 

if you would have declared the ArrayList like this:
System::Collections::ArrayList^ queue_tx
then your nullptr check would be possible and have a meaning 

otherwise just use the queue_tx.Count() to check if the collection is empty

I would recommend going over:

the difference between reference and pointer variables

When to use a Reference VS Pointers

                        
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