blocks|key|1462306|text|那么，使用指针的原因与在C中使用与malloc一起分配的指针的原因是完全相同的:如果您希望您的对象比您的变量存在更长的时间！|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1462307|如果可以避免使用new运算符，甚至强烈建议您不要使用它。特别是当你使用异常的时候。一般来说，让编译器释放你的对象要安全得多。|1462308|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Well, the reason to use the pointer would be exactly the same that the reason to use pointers in C allocated with malloc: if you want your object to live longer than your variable!

It is even highly recommended to NOT use the new operator if you can avoid it. Especially if you use exceptions. In general it is much safer to let the compiler free your objects.

blocks|key|1462383|text|我担心的唯一原因是Dog现在被分配在堆栈上，而不是堆上。所以如果Dog的大小是兆字节，你可能会有问题，|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1462384|如果您确实需要使用new/delete路径，则要小心异常。因此，您应该使用auto_ptr或boost智能指针类型之一来管理对象生存期。|1462385|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

The only reason I'd worry about is that Dog is now allocated on the stack, rather than the heap. So if Dog is megabytes in size, you may have a problem,

If you do need to go the new/delete route, be wary of exceptions. And because of this you should use auto_ptr or one of the boost smart pointer types to manage the object lifetime.

blocks|key|1462447|text|当您可以在堆栈上进行分配时，没有理由使用new+(在堆上)(除非由于某种原因，您有一个很小的堆栈，并且想要使用堆。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1462448|如果您确实希望在堆上进行分配，则可能需要考虑使用标准库中的shared_ptr+(或其变体之一)。一旦所有对shared_ptr的引用都不复存在，它将为您处理删除操作。|1462449|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

There's no reason to new (on the heap) when you can allocate on the stack (unless for some reason you've got a small stack and want to use the heap.

You might want to consider using a shared_ptr (or one of its variants) from the standard library if you do want to allocate on the heap. That'll handle doing the delete for you once all references to the shared_ptr have gone out of existance.

blocks|key|1677616|text|我见过这种反模式来自那些不太理解&+address-of运算符的人。如果他们需要调用一个带指针的函数，他们总是会在堆上分配，这样他们就会得到一个指针。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1677617|void+FeedTheDog(Dog*+hungryDog);

Dog*+badDog+=+new+Dog;
FeedTheDog(badDog);
delete+badDog;

Dog+goodDog;
FeedTheDog(&goodDog);|code-block|syntax|javascript|1677618|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|$]]

I've seen this anti-pattern from people who don't quite get the &amp; address-of operator. If they need to call a function with a pointer, they'll always allocate on the heap so they get a pointer.

<pre><code>void FeedTheDog(Dog* hungryDog);

Dog* badDog = new Dog;
FeedTheDog(badDog);
delete badDog;

Dog goodDog;
FeedTheDog(&amp;goodDog);
</code></pre>

blocks|key|1677649|text|我在Visual+Studio中也遇到了同样的问题。你必须使用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1677650|你的yourClass>classMethod()；|1677651|而不是：|1677652|yourClass.classMethod()；|1677653|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

I had the same problem in Visual Studio. You have to use:

yourClass->classMethod();

rather than:

yourClass.classMethod();

blocks|key|1462580|text|还有一个其他人没有提到的原因，那就是为什么您可能选择动态创建对象。动态的、基于堆的对象允许您使用polymorphism。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1462581|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/1031273/what-is-polymorphism^0|1C|C|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

There is an additional reason, which no one else has mentioned, why you might choose to create your object dynamically. Dynamic, heap based objects allow you to make use of <a href="https://stackoverflow.com/questions/1031273/what-is-polymorphism">polymorphism</a>.

I'm a C programmer trying to understand C++. Many tutorials demonstrate object instantiation using a snippet such as:

<pre><code>Dog* sparky = new Dog();
</code></pre>

which implies that later on you'll do:

<pre><code>delete sparky;
</code></pre>

which makes sense. Now, in the case when dynamic memory allocation is unnecessary, is there any reason to use the above instead of

<pre><code>Dog sparky;
</code></pre>

and let the destructor be called once sparky goes out of scope?

Thanks!

C++ Object Instantiation

Visual Studio

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我是一个试图理解C++的C程序员。许多教程使用以下代码片段演示对象实例化：Dog* sparky = new Dog();这意味着稍后您将执行以下操作：delete sparky;这是有道理的。现在，在不需要动态内存分配的情况下，有没有理由使用上面的方法而不是Dog sparky;一旦sparky超出作用域，就让析构函...

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