略微混乱的指针情况 [英] Slightly confusing pointer situation

问题描述

我不完全确定指针在我创建的这种情况下是如何工作的，我小心避免内存泄漏。我写了以下代码;

Hi,

I'm not entirely sure how pointers work in this situation I've created and I'm being careful to avoid memory leaks. I've written the following code;

Packet* packet;

// construct packet from ID and data
switch (packet_id)
{
case 0:
	PacketPlayerMove* p = new PacketPlayerMove();
	// call some methods on p here which aren't present in base class Packet
	packet = p;
}

return packet;

所以PacketPlayerMove和其他许多人一样是基类Packet的实现。此方法返回Packet *，因此我创建Packet *并将其值指定为任何继承类的实例，具体取决于唯一标识符packet_id。



简而言之：



packet_id 0：返回PacketPlayerMove

packet_id 1：返回PacketPlayerChat

等



我不确定是否应该删除 p ，因为我不确定是否会这样做删除数据包，因为它的引用或值被复制 - 这是我的指针知识朦胧的地方。



我稍后会删除数据包，但我不知道我现在是否应该删除p，或者是否需要删除它。



我的尝试：



----------- ------------------------------------

So PacketPlayerMove and many others are implementations of the base class Packet. This method returns a Packet*, so I create a Packet* and assign its value as an instance of any of the inheriting classes, depending on a unique identifier packet_id.

In a nutshell:

packet_id 0: return PacketPlayerMove
packet_id 1: return PacketPlayerChat
etc.

I'm not sure whether I should delete p or not, because I'm not sure if that'll delete packet, as either its reference or value is copied - this is where my knowledge of pointers is hazy.

I will be deleting packet later, but I don't know whether I should delete p now, or if it doesn't need to be deleted.

What I have tried:

-----------------------------------------------

推荐答案

你也可以查看 C ++ 智能指针，例如参见intro/smart pointers - cppreference.com [ ^ ]。

You may also have a look at C++ smart pointers, see for instance intro/smart pointers - cppreference.com[^].

如果您稍后要删除指针，则不应该立即删除它。如果你复制了它，那么你可能会有内存泄漏。您应该能够测试它并检测内存泄漏。我在整个地方使用#define new DEBUG_NEW宏，并在调试模式下检测到泄漏。

If you are going to delete the pointer later then you should not delete it 'now'. If you have copied it then you will likely have a memory leak. You should be able to test this and detect a memory leak. I use the "#define new DEBUG_NEW" macro all over the place and leaks are detected in debug mode.

你必须明白指针变量就像一个普通变量。因此，您可以为它们分配不同的值，或为不同的指针分配相同的值。但是创建一个带有新的实例需要删除其他地方。

You must understand that a pointer variable is like a normal variable. So you can assign different values to them or the same value to different pointers. But creating an instance with new needs a delete somewhere else.

//some normal int var
int a = 2;
int b = a;

PacketPlayerMove* p = new PacketPlayerMove();//Pointer value NEEDS a delete
PacketPlayerMove* p2 = p;//no new instance only pointer assigment, so both pointers are pointing to the SAME address

delete p;// free the memory.

了解指针 C++教程。它有一些有趣的章节，里面有很多有趣的知识。



最好的做法是编写清晰易懂的代码，因为在处理大量指针时，很多东西都可以出错了。

Learn about pointers in this C++ tutorial. It has some interesting chapters packed with interesting knowledege.

It is best practice to write clear and understandable code, because when working with a lot of pointers a lot of things can go wrong.

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