C++：使用 memset 还是结构构造函数？什么是最快的？

发布于 2024-11-16 10:04:23 字数 1296 浏览 3 评论 0原文

我无法确定 C++ 中哪个更好：

我使用一个结构来管理消息队列中的客户端，该结构如下所示：

typedef struct _MsgClient {
  int handle;
  int message_class;
  void *callback;
  void *private_data;
  int priority;
} MsgClient;

所有这些都是 POD 实体。

现在，我有一个由这些结构组成的数组，用于存储我的客户端（我使用数组来限制内存，我必须限制碎片）。所以在我的课堂上，我有这样的内容：

class Foo
{
private:
  MsgClient _clients[32]; 

public:
  Foo()
  {
     memset(_clients, 0x0, sizeof(_clients));
  }

}

现在，我到处读到，在 C++ 中使用 memset 是不好的，而且我宁愿为我的结构使用构造函数。我想了这样的事情：

typedef struct _MsgClient {
  int handle;
  int message_class;
  void *callback;
  void *private_data;
  int priority;
  // struct constructor
  _MsgClient(): handle(0), message_class(0), callback(NULL), private_data(NULL), priority(0) {};
} MsgClient;

...将消除对memset的需要。但我担心的是，当初始化 foo 时，结构构造函数将被调用 32 次，而不是将其优化为简单的从数组占用的内存中清零。

您对此有何看法？
我刚刚发现这个：可以在不调用 memset 的情况下从构造函数初始值设定项列表中对成员结构进行零初始化吗？，它适合我的情况吗（这是不同的：我有一个数组，而不是该结构的单个实例）？
另外，根据这篇文章，向我的结构会自动将其转换为非POD结构，是吗？

原文

I'm having trouble figuring out which is better in C++:

I use a struct to manage clients in a message queue, the struct looks like this:

typedef struct _MsgClient {
  int handle;
  int message_class;
  void *callback;
  void *private_data;
  int priority;
} MsgClient;

All of these being POD entities.

Now, I have an array of these structs where I store my clients (I use an array for memory constraints, I have to limit fragmentation). So in my class I have something like this:

class Foo
{
private:
  MsgClient _clients[32]; 

public:
  Foo()
  {
     memset(_clients, 0x0, sizeof(_clients));
  }

}

Now, I read here and there on SO that using memset is bad in C++, and that I'd rather use a constructor for my structure.
I figured something like this:

typedef struct _MsgClient {
  int handle;
  int message_class;
  void *callback;
  void *private_data;
  int priority;
  // struct constructor
  _MsgClient(): handle(0), message_class(0), callback(NULL), private_data(NULL), priority(0) {};
} MsgClient;

...would eliminate the need of the memset. But my fear is that when foo is initialized, the struct constructor will be called 32 times, instead of optimizing it as a simple zero out of the memory taken by the array.

What's your opinion on this?
I just found this: Can a member struct be zero-init from the constructor initializer list without calling memset? , is it appropriate in my case (which is different: I have an array, not a single instance of the structure)?
Also, according to this post, adding a constructor to my structure will automatically convert it into a non-POD structure, is it right?

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浅黛梨妆こ 2024-11-23 10:04:23

在一致的实现上，使用空成员初始值设定项对构造函数初始值设定项列表中的数组进行值初始化是完全有效的。对于数组成员，这将产生每个数组元素的成员零初始化的效果。

编译器应该能够使其非常高效，并且您无需向 struct 添加构造函数。

例如

Foo() : _clients() {}

On a conforming implementation, it's perfectly valid to value-initialize an array in the constructor initializer list with an empty member initializer. For your array members, this will have the effect of zero-initializing the members of each array element.

The compiler should be able to make this very efficient and there's no need for you to add a constructor to your struct.

E.g.