隐藏成员C结构 [英] Hiding members in a C struct

问题描述

我一直在阅读有关用C OOP，但我从来不喜欢你怎么不具有私有数据成员像您可以在C ++中。但随后来到了我的脑海里，你可以创建2的结构。一个是在头文件中定义，而另一个是在源文件中所定义

I've been reading about OOP in C but I never liked how you can't have private data members like you can in C++. But then it came to my mind that you could create 2 structures. One is defined in the header file and the other is defined in the source file.

// =========================================
// in somestruct.h
typedef struct {
  int _public_member;
} SomeStruct;

// =========================================
// in somestruct.c

#include "somestruct.h"

typedef struct {
  int _public_member;
  int _private_member;
} SomeStructSource;

SomeStruct *SomeStruct_Create()
{
  SomeStructSource *p = (SomeStructSource *)malloc(sizeof(SomeStructSource));
  p->_private_member = 42;
  return (SomeStruct *)p;
}

从这里你可以只投一种结构到其他。
这被认为是不好的做法？抑或是常做？

From here you can just cast one structure to the other. Is this considered bad practice? Or is it done often?

推荐答案

个人而言，我更喜欢这样的：

Personally, I'd more like this:

typedef struct {
  int _public_member;
  /*I know you wont listen, but don't ever touch this member.*/
  int _private_member;
} SomeStructSource;

这是Ç毕竟，如果人们想搞砸了，他们应该被允许 - 没有必要隐瞒的东西，除了：

It's C after all, if people want to screw up, they should be allowed to - no need to hide stuff, except:

如果你需要的是保持ABI / API兼容，还有这是比较常见的，从我所看到的2的方法。

If what you need is to keep the ABI/API compatible, there's 2 approaches that's more common from what I've seen.

• 不要给你的客户端访问结构，给他们一个不透明的句柄（一个void *用pretty名），提供初始化/销毁和存取功能应有尽有。这可以确保您可以更改
  结构甚至没有重新编译的客户，如果你正在编写一个库。

• Don't give your clients access to the struct, give them an opaque handle (a void* with a pretty name), provide init/destroy and accessor functions for everything. This makes sure you can change the structure without even recompiling the clients if you're writing a library.

提供一个不透明的句柄作为你的结构，你可以分配但是你喜欢的一部分。这种方法即使在C ++来提供的ABI兼容性。

provide an opaque handle as part of your struct, which you can allocate however you like. This approach is even used in C++ to provide ABI compatibility.

例如

 struct SomeStruct {
  int member;
  void* internals; //allocate this to your private struct
 };

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