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

问题描述

我一直在阅读 C 语言中的 OOP，但我从不喜欢你不能像在 C++ 中那样拥有私有数据成员.但后来我想到你可以创建 2 个结构.一个在头文件中定义，另一个在源文件中定义.

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;
}

从这里您可以将一个结构投射到另一个结构上.这被认为是不好的做法吗?还是经常做?

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

就我个人而言，我更喜欢这样:

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;

毕竟是 C，如果人们想搞砸，他们应该被允许 - 不需要隐藏东西，除了:

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

如果您需要保持 ABI/API 兼容，有两种方法比我所见更常见.

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

• 不要让你的客户访问结构体，给他们一个不透明的句柄(一个有漂亮名字的 void*)，为所有东西提供 init/destroy 和 accessor 函数.这确保你可以改变如果您正在编写一个库，甚至不需要重新编译客户端的结构.

• 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.

提供一个不透明句柄作为结构的一部分，您可以随意分配.这种方法甚至用于 C++ 以提供 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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