how to implement a class in c [duplicate]

by

There are no classes in C, only structs. There are classes in C++.

There is also no private:

struct A
{
   int a, b;
   int c, d;
   int e, f;
};

void func1( struct A* );

void fun( struct A* );

But everything is public.

In order to make things more encapsulated, you would hide the actual implementation detail of struct A and show just a forward declaration with the public methods.

protected makes no real sense as there is no inheritance. You can sort-of implement “friendship” by exposing your detail or its functionality to certain internal modules but friendship is not the same as protected, which simply can’t exist within C.

In your class you have made two of the members public but if we “hide” struct A we hide everything, so provide getters and setters instead.

Alternatively we can “hide” part of our struct, something like:
struct A1;

struct A
{
   struct A1 * privatePart;
   int b, c;  // public part     
};

although it gets “messy” as you have to start allocating the private part (and remember in C there are no smart pointers or destructors so you’ll have to be a lot more careful with memory management).

What a lot of C APIs use for this is a naming convention whereby they call “private” variables “reserved”, often reserved1, reserved2 etc. The compiler won’t stop you writing to them, but you obviously do so at your own risk, and the intention is clear that you are not supposed to access these members (other than direct copying or similar).

More Related Contents:

  1. What exactly is nullptr?
  2. How to determine if a string is a number with C++?
  3. Base64 decode snippet in C++
  4. Create Random Number Sequence with No Repeats
  5. Why can’t variable names start with numbers?
  6. printf with std::string?
  7. Why don’t compilers merge redundant std::atomic writes?
  8. Printing 1 to 1000 without loop or conditionals
  9. How should I deal with mutexes in movable types in C++?
  10. How do I check if a C++ std::string starts with a certain string, and convert a substring to an int?
  11. lifetime of a std::initializer_list return value
  12. C++ How to detect Windows 10
  13. May I take the address of the one-past-the-end element of an array? [duplicate]
  14. Brace-enclosed initializer list constructor
  15. error LNK2005: already defined – C++
  16. Where can I use alignas() in C++11?
  17. c++ lambdas how to capture variadic parameter pack from the upper scope
  18. Why use a const member function?
  19. Why does valgrind say basic SDL program is leaking memory?
  20. What is a ‘thunk’?
  21. Converting string of 1s and 0s into binary value
  22. Cast to int vs floor
  23. Why cast a pointer to a float into a pointer to a long, then dereference?
  24. Why can’t I replace std::map with std::unordered_map
  25. How should one use std::optional?
  26. Can I use Qt without qmake or Qt Creator?
  27. OpenCV Edge/Border detection based on color
  28. Breaking ReadFile() blocking – Named Pipe (Windows API)
  29. Different execution policies at runtime
  30. How to test an EXE with Google Test?

Leave a Comment