structure "inheritance" in c

[darkenergy]

Hi all,

I want to do a similar thing as class inheritance in C++, but with structures in C.

I have a structure A, and I want to define a second structure B (in different .h/.c files), which has the same variables as A plus some additional ones. I want to use the existing functions that manipulate and create A also for B and, using some new functions, add the bits about the additional variables. If possible, it will not be necessary to change B and the new functions if A is modified.

Maybe some clever redefinitions using the prepcocessor can be used?

Thanks for your help,
Martin

[JosAH]

Hi all,

I want to do a similar thing as class inheritance in C++, but with structures in C.

I have a structure A, and I want to define a second structure B (in different .h/.c files), which has the same variables as A plus some additional ones. I want to use the existing functions that manipulate and create A also for B and, using some new functions, add the bits about the additional variables. If possible, it will not be necessary to change B and the new functions if A is modified.

Maybe some clever redefinitions using the prepcocessor can be used?

Thanks for your help,
Martin

In C a pointer to a struct can safely be casted to a pointer to the first element
of that struct and vice versa. The ANSI/ISO standard explicitly defined so. That
opens doors to do simple single inheritance emulation:

struct Base {
   ...
}
struct Derived {
   struct Base parent;
   ...
}

If you want to do virtual functions as well you have to make the first member
of your structs an array of pointers to functions. The tricky part will be the
initialization of such an array and the cpp fiddling necessary to reach such a
pointer to a function.

kind regards,

Jos

[weaknessforcats]

One of the secrets of C++ is that there are no classes. C++ is derived form C and in C the only syntax to define your own types with members is a struct. Classes have been implemented in C++ as structs.

That means:
1) you use inheritance with structs
2) you can have constructors/destructors with structs
3) virtual functions
4) etc... etc...

The only difference between a class and a struct is that the default access specifier for a class is private whereas the default for a struct is public. Therefore, if you specify public/private/protected for each one of your struct members, there is no difference between that and a class.

[JosAH]

One of the secrets of C++ is that there are no classes. C++ is derived form C and in C the only syntax to define your own types with members is a struct. Classes have been implemented in C++ as structs.

True, all true but the OP wanted to implement (part of) the shebang in C only,
no C++.

kind regards,

Jos