Availability of private and protected in C++ structs

Question

Can we use access specifiers - private and protected - in C++ structs (as opposed to classes)?

Also, do access modifiers exist in C?

Answer 1

C doesn't have C++style access modifiers. A C struct is just a composite object type containing members of other object types.

In C++, a struct and a class are almost identical; the only difference is that struct members are public by default, and class members are private by default. So this:

struct foo {
private:
    // ...
};

is equivalent to this:

class foo: {
    // ...
};

This has been answered elsewhere.

This implies that the private, public, and protected keywords are equally valid in either a struct definition or a class definition.

As a matter of programming style, on the other hand, if you're going to be using access modifiers, it's probably best to define your type as a class rather than as a struct. Opinions will differ on this, but IMHO the struct keyword should be used for POD (Plain Old Data) types, or for types that could be defined as structs in C.

C++ structs, strictly speaking, are very different from C structs, and are nearly identical to C++ classes. But if I see something defined in C++ as a struct, I expect (or at least prefer) it to be something similar to a C struct.

Answer 2

In C++ a structure is the same as class with the only difference that the default scope is public unlike private that is the default scope for class. In C access specifiers don't exist but after all what would you use them for?