Should I use structs in C++?

Question

The difference between struct and class is small in C++, basically only that struct members are per default public and class members are per default private.

However, I still use structs whenever I need pure data structures, for instance:

struct Rectangle {
    int width;
    int height;
};

I find that very convenient to work with:

Rectangle r;
r.width = 20;
r.height = 10;

However, data structures are from procedural programming, and I'm doing object oriented programming. Is it a bad idea to introduce this concept into OO?

Answer 1

No. If it makes sense to use a struct somewhere, why would you complicate things using something else that isn't meant to fit the purpose ?

In my projects, I tend to use struct for simple "structures" which just need to hold some trivial data.

If a data structure needs to have some "smartness" and hidden fields/methods, then it becomes a class.

Answer 2

In my opinion, no, this is not a bad idea. If you're going to use a class in the same fashion, like

class Rectangle {
    public:
        int width;
        int height;
};

then you may as well use a struct. This will help make sure you're not forgetting to declare anything public, and if you keep it consistent, then future developers (including future you) will know that you intended this purely as a data object, not something to have methods within.

It's still pretty much an object from all usability perspectives, so no, it doesn't conflict with OO design.

Answer 3

If your application needs it, use it. If your design requires you to have just public members you can use struct itself...

Answer 4

I use structs all the time for objects like unary_function and such. There's really no point in having to explicitly declare public on a class with only an operator() method. Furthermore, it's not like you're inviting it to be inherited.

Answer 5

I would prefer struct-like class. The first reason is to avoid uninitialized struct. The other reason is that you will be always able to add any convenience methods to the struct if wanted.

Answer 6

structs are especially useful for POD (plain old data) encapsulation. There is a lot more on this at struct vs class in C++

Answer 7

Sometimes using classes with constructors will be less performance efficient than using structs, particularly when copying large amounts of data around arrays. The reason being you can safely use functions such as memcpy to move large blocks of data around the place, whereas with a class your more likely to use an iterator and/or copy construtor.

See a previous question of mine for some further discussion on this.

Answer 8

It sounds like, you own a Ferrari Scaglietti and a Lamborgini Espada, sometime you drive Ferarri, sometime you drive Lamborghini.... Sometime you use struct, sometime you use class, is there any true and false?

Answer 9

I used to do the following:

struct Interface
{
    virtual ~Interface() {}
    virtual void foo() = 0;
};

class Implementation : public Interface
{
    void foo(); // or public, it depends.
public:
    Implementation(...);
};

since by default, interface have all their members public, and by default, implementations have their members private.

Answer 10

There is nothing wrong with using a struct in C++, I tend to avoid using classes unless I have ample time to plan out what their purpose should be.