Initializing C Structures in C ++

Question

I am creating a bunch of C structures, so I can encapsulate the data passed through the dll c interface. Structures have many members, and I want them to have default values, so that they can be created with only a few members.

As I understand it, structures should remain c-style, so they cannot contain constructors. What is the best way to create them? I was thinking about a factory?

Answer 1

struct Foo { static Foo make_default (); }; 

A factory is redundant. You use it when you want to create instances of this interface, but the type of execution execution is not statically known at the place of creation.

Answer 2

C Structures may still have member functions. However, problems will arise if you start using virtual functions, since this requires a virtual table somewhere in the structure's memory. Normal member functions (such as a constructor) do not actually add any size to the structure. You can pass structure to DLL without problems.

Answer 3

I would use the constructor class:

 struct Foo { ... }; class MakeFoo { Foo x; public: MakeFoo(<Required-Members>) { <Initalize Required Members in x> <Initalize Members with default values in x> } MakeFoo& optionalMember1(T v) { x.optionalMember1 = v; } // .. for the rest option members; operator Foo() const { return x; } }; 

This allows arbitrary sets of structure elements in the expression:

 processFoo(MakeFoo(1,2,3).optionalMember3(5)); 

Answer 4

I have an easy idea, here's how:

Create the structure as usual and create a simple function that initializes it:

 struct Foo{...}; void Default(Foo &obj) { // ... do the initialization here } 

If you have several structures, in C ++ you are allowed to overload the function, so you can have many functions called "default", each of which initializes its own type, for example:

 struct Foo { //... }; struct Bar { //... }; void Default(Foo &obj) {...} void Default(Bar &obj) {...} 

The C ++ compiler will know when to call the first or second overload based on this parameter. It makes a reference to any parameter that you give it, so any changes made to obj will be reflected in the variable that you put as the parameter.

Edit: I also have an idea how to specify some parameters, you can do this using the default parameters. Here's how it works:

For example, you use the following function; You can specify default values ​​for such parameters:

 void Default (Foo &obj, int number_of_something = 0, int some_other_param = 10) { ... }