Using a struct to pass multiple values

Question

So I have a function that requires two characters and two ints:

void need_2xcha_2xint(char a, char b, int x, int y)
{
  cout << "Working! a: " << a << ", b: " << b << ", x : " << x << ", y: " << y << ".\n";
}

I would like to call it by passing a single struct that contains the four values:

struct Value_Holder
{
char a;
char b;
int x;
int y;

Value_Holder()
    : a('g'), b('h'), x(3), y(5)
  {
  }
};

I want to be able to call it as follows :

Value_Holder vh;
need_2xcha_2xint(vh);

Of course I could write another function that accepts my custom structure and deals with it appropriate, but I was wondering if there's a way to tell the struct to output four seperate values directly. This will mainly be used for interacting with DirectX libraries.

I'm sure this is basic stuff, but I've been working on so many different areas of c++ it's hard to remember everything. I've searched for the answer for a while now, but I'm not quite sure what I should be searching for. My google skills fail me!

Thanks in advance.

• EDIT -

As it seems people are confused by my qustions I'll try and simplify it here:

Is there a way for a function that requires 2 ints and 2 chars to accept a single structure holding these values instead of four seperate values?

I hope that clarifies my question.

Answer 1

Wrap the third party library:

namespace david {

void need_2xcha_2xint(const Value_Holder& value) {
    ::need_2xcha_2xint(value.a, value.b, value.x, value.y);
}

}

Using it:

int main() {
    Value_Holder value;

    using david::need_2xcha_2xint;
    need_2xcha_2xint(value);
    return 0;
}

edit

I'm pretty sure you could encapsulate this using templates and function pointers.

Answer 2

a way to tell the struct to output four seperate values directly

If you mean output as in to a std::ostream (e.g. std::cout), then add a streaming operator for Value_Holder...

std::ostream& operator<<(std::ostream& os, const Value_Holder& v)
{
    return os << "{ a " << v.a << ", b " << b.b << ", x " << x << ", y " << y << " }";
}

Then you can print it succinctly using e.g.:

Value_Holder v;
...
std::cout << "whatever " << v << " some more\n";

Answer 3

I think the answer provided by fuchsgeist is the best way to do it. If I am to understand correct then you need to pass 4 params to your library function. I hope below code solved your problem.

Value_Holder vh;
need_2xcha_2xint(vh.a,vh.b,vh.x,vh.y);

I Hope I understood your problem correctly.

Ok I got your question after your Edit. You can use function overloading concept here. Overload the library function to accept your structure.Will that be a solution to your problem?

Answer 4

I know that this is not very good decision, and you should avoid any defines, but anyway, you can try this:

void f(int i, char c)
{
    std::cout << i << " : " << c;
}

struct s
{
    int i;
    char c;
};

#define S_CALL(f, s) (f(s.i, s.c))

int main(int argc, char* argv[])
{
    s param;
    param.i = 1;
    param.c = 'a';

    f(param.i, param.c);
    S_CALL(f, param);

    return 0;
}

Of course it's not far from wrapping this function in your own.

Answer 5

Is there a way for a function that requires 2 ints and 2 chars to accept a single structure holding these values instead of four seperate values?

No, there isn't.

You could try different tricks with preprocessor, but it's a wrong and dead end way.

Why don't you just use the structure? Follow the KISS principle as often as you can.

Answer 6

The needing to pass several parameters to a function leads to the conclusion that a subjacent object is needed. In your case you created your struct.

But don't forget the Single Responsibility Principle, which requires to think about the responsibilities of your classes: a classes should remain simple and clear, and not just a mess of sometimes unrelated parameters.

In your case, I'm am not sure, but when ever I see (int x, int y), I wonder if a class Point or Vector, or class Size is at stake. If so I would encapsulate only the pair int x, int y in the new class in question.

For such questions, I recommend the Book "Refactoring: Improving the Design of Existing Code" by Martin Fowler. He list the ways to modify, the code into a cleaner more maintainable, modifiable sate, and when/why to refactor the code.