Passing structs to a void function

Question

My question is how do you pass a struct.variable (or the struct array) to the void function. Basically the code looks as follows:

Structs

struct Person{
    string surname;
    string BType;
    string organ;
    int age;
    int year, ID, IDp;
} Patient[50], Donor[50];

int i; // counter variables for the arrays such as Patient[i].BType... etc
int i1; 

Then the code for the function is a line like this:

void compare(int &i, int &i1, Person &Patient[50], Person &Donor[50]);

I tried to pass the i , i1 , Patient and Donor structs. Why won't this work? Is there a special way to pass these sorts of structs to a function?

The values into the variable structs also are read from a file (don't think that changes anything here). Any ideas?

Answer 1

Your function prototype is incorrect. To pass a fixed array type reference, you must qualify the reference part of the parameter outside the array index declaration.

void compare(int &i, int &i1, Person (&Patient)[50], Person (&Donor)[50])
//  note parens ----------------------^-------^-------------^------^

Invoke as simply

compare(i, i1, Patient, Donor);

It is interesting to note you can do this with a template that guarantees the fixed-array size via deduction.

template<size_t N>
void compare(int &i, int &i1, Person (&Patient)[N], Person (&Donor)[N])
{
    // N is guarenteed to be the size of your array. You can use it
    //  as you would 50 in your code.
    for (size_t i=0; i<N;++i)
    {
        // do something with Patient and Donor elements
    }
}

This has the added benefit of allowing instantiating with different array sizes. Ie You can also do this:

Person Patient[50], Donor[50];
Person MorePatients[10], MoreDonors[10];

....

compare(i, i1, Patient, Donor);
compare(i, i1, MorePatients, MoreDonors)

and it will compile correctly. I suggest you experiment with it, you may find it useful.

Answer 2

In addition to what WhozCraig has said, you could even put variadic template parameters in there to allow passing any number of types of things you can find in a hospital, such as nurses and midwives!

template <typename T1, size_t N1>
void compare(int &i, int &i1, T1 (&array)[N1]) {
    for (const auto& elem : array) {
        std::cout << elem.name << std::endl;   
    }
}

template <typename T1, size_t N1, typename... Ts, size_t... Ns>
void compare(int &i, int &i1, T1 (&array)[N1], Ts (&... arrays)[Ns]) {
    for (const auto& elem : array) {
        std::cout << elem.name << std::endl;   
    } 
    std::cout << std::endl;
    compare(i, i1, arrays...);
}

struct Nurse
{ std::string name; };

struct Midwife
{ std::string name; };


int main() {
    Nurse nurses[] = {{"Nina"}, {"Austin"}};
    Midwife midwives[] = {{"Matriona"}, {"Lizbeth"}, {"Jill"}};
    Nurse evenMoreNurses[] = {{"Maria"}, {"Nick"}, {"Martine"}, {"Ashley"}};

    int i{};
    int i1{};

    compare(i, i1, nurses, midwives, evenMoreNurses);
}

Do you realize now just how fun C++ can be?

Answer 3

just declare function like this:

void compare(int i, int i1, Person *Patient, Person *Donor);

you can invoke like:

compare(i, i1, Patient, Donor)