How to pass or return a structure to/from a Function in C/C++?

A structure is a user-defined data type in C/C++. A structure creates a data type that can be used to group items of possibly different types into a single type.

How to pass structure as an argument to the functions?

Passing of structure to the function can be done in two ways:

• By passing all the elements to the function individually.
• By passing the entire structure to the function.

In this article, entire structure is passed to the function. This can be done using call by reference as well as call by value method.

Examples 1: Using Call By Value Method

// C++ program to pass structure as an argument
// to the functions using Call By Value Method

#include <bits/stdc++.h>
using namespace std;

struct Distance {
    int kilometer;
    int meter;
};

// accepts distance as its parameters
void TotalDistance(Distance d1, Distance d2)
{
    // creating a new instance of the structure
    Distance d;

    // assigning value to new instance of structure
    d.kilometer = d1.kilometer
                  + d2.kilometer
                  + (d1.meter + d2.meter)
                        / 1000;

    d.meter = (d1.meter + d2.meter) % 1000;

    cout << "Total distance:";
    cout << "kilometer: "
         << d.kilometer << endl;

    cout << "meter: " << d.meter
         << endl;
}

// Function that initialises the value
// and calls TotalDistance function
void initializeFunction()
{
    // creating two instances of Distance
    Distance Distance1, Distance2;

    // assigning values to structure elements
    Distance1.kilometer = 10;
    Distance1.meter = 455;

    Distance2.kilometer = 9;
    Distance2.meter = 745;

    // calling function with (structure)
    // distance as parameters
    TotalDistance(Distance1, Distance2);
}

// Driver code0
int main()
{

    // Calling function to do required task
    initializeFunction();

    return 0;
}

Output:

Total distance:kilometer: 20
meter: 200

Examples 2: Using Call By Reference Method

// C++ program to pass structure as an argument
// to the functions using Call By Reference Method

#include <bits/stdc++.h>
using namespace std;

struct number {
    int n;
};

// Accepts structure as an argument
// using call by reference method
void increment(number& n2)
{
    n2.n++;
}

void initializeFunction()
{
    number n1;

    // assigning value to n
    n1.n = 10;

    cout << " number before calling "
         << "increment function:"
         << n1.n << endl;

    // calling increment function
    increment(n1);

    cout << "number after calling"
         << " increment function:" << n1.n;
}

// Driver code
int main()
{
    // Calling function to do required task
    initializeFunction();

    return 0;
}

Output:

number before calling increment function:10
number after calling increment function:11

How to return a structure from the functions?

To return a structure from a function the return type should be a structure only.

Examples:

// C++ program to return a structure from
// a function using Call By Value Method

#include <iostream>
#include <stdlib.h>

using namespace std;

// required structure
struct Employee {
    int Id;
    string Name;
};

// return type of the function is structure
Employee data(Employee E)
{

    // Assigning the values to elements
    E.Id = 45;
    E.Name = "aman";

    // returning structure
    return (E);
}

// Driver code
int main()
{

    // creating object of Employee
    Employee Emp;

    // calling function data to assign value
    Emp = data(Emp);

    // display the output
    cout << "Employee Id: " << Emp.Id;
    cout << "\nEmployee Name: " << Emp.Name;

    return 0;
}

Output:

Employee Id: 45
Employee Name: aman