A structure is a collection of variables of different data types and member functions under a single name.
It is similar to a class as both hold a collection of data of different data types.
Suppose you want to store some information about a person: their first_name, last_name, age, and salary.
You can easily create different variables—first_name, last_name, age, salary—to store this information separately.
However, in the future, you might want to store information about multiple people.
Now, you'd need to create different variables for each information per person: first_name1, last_name1, age1, salary1, first_name2, last_name2, age2, salary2, …
You can visualize how big and messy the code would look. Additionally, as there is no relation between the variables (information), it would be a daunting task to manage.
A better approach is to have a collection of all related information under a single name, such as Person and use it for every individual.
Now, the code looks much cleaner, more readable, and efficient as well.
This collection of all related information under a single name Person is a structure.
How to Declare a Structure in C++ Programming?
The struct keyword defines a structure type followed by an identifier (name of the structure).
Then, inside the curly braces, you can declare one or more members (declare variables inside curly braces) of that structure. For example:
struct Person
{
string first_name;
string last_name;
int age;
float salary;
};
Here, the structure Person is defined which has four members: first_name, last_name, age, and salary.
When a structure is defined, no memory is allocated.
The structure definition is only the blueprint for the creation of variables. You can imagine it as a data type.
When you define an integer as below:
int foo;
The int specifies that variable foo can hold integer elements only. Similarly, structure definition only specifies what property a structure variable holds when it is defined.
Note: Remember to end the declaration with a semicolon (;).
How to Define a Structure Variable?
Once you declare a structure Person as above, you can define a structure variable as:
Person bill;
Here, a structure variable bill is defined, which is of type structure Person.
Only when the structure variable is declared is the required memory allocated by the compiler.
How to Access Members of a Structure?
The members of a structure variable are accessed using a dot (.) operator.
Suppose you want to access the age of the structure variable bill and assign 50 to it. You can perform this task by using the following code:
bill.age = 50;
Example: C++ Structure
// Program to assign data to members of a structure variable
#include <iostream>
using namespace std;
struct Person
{
string first_name;
string last_name;
int age;
float salary;
};
int main()
{
Person p1;
cout << "Enter first name: ";
cin >> p1.first_name;
cout << "Enter last name: ";
cin >> p1.last_name;
cout << "Enter age: ";
cin >> p1.age;
cout << "Enter salary: ";
cin >> p1.salary;
cout << "\nDisplaying Information." << endl;
cout << "First Name: " << p1.first_name << endl;
cout << "Last Name: " << p1.last_name << endl;
cout << "Age: " << p1.age << endl;
cout << "Salary: " << p1.salary;
return 0;
}
Output
Enter first name: Jane Enter last name: Smith Enter age: 27 Enter salary: 10000 Displaying Information. First Name: Jane Last Name: Smith Age: 27 Salary: 10000
Here the structure Person is declared which has four members: first_name, last_name, age and salary.
Inside the main() function, a structure variable p1 is defined. Then, the user is asked to enter information, and data entered by the user is displayed.
Member Functions in C++ Structures
In C++, structures can also have member functions.
These member functions are similar to regular functions but are defined within the scope of a structure. They can access and manipulate the data members of the structure directly.
We can declare a member function by defining the function within the structure definition.
struct Person {
string first_name;
string last_name;
int age;
float salary;
// member function to display information about the person
void displayInfo() {
cout << "First Name: " << first_name << endl;
cout << "Last Name: " << last_name << endl;
cout << "Age: " << age << endl;
cout << "Salary: " << salary << endl;
}
};
In this example, the Person structure includes a member function, displayInfo() which displays the information about the person.
Let's look at an example.
#include <iostream>
using namespace std;
struct Person {
string first_name;
string last_name;
int age;
float salary;
// member function to display information about the person
void display_info() {
cout << "First Name: " << first_name << endl;
cout << "Last Name: " << last_name << endl;
cout << "Age: " << age << endl;
cout << "Salary: " << salary << endl;
}
};
int main() {
Person p1;
cout << "Enter first name: ";
cin >> p1.first_name;
cout << "Enter last name: ";
cin >> p1.last_name;
cout << "Enter age: ";
cin >> p1.age;
cout << "Enter salary: ";
cin >> p1.salary;
// display information using member function
cout << "\nDisplaying Information." << endl;
p1.display_info();
return 0;
}
Output
Enter first name: Jane Enter last name: Smith Enter age: 27 Enter salary: 10000 Displaying Information. First Name: Jane Last Name: Smith Age: 27 Salary: 10000
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