Structures in C/C++: Defining and Using Structures

Introduction to Structures in C/C++

In procedural and object-oriented programming alike, there’s often a need to group different types of variables under a single name. This is where Structures in C/C++ come in.

Introduced as a way to handle complex data, structures form the foundation for advanced programming concepts like classes and objects in C++. This detailed blog from Kamlesh Singad at Code With Kamlesh dives deep into the definition, usage, and practical implementation of structures.

Importance of Structures in Programming

Think of a student record. It includes:

• Roll number (int)
• Name (string)
• Marks (float)

Instead of declaring separate variables for each student, you can group them into one logical unit: a structure.

Benefits include:

• Code readability
• Data organization
• Ease of maintenance

Also Read: Pointer Arithmetic & Pointer Arrays in C/C++

Declaring a Structure in C

struct Student {
    int roll;
    char name[50];
    float marks;
};

Here, Student is a user-defined data type.

Initializing Structure Variables

struct Student s1 = {1, "Amit", 92.5};

You can also assign values member-by-member:

s1.roll = 2;
strcpy(s1.name, "Neha");
s1.marks = 88.75;

Structure Syntax in C++

C++ maintains backward compatibility with C:

struct Book {
    string title;
    int pages;
};

Additionally, C++ allows functions inside structs, and access specifiers like public, private.

Also Read: Pointers in C/C++: Basics and Advanced Concepts – Complete Guide

Nesting Structures

Structures can contain other structures:

struct Date {
    int day, month, year;
};

struct Student {
    int roll;
    struct Date dob;
};

Array of Structures

struct Student students[3];

Useful when handling multiple records.

Accessing Members

Use the dot operator:

printf("%s", s1.name);

For pointers:

struct Student *ptr = &s1;
printf("%d", ptr->roll);

Passing Structures to Functions

By value:

void display(struct Student s) { ... }

By reference (efficient):

void update(struct Student *s) { s->marks += 5; }

Returning Structures from Functions

struct Student createStudent() {
    struct Student s = {101, "Ravi", 91.0};
    return s;
}

typedef with Structures

To simplify:

typedef struct Student {
    int roll;
    char name[50];
} Student;

Now use:

Student s1;

File Handling with Structures

FILE *fp = fopen("students.dat", "wb");
fwrite(&s1, sizeof(s1), 1, fp);
fclose(fp);

Real-Life Example: Student Management System

Create an array, write to file, sort and display students using:

• Structures
• File I/O
• Functions

Also Read: Arrays in C/C++: Single & Multi-dimensional

Dynamic Memory Allocation

Student *s = (Student *)malloc(sizeof(Student));

In C++:

Student *s = new Student;

Memory Layout and Padding

Use sizeof(struct Student) to analyze memory. Padding may cause sizes to differ based on compiler alignment rules.

Structures vs Classes

Feature	Structure	Class
Default access	public	private
Supports functions	Yes	Yes
Inheritance	No (C++)	Yes (C++)

Combining Strings and Structures

char name[50]; // in C

In C++:

string name;

Use getline(cin, s.name) to read full name.

Structure Array Sorting

sort(students, students+n, [](Student a, Student b) {
    return a.marks > b.marks;
});

Searching in Structure Array

for (int i = 0; i < n; i++) {
    if (students[i].roll == target)
        return i;
}

Use in Game Development

Example:

struct Player {
    string name;
    int level;
    int health;
};

Best Practices

• Initialize all members
• Use typedef for clarity
• Prefer string in C++ over char[]

Common Mistakes

• Forgetting to include #include <string.h>
• Mixing C and C++ syntax
• Not using pointers when passing large structs

FAQs

What is a structure in C/C++?
A structure groups variables of different data types under one name.

Can I have functions in a structure?
Yes, in C++, not in C.

What is the default access modifier for struct in C++?
public

Can a structure have another structure inside it?
Yes, that’s called a nested structure.

How do you access structure members using a pointer?
Use the arrow operator ->

Can I return a structure from a function?
Yes, C and C++ both allow returning structs.

Conclusion

Structures are powerful and form the backbone of modular design in both C and C++. Understanding them bridges your knowledge toward Object-Oriented Programming. This blog by Kamlesh Singad, curated under Code With Kamlesh, aims to build your skills with easy, real-world examples.

Continue your journey into OOP and classes in the next blog!