C++ `sizeof` Operator

Learn how the sizeof operator works in C++ with easy examples. Understand how to find the size of variables and data types in bytes for memory management and C++ programming.

1. What is the sizeof Operator?

The sizeof operator is used to find the size of a data type or variable in bytes.

Syntax

sizeof(variable)

or

sizeof(data_type)

The result of sizeof is given in bytes.

2. Example: sizeof with Data Types

#include <iostream>
using namespace std;

int main() {
    cout << sizeof(int) << endl;
    cout << sizeof(float) << endl;
    cout << sizeof(double) << endl;
    cout << sizeof(char) << endl;

    return 0;
}

Possible Output:

4
4
8
1

Note: The size of some data types can vary depending on the compiler and computer system. char is always 1 byte.

3. Example: sizeof with Variables

#include <iostream>
using namespace std;

int main() {
    int age = 20;
    double salary = 50000.5;
    char grade = 'A';

    cout << sizeof(age) << endl;
    cout << sizeof(salary) << endl;
    cout << sizeof(grade) << endl;

    return 0;
}

Possible Output:

4
8
1

Understand the Code

• sizeof(age) → finds the size of the int variable.
• sizeof(salary) → finds the size of the double variable.
• sizeof(grade) → finds the size of the char variable.

4. sizeof Does Not Give the Value

Consider:

int age = 20;

cout << age << endl;
cout << sizeof(age) << endl;

Output:

20
4

Here:

• age gives the value → 20
• sizeof(age) gives the memory size → 4 bytes on a typical system.

5. sizeof with Arrays

sizeof can also be used with arrays.

#include <iostream>
using namespace std;

int main() {
    int numbers[5];

    cout << sizeof(numbers);

    return 0;
}

If an int is 4 bytes:

5 × 4 = 20 bytes

Output:

20

6. Finding the Number of Elements in an Array

We can use sizeof to find the number of elements in an array:

int numbers[5];

int total = sizeof(numbers) / sizeof(numbers[0]);

cout << total;

Output:

5

Why?

sizeof(numbers)     = 20 bytes
sizeof(numbers[0])  = 4 bytes

20 / 4 = 5

Therefore, the array contains 5 elements.

⭐ Quick Revision

Remember

sizeof tells us how many bytes are occupied by a data type, variable, or object.

Important: sizeof returns a size in bytes, not bits.