Difference between sizeof(int *) and sizeof(int) in C/C++

sizeof() is commonly used operator in the C or C++. It is a compile-time unary operator that can be used to compute the size of its operand. The result of sizeof() is of unsigned integral type which is usually denoted by size_t. This operator can be applied to any data-type, including primitive types such as integer and floating-point types, pointer types, or compound datatypes such as structure, union etc.

int means a variable whose datatype is integer.
sizeof(int) returns the number of bytes used to store an integer.

int* means a pointer to a variable whose datatype is integer.
sizeof(int*) returns the number of bytes used to store a pointer.

Since the sizeof operator returns the size of the datatype or the parameter we pass to it. So, the value it should return after passing a variable of (int *) to it:

• Since int* points to an address location as it is a pointer to a variable, So, the sizeof(int*) simply implies the value of the memory location on the machine, and, memory Locations themselves are 4-byte to 8-byte integer values.
• On a 32-bit Machine, sizeof(int*) will return a value 4 because the address value of memory location on a 32-bit machine is 4-byte integers.
• Similarly, on a 64-bit machine it will return a value of 8 as on a 64-bit machine the address of a memory location are 8-byte integers.

Now, the value it should return after passing a variable of (int) to it:

• Since int in an integer type variable. So, the sizeof(int) simply implies the value of size of an integer.
• Whether it is a 32-bit Machine or 64-bit machine, sizeof(int) will always return a value 4 as the size of an integer.

Below is the illustration of sizeof operator on 64-bit machine:

C

// C program to illustrate the
// sizeof operator
#include <stdio.h>

// Driver code
int main()
{
    // Print the sizeof integer
    printf("Size of (int) = %lu"
           " bytes\n",
           sizeof(int));

    // Print the size of (int*)
    printf("Size of (int*) = %lu"
           " bytes\n",
           sizeof(int*));

    return 0;
}

C++

// C program to illustrate the
// sizeof operator
#include "bits/stdc++.h"
using namespace std;

// Driver Code
int main()
{
    // Print the sizeof integer
    cout << "Size of (int) = "
         << sizeof(int) << " bytes\n";

    // Print the size of (int*)
    cout << "Size of (int *) = "
         << sizeof(int*) << " bytes\n";

    return 0;
}

Output:

Size of (int) = 4 bytes
Size of (int*) = 8 bytes