Do Not Use sizeof For Array Parameters in C

Why Does C Treat Array Parameters as Pointers?

Last Updated : 12 Apr, 2023

In C, array parameters are treated as pointers mainly to,

To increase the efficiency of code
To save time

It is inefficient to copy the array data in terms of both memory and time; and most of the time, when we pass an array our intention is to just refer to the array we are interested in, not to create a copy of the array.

The following two definitions of fun() look different, but to the compiler, they mean exactly the same thing.

void fun(int arr[]) { 
    // body
}
// This is valid


void fun(int *arr) { 
    // body
}
// This is valid too

It’s preferable to use whichever syntax is more accurate for readability.

Note: If the pointer coming in really is the base address of a whole array, then we should use [ ].

Example: In this example, the array parameters are being used as pointers.

C

// C Program to demonstrate that C treats array parameters
// as pointers
#include <stdio.h>
 
void findSum1(int arr[])
{
    int sum = 0;
    for (int i = 0; i < 5; i++)
        sum = sum + arr[i];
    printf("The sum of the array is: %d\n", sum);
}
 
void findSum2(int* arr)
{
    int sum = 0;
    for (int i = 0; i < 5; i++)
        sum = sum + arr[i];
    printf("\nThe sum of the array is: %d \n", sum);
}
 
// Driver code
int main()
{
    int arr[5] = { 1, 2, 3, 4, 5 };
 
    findSum1(arr);
    findSum2(arr);
    return 0;
}

C++

// C++ Program to demonstrate that C treats array parameters
// as pointers
#include <iostream>
using namespace std;
 
void findSum1(int arr[])
{
    int sum = 0;
    for (int i = 0; i < 5; i++)
        sum = sum + arr[i];
    cout <<"The sum of the array is: " << sum;
}
 
void findSum2(int* arr)
{
    int sum = 0;
    for (int i = 0; i < 5; i++)
        sum = sum + arr[i];
    cout <<"\nThe sum of the array is: "<< sum;
}
 
// Driver code
int main()
{
    int arr[5] = { 1, 2, 3, 4, 5 };
 
    findSum1(arr);
    findSum2(arr);
    return 0;
}
 
// this code is contributed by shivanisinghss2110

Output

The sum of the array is: 15

The sum of the array is: 15

Do Not Use sizeof For Array Parameters in C

kartik

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