How Can a C/C Function Return a Modified Array?

Returning Arrays in Functions

Arrays are fundamental data structures used to store collections of similar data items. In C and C , arrays are passed to functions as pointers to the first element of the array. Understanding how to return arrays from functions is crucial for efficiently managing data in programs.

Question:

Consider the following function declaration:

int fillarr(int arr[]);

How can the function fillarr return the modified array arr to the calling function?

Answer:

1. Returning an Array Pointer (Address):

Although arrays are not inherently pointers, they can be implicitly treated as pointers to the first element. By using the array variable arr as a function parameter, the function actually receives a pointer to the first element. To return the modified array, the function should return a pointer of type int* pointing to that element:

int* fillarr(int arr[])
{
    // Modifications to the array elements...
    return arr;
}

This approach allows the calling function to use the returned pointer as an array reference:

int main()
{
    int y[10];
    int *a = fillarr(y); // a now points to the first element of y
}

2. Accessing the Returned Array:

Once the function returns a pointer to the array, the calling function can access the array elements using pointer arithmetic:

// Accessing the first element of the modified array
int element1 = a[0];

It's important to note that returning the pointer to the local array in the function is a common mistake. The local array is destroyed once the function exits, making the returned pointer invalid. Therefore, it's crucial to pass an array from the calling function and return only a pointer to the first element.

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