Copying one array into another using pointers and array indexing

Question

I've written a program that copies one array into another using array indexing and pointers. The problem I'm trying to solve is when I go to print the original array and the new array for the pointer method I get the same thing(i.e the copied array) when what I really want is the original array printed and then the new copied array. (much clearer below)

CODE

/* 
Program to copy the contents of a one-dimensional character array 
into another one-dimensional character array using
2 different methods(Pointers and Array Indexing)
*/

#include <stdio.h>
// Declaring both functions
void copyArrayIndexWay(char * const newArray1, const char * const originalArray1);
void copyPointerWay(char *newArray2, const char *originalArray2);

// Little explanation - I declared both arrays here instead of in my main so that my variable size can get the size of
// either array which is used in the for loops for both functions. Hence why I had to delcare it all here if I
// wanted both functions to be able to access the size variable
char array1[] = "deeznuts";
char array2[] = "gotem";

// Declaring variables i and size here which will allow both functions to call them
int size = sizeof(array1), i = 0;

int main(){

    // copy 1 into 2
    copyArrayIndexWay(array2, array1);
    copyPointerWay(array2, array1);

}

// Functin to copy contents using array indexing
void copyArrayIndexWay(char * const newArray, const char * const originalArray){
    
    printf("--Copying Using Array Indexing--\n");
    printf("Original Array: %s\n", newArray);

    for (i=0; i<size; i++){
        newArray[i] = originalArray[i];
    }

    printf("New Array: %s\n\n\n", newArray);


}

// Function to copy contents using pointers
void copyPointerWay(char *newArray2, const char *originalArray2){
    
    // declare pointers and assign both arrays to a pointer each
    const char *orig_arrayPtr;
    orig_arrayPtr = originalArray2; // array1

    char *new_arrayPtr;
    new_arrayPtr = newArray2; // array2

    printf("--Copying Using Pointers--\n");
    printf("Original Array: %s\n", new_arrayPtr);

    for (i=0; i<size; i++){
        new_arrayPtr[i] = orig_arrayPtr[i];
    }

    printf("New Array: %s\n", new_arrayPtr);

}

OUTPUT

--Copying Using Array Indexing--
Original Array: gotem
New Array: deeznuts


--Copying Using Pointers--
Original Array: deeznuts
New Array: deeznuts

The copying using pointers should print the same original array as the array indexing method but for some reason it prints the new array instead. Any advice or explanation on why this is happening would be much appreciated, thanks :)

anotherOne · Accepted Answer · 2021-02-21 00:33:03Z

1

After calling

 copyArrayIndexWay(array2, array1);

array2 and array1 have the same content (deeznuts). So then in the call

copyPointerWay(array2, array1);

you are passing "deeznuts" two times.

Actually you are invoking undefined behaviour by accessing array2 out of bounds, because it is shorter than "deeznuts". But you are lucky to not access memory you should not access.

You could solve the problem in many ways, my suggestion is to pass only the original array that you want to copy (deeznuts) and then in each function declare an array large enough to contain the one you are passing.

edited Feb 21, 2021 at 0:33

answered Feb 21, 2021 at 0:15

anotherOne

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1 Comment

Horizon Over a year ago

Hi, thanks for the advice. I re-worked my code slightly and implemented the suggestion you gave and I no longer have this issue anymore, much appreciated :)

tstanisl · Accepted Answer · 2021-02-21 00:18:56Z

1

Array2 is already filled with "deeznuts" when copyPointerWay is called.

answered Feb 21, 2021 at 0:18

tstanisl

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Comments

Zois Tasoulas · Accepted Answer · 2021-02-21 00:20:32Z

1

The behavior you observe is explained because:

Initially array2 contains "gotem"

After calling copyArrayIndexWay, array2 contains "deeznuts"

When calling copyPointerWay, array2 contains "deeznuts" and "deeznuts" is again written in this location. That's why you cannot observe a change in the content.

You could assign another value to array2, after calling copyArrayIndexWay. That way you will observe difference in the contents.

answered Feb 21, 2021 at 0:20

Zois Tasoulas

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