Deletion Using memcpy in an array

Question

Given an index and an array of integers, I need to delete the element in the given array which was stored in the given index through the use of memcpy(). The new set of elements will be stored on the given array.

Here's an illustration of what I want to do, though I'm having trouble implementing it.

So arrayElem after deleting 10 would look like this:

Answer 1

You can't use memcpy, because source and destination overlap, but you can use memmove, e.g.:

memmove(&a[1], &a[2], 5 * sizeof(a[0]));

This copies the 5 elements starting at a[2] down to the 5 elements starting at a[1], taking care of the fact that the source and destination regions overlap.

Answer 2

You may not use function memcpy because the ranges of the array overlap each other. In this case the behaviour will be undefined.

Instead you have to use standard function memmove.

Here is a demonstrative program

#include <stdio.h>
#include <string.h>

size_t remove_by_index( int a[], size_t n, size_t i )
{
    if ( i < n )
    {
        memmove( a + i, a + i + 1, ( n - i - 1 ) * sizeof( *a ) );
        --n;
    }

    return n;
}

int main( void ) 
{
    int a[] = { 1, 10, 5, 8, 4, 51, 2 };
    const size_t N = sizeof( a ) / sizeof( *a );
    size_t n = N;

    for ( size_t i = 0; i < n; i++ ) printf( "%d ", a[i] );
    printf( "\n" );

    n = remove_by_index( a, n, 1 );

    for ( size_t i = 0; i < n; i++ ) printf( "%d ", a[i] );
    printf( "\n" );

    return 0;
}

The program output is

1 10 5 8 4 51 2 
1 5 8 4 51 2