Select certain elements in array to create new array

Question

How could I select a certain number of elements from an array by giving a start and ending index number to create a new array?

For example, if my original array was {1,2,3,4,5,6}, and I say x=0 and y=2 for their index values, I would have a new array that is {1,2,3}.

Thank you.

Answer 1

If your compiler supports variable length arrays then you can do this the following way

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

int main(void) 
{
    int a[] = { 1, 2, 3, 4, 5, 6 };
    size_t n1 = 0, n2 = 2;
    int b[n2 - n1 + 1];

    memcpy( b, a + n1, ( n2 - n1 + 1 ) * sizeof( int ) );

    size_t n = sizeof( b ) / sizeof( *b );

    for ( size_t i = 0; i < n; i++ )
    {
        printf( "%d ", b[i] );
    }

    putchar( '\n' );

    return 0;
}

The program output is

1 2 3

Otherwise the new array should be allocated dynamically as for example

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

int main(void) 
{
    int a[] = { 1, 2, 3, 4, 5, 6 };
    size_t n1 = 0, n2 = 2;

    size_t n = n2 - n1 + 1;
    int *b = malloc( n * sizeof( *b ) );

    memcpy( b, a + n1, n * sizeof( int ) );

    for ( size_t i = 0; i < n; i++ )
    {
        printf( "%d ", b[i] );
    }

    putchar( '\n' );

    free( b );

    return 0;
}