Editing Stride of an array (section)

==Reasons for non-unit stride==
Arrays may have a stride larger than their elements' width in bytes in at least two cases:

===Overlapping parallel arrays===
Some languages allow [[AoS_and_SoA#Array of structures|arrays of structures]] to be treated as overlapping [[parallel array]]s with non-unit stride:

<syntaxhighlight lang="c">
#include <stdio.h>

struct MyRecord {
    int value;
    char *text;
};

/** Print the contents of an array of ints with the given stride.
    Note that size_t is the correct type, as int can overflow. */
void print_some_ints(const int *arr, int length, size_t stride)
{
    int i;
    printf("Address\t\tValue\n");
    for (i=0; i < length; ++i) {
        printf("%p\t%d\n", arr, arr[0]);
        arr = (int *)((unsigned char *)arr + stride);
    }
}

int main(void)
{
    int ints[100] = {0};
    struct MyRecord records[100] = {0};

    print_some_ints(&ints[0], 100, sizeof ints[0]);
    print_some_ints(&records[0].value, 100, sizeof records[0]);
    return 0;
}
</syntaxhighlight>

This idiom is a form of [[type punning]].

===Array cross-section ===
Some languages like [[PL/I]] or [[Fortran]] allow what is known as an ''array cross-section'', which selects certain columns  or rows from a larger array.<ref>{{cite book|last=Hughes|first=Joan K|title=PL/I Structured Programming (second ed.)|year=1979|publisher=John Wiley and Sons|location=New York|isbn=0-471-01908-9|url-access=registration|url=https://archive.org/details/plistructuredpr00hugh}}</ref>{{rp|p.262}}  For example, if a two-dimensional array is declared as
<syntaxhighlight lang="m2">
declare some_array (12,2)fixed;
</syntaxhighlight>
an array of one dimension consisting only of the second column may be referenced as
<syntaxhighlight lang="m2">
some_array(*,2)
</syntaxhighlight>

===Example of multidimensional array with non-unit stride===
Non-unit stride is particularly useful for images. It allows for creating subimages without copying the pixel data. Java example:

<syntaxhighlight lang="java">
public class GrayscaleImage {
    private final int width, height, widthStride;
    /** Pixel data. Pixel in single row are always considered contiguous in this example. */
    private final byte[] pixels;
    /** Offset of the first pixel within pixels */
    private final int offset;

    /** Constructor for contiguous data */
    public Image(int width, int height, byte[] pixels) {
        this.width = width;
        this.height = height;
        this.pixels = pixels;
        this.offset = 0;
        this.widthStride = width;
    }

    /** Subsection constructor */
    public Image(int width, int height, byte[] pixels, int offset, int widthStride) {
        this.width = width;
        this.height = height;
        this.pixels = pixels;
        this.offset = offset;
        this.widthStride = widthStride;
    }

    /** Returns a subregion of this Image as a new Image. This and the new image share
        the pixels, so changes to the returned image will be reflected in this image. */
    public Image crop(int x1, int y1, int x2, int y2) {
        return new Image(x2 - x1, y2 - y1, pixels, offset + y1 * widthStride + x1, widthStride);
    }

    /** Returns pixel value at specified coordinate */
    public byte getPixelAt(int x, int y) {
        return pixels[offset + y * widthStride + x];
    }
}
</syntaxhighlight>