Arrays

Arrays

arrays.zig

const assert = @import("std").debug.assert;
const mem = @import("std").mem;

// array literal
const message = [_]u8{ 'h', 'e', 'l', 'l', 'o' };

// get the size of an array
comptime {
    assert(message.len == 5);
}

// a string literal is an array literal
const same_message = "hello";

comptime {
    assert(mem.eql(u8, message, same_message));
    assert(@typeOf(message) == @typeOf(same_message));
}

test "iterate over an array" {
    var sum: usize = 0;
    for (message) |byte| {
        sum += byte;
    }
    assert(sum == usize('h') + usize('e') + usize('l') * 2 + usize('o'));
}

// modifiable array
var some_integers: [100]i32 = undefined;

test "modify an array" {
    for (some_integers) |*item, i| {
        item.* = @intCast(i32, i);
    }
    assert(some_integers[10] == 10);
    assert(some_integers[99] == 99);
}

// array concatenation works if the values are known
// at compile time
const part_one = [_]i32{ 1, 2, 3, 4 };
const part_two = [_]i32{ 5, 6, 7, 8 };
const all_of_it = part_one ++ part_two;
comptime {
    assert(mem.eql(i32, all_of_it, [_]i32{ 1, 2, 3, 4, 5, 6, 7, 8 }));
}

// remember that string literals are arrays
const hello = "hello";
const world = "world";
const hello_world = hello ++ " " ++ world;
comptime {
    assert(mem.eql(u8, hello_world, "hello world"));
}

// ** does repeating patterns
const pattern = "ab" ** 3;
comptime {
    assert(mem.eql(u8, pattern, "ababab"));
}

// initialize an array to zero
const all_zero = [_]u16{0} ** 10;

comptime {
    assert(all_zero.len == 10);
    assert(all_zero[5] == 0);
}

// use compile-time code to initialize an array
var fancy_array = init: {
    var initial_value: [10]Point = undefined;
    for (initial_value) |*pt, i| {
        pt.* = Point{
            .x = @intCast(i32, i),
            .y = @intCast(i32, i) * 2,
        };
    }
    break :init initial_value;
};
const Point = struct {
    x: i32,
    y: i32,
};

test "compile-time array initalization" {
    assert(fancy_array[4].x == 4);
    assert(fancy_array[4].y == 8);
}

// call a function to initialize an array
var more_points = [_]Point{makePoint(3)} ** 10;
fn makePoint(x: i32) Point {
    return Point{
        .x = x,
        .y = x * 2,
    };
}
test "array initialization with function calls" {
    assert(more_points[4].x == 3);
    assert(more_points[4].y == 6);
    assert(more_points.len == 10);
}
``` ```
$ zig test arrays.zig
1/4 test "iterate over an array"...OK
2/4 test "modify an array"...OK
3/4 test "compile-time array initalization"...OK
4/4 test "array initialization with function calls"...OK
All tests passed.

See also:

• for
• Slices

Multidimensional Arrays

Mutlidimensional arrays can be created by nesting arrays:

multidimensional.zig

const std = @import("std");
const assert = std.debug.assert;

const mat4x4 = [4][4]f32{
    [_]f32{ 1.0, 0.0, 0.0, 0.0 },
    [_]f32{ 0.0, 1.0, 0.0, 1.0 },
    [_]f32{ 0.0, 0.0, 1.0, 0.0 },
    [_]f32{ 0.0, 0.0, 0.0, 1.0 },
};
test "multidimensional arrays" {
    // Access the 2D array by indexing the outer array, and then the inner array.
    assert(mat4x4[1][1] == 1.0);

    // Here we iterate with for loops.
    for (mat4x4) |row, row_index| {
        for (row) |cell, column_index| {
            if (row_index == column_index) {
                assert(cell == 1.0);
            }
        }
    }
}
``` ```
$ zig test multidimensional.zig
1/1 test "multidimensional arrays"...OK
All tests passed.