Arrays
zig
const expect = @import("std").testing.expect;
const assert = @import("std").debug.assert;
const mem = @import("std").mem;
// array literal
const message = [_]u8{ 'h', 'e', 'l', 'l', 'o' };
// alternative initialization using result location
const alt_message: [5]u8 = .{ 'h', 'e', 'l', 'l', 'o' };
comptime {
assert(mem.eql(u8, &message, &alt_message));
}
// get the size of an array
comptime {
assert(message.len == 5);
}
// A string literal is a single-item pointer to an array.
const same_message = "hello";
comptime {
assert(mem.eql(u8, &message, same_message));
}
test "iterate over an array" {
var sum: usize = 0;
for (message) |byte| {
sum += byte;
}
try expect(sum == 'h' + 'e' + 'l' * 2 + 'o');
}
// modifiable array
var some_integers: [100]i32 = undefined;
test "modify an array" {
for (&some_integers, 0..) |*item, i| {
item.* = @intCast(i);
}
try expect(some_integers[10] == 10);
try expect(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, 0..) |*pt, i| {
pt.* = Point{
.x = @intCast(i),
.y = @intCast(i * 2),
};
}
break :init initial_value;
};
const Point = struct {
x: i32,
y: i32,
};
test "compile-time array initialization" {
try expect(fancy_array[4].x == 4);
try expect(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" {
try expect(more_points[4].x == 3);
try expect(more_points[4].y == 6);
try expect(more_points.len == 10);
}shell
$ zig test test_arrays.zig
1/4 test_arrays.test.iterate over an array...OK
2/4 test_arrays.test.modify an array...OK
3/4 test_arrays.test.compile-time array initialization...OK
4/4 test_arrays.test.array initialization with function calls...OK
All 4 tests passed.See also:
Multidimensional Arrays
Multidimensional arrays can be created by nesting arrays:
zig
const std = @import("std");
const expect = std.testing.expect;
const expectEqual = std.testing.expectEqual;
const mat4x5 = [4][5]f32{
[_]f32{ 1.0, 0.0, 0.0, 0.0, 0.0 },
[_]f32{ 0.0, 1.0, 0.0, 1.0, 0.0 },
[_]f32{ 0.0, 0.0, 1.0, 0.0, 0.0 },
[_]f32{ 0.0, 0.0, 0.0, 1.0, 9.9 },
};
test "multidimensional arrays" {
// mat4x5 itself is a one-dimensional array of arrays.
try expectEqual(mat4x5[1], [_]f32{ 0.0, 1.0, 0.0, 1.0, 0.0 });
// Access the 2D array by indexing the outer array, and then the inner array.
try expect(mat4x5[3][4] == 9.9);
// Here we iterate with for loops.
for (mat4x5, 0..) |row, row_index| {
for (row, 0..) |cell, column_index| {
if (row_index == column_index) {
try expect(cell == 1.0);
}
}
}
// Initialize a multidimensional array to zeros.
const all_zero: [4][5]f32 = .{.{0} ** 5} ** 4;
try expect(all_zero[0][0] == 0);
}shell
$ zig test test_multidimensional_arrays.zig
1/1 test_multidimensional_arrays.test.multidimensional arrays...OK
All 1 tests passed.Sentinel-Terminated Arrays
The syntax [N:x]T describes an array which has a sentinel element of value x at the index corresponding to the length N.
zig
const std = @import("std");
const expect = std.testing.expect;
test "0-terminated sentinel array" {
const array = [_:0]u8{ 1, 2, 3, 4 };
try expect(@TypeOf(array) == [4:0]u8);
try expect(array.len == 4);
try expect(array[4] == 0);
}
test "extra 0s in 0-terminated sentinel array" {
// The sentinel value may appear earlier, but does not influence the compile-time 'len'.
const array = [_:0]u8{ 1, 0, 0, 4 };
try expect(@TypeOf(array) == [4:0]u8);
try expect(array.len == 4);
try expect(array[4] == 0);
}shell
$ zig test test_null_terminated_array.zig
1/2 test_null_terminated_array.test.0-terminated sentinel array...OK
2/2 test_null_terminated_array.test.extra 0s in 0-terminated sentinel array...OK
All 2 tests passed.See also:
Destructuring Arrays
Arrays can be destructured:
zig
const print = @import("std").debug.print;
fn swizzleRgbaToBgra(rgba: [4]u8) [4]u8 {
// readable swizzling by destructuring
const r, const g, const b, const a = rgba;
return .{ b, g, r, a };
}
pub fn main() void {
const pos = [_]i32{ 1, 2 };
const x, const y = pos;
print("x = {}, y = {}\n", .{x, y});
const orange: [4]u8 = .{ 255, 165, 0, 255 };
print("{any}\n", .{swizzleRgbaToBgra(orange)});
}shell
$ zig build-exe destructuring_arrays.zig
$ ./destructuring_arrays
x = 1, y = 2
{ 0, 165, 255, 255 }See also: