Zig by Example: Pointers

Pointers are objects that store a memory address.

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

Single-item pointers point to exactly one value.

const Single = *bool;

Many-item pointers point to an unknown number of values. Unless you’re interfacing with C code, you probably won’t use these types of pointers, so we’ll skip over them.

const Many = [*]bool;

All pointers in Zig point to a non-null value. To define a null pointer, you must make the pointer type optional.

const Null = ?*bool;
pub fn main() !void {

To create a single-item pointer, use the & operator.

    var v = false;
    var ptr: *bool = &v;
    print("pointer: {}\n", .{ptr});

To access the value located at the memory address stored by a single-item pointer, use the * operator.

    ptr.* = true;
    print("value: {}\n", .{ptr.*});

If a pointer is const, the value of its pointee can be modified, but the pointer itself cannot be re-assigned.

    const const_ptr: *bool = &v;
    const_ptr.* = false;

If a pointee is const, its pointer type will reflect that. The value of const pointees cannot be modified, but the pointer itself can be re-assigned.

    const cf = false;
    const ct = true;
    var ptr_to_const: *const bool = &cf;
    ptr_to_const = &ct;
$ zig run pointers.zig
pointer: bool@7ff7b26e24a7
value: true

Next example: Slices.