Zig by Example: Pointers

A pointer is an object that stores a memory address. There are three types of pointers in Zig: single-item, many-item, and Slices.

 
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;

Note that all pointers in Zig point to a non-null value. To get null pointers, you need to use Optionals.

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

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

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

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

 
    print("before: {}\n", .{ptr.*});
    ptr.* = false;
    print("after: {}\n", .{ptr.*});

Note that if a value is const, its pointer type is also const.

 
    const const_value = true;
    var ptr_to_const: *const bool = &const_value;
    print("pointer: {}\n", .{ptr_to_const});
}
 
$ zig run pointers.zig
pointer: [email protected]
before: true
after: false
pointer: [email protected]

Next example: Slices.

by Jason Phan | source | license