ArrayList

The std.ArrayList is commonly used throughout Zig, and serves as a buffer that can change in size. std.ArrayList(T) is similar to C++'s std::vector<T> and Rust's Vec<T>. The deinit() method frees all of the ArrayList's memory. The memory can be read from and written to via its slice field - .items.

Here we will introduce the usage of the testing allocator. This is a special allocator that only works in tests and can detect memory leaks. In your code, use whatever allocator is appropriate.

const std = @import("std");
const expect = std.testing.expect;

const eql = std.mem.eql;
const ArrayList = std.ArrayList;
const test_allocator = std.testing.allocator;

test "arraylist" {
    var list: ArrayList(u8) = .empty;
    defer list.deinit(test_allocator);
    try list.append(test_allocator, 'H');
    try list.append(test_allocator, 'e');
    try list.append(test_allocator, 'l');
    try list.append(test_allocator, 'l');
    try list.append(test_allocator, 'o');
    try list.appendSlice(test_allocator, " World!");

    try expect(eql(u8, list.items, "Hello World!"));
}

Coming from C++?

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Zig's std.ArrayList is very comparable to C++'s std::vector.