Filesystem

Let’s create and open a file in our current working directory, write to it, and then read from it. Here we have to use .seekTo to go back to the start of the file before reading what we have written.

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

test "createFile, write, seekTo, read" {
    const file = try std.fs.cwd().createFile(
        "junk_file.txt",
        .{ .read = true },
    );
    defer file.close();

    const bytes_written = try file.writeAll("Hello File!");
    _ = bytes_written;

    var buffer: [100]u8 = undefined;
    try file.seekTo(0);
    const bytes_read = try file.readAll(&buffer);

    try expect(eql(u8, buffer[0..bytes_read], "Hello File!"));
}

The functions std.fs.openFileAbsolute and similar absolute functions exist, but we will not test them here.

We can get various information about files by using .stat() on them. Stat also contains fields for .inode and .mode, but they are not tested here as they rely on the current OS’ types.

When the Enum type is known from context, it can be omitted, so we can compare stat.kind to .file instead of Kind.file.

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

test "file stat" {
    const file = try std.fs.cwd().createFile(
        "junk_file2.txt",
        .{ .read = true },
    );
    defer file.close();
    const stat = try file.stat();
    try expect(stat.size == 0);
    try expect(stat.kind == .file);
    try expect(stat.ctime <= std.time.nanoTimestamp());
    try expect(stat.mtime <= std.time.nanoTimestamp());
    try expect(stat.atime <= std.time.nanoTimestamp());
}

We can make directories and iterate over their contents. Here we will use an iterator (discussed later). This directory (and its contents) will be deleted after this test finishes.

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

test "make dir" {
    try std.fs.cwd().makeDir("test-tmp");
    var iter_dir = try std.fs.cwd().openDir(
        "test-tmp",
        .{ .iterate = true },
    );
    defer {
        iter_dir.close();
        std.fs.cwd().deleteTree("test-tmp") catch unreachable;
    }

    _ = try iter_dir.createFile("x", .{});
    _ = try iter_dir.createFile("y", .{});
    _ = try iter_dir.createFile("z", .{});

    var file_count: usize = 0;
    var iter = iter_dir.iterate();
    while (try iter.next()) |entry| {
        if (entry.kind == .file) file_count += 1;
    }

    try expect(file_count == 3);
}