Example code showing the behavior of `std.Io.File.Reader.atEnd`

reader_atEnd.zig

const std = @import("std");

pub fn main(init: std.process.Init) !void {
    const io = init.io;
    const cwd = std.Io.Dir.cwd();

    // Create a test file
    {
        const f = try cwd.createFile(io, "demo.txt", .{});
        defer f.close(io);
        _ = try f.writePositionalAll(io, "hello", 0);
    }
    defer cwd.deleteFile(io, "demo.txt") catch {};

    var file = try cwd.openFile(io, "demo.txt", .{});
    defer file.close(io);

    var buf: [16]u8 = undefined;
    var file_reader = file.reader(io, &buf);

    // 1. Fresh reader: size is null → atEnd false (unknown case)
    std.debug.print("fresh:         atEnd = {}\n", .{file_reader.atEnd()});

    // 2. Populate size via getSize, pos still 0 → atEnd false (genuinely not at end)
    _ = try file_reader.getSize();
    std.debug.print("after getSize: atEnd = {}\n", .{file_reader.atEnd()});

    // 3. Drain the file → pos == size → atEnd true
    var dump: [16]u8 = undefined;
    const n = try file_reader.interface.readSliceShort(&dump);
    std.debug.print("read {} bytes: atEnd = {}\n", .{ n, file_reader.atEnd() });
}

// ~/.local/share/zig/0.16.0/zig run reader_atEnd.zig
// Output:
// fresh:         atEnd = false
// after getSize: atEnd = false
// read 5 bytes: atEnd = true