Read and write fixed text

Intermediate · C#. Fixed-capacity text preserves the complete field when read. Writing shorter text fills the remaining space with zeros.

Run this example

Prerequisites: the repository's .NET 10 SDK and a checkout of this source. Run from the repository root:

dotnet run --project docs/examples/CStructSharp.Docs.Examples.csproj -c Release -- fixed-text

The runner checks ABC followed by a zero character; XY writes 58 59 00 00. Success includes PASS fixed-text.

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Complete program

The layout, options, input bytes, helper methods, and required types are all included. To adapt it outside the repository, create a .NET 10 console project, add CStructSharp, and replace Program.cs with this complete file. These examples follow the source version; use a matching package when testing a release.

Download the complete C# source.

// Generated from executable documentation examples. Edit the source region, then regenerate.
using System;
using System.IO;
using System.IO.Pipelines;
using System.Linq;
using System.Buffers;
using System.Collections.Generic;
using System.Dynamic;
using System.Globalization;
using System.Numerics;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Threading.Tasks;
using CStructSharp;
using CStructSharp.Codecs;
using CStructSharp.Diagnostics;
using CStructSharp.Introspection;
using CStructSharp.Values;

internal static partial class Program
{
    public static void Main()
    {
        FixedText();
        Console.WriteLine("PASS fixed-text");
    }

    private static void FixedText()
    {
        var layout = new CStruct("struct label { char text[4]; };");
        StructValue value = layout.Parse(new byte[] { 0x41, 0x42, 0x43, 0x00 }, "label");
        Equal("ABC\0", value.Get<string>("text"));
        SequenceEqual(
            [0x58, 0x59, 0x00, 0x00],
            layout.Serialize("label", new Dictionary<string, object?> { ["text"] = "XY" }));
    }

    private static void Equal<T>(T expected, T actual)
    {
        if (!EqualityComparer<T>.Default.Equals(expected, actual))
        {
            throw new InvalidOperationException($"Expected '{expected}', received '{actual}'.");
        }
    }

    private static void SequenceEqual(byte[] expected, byte[] actual)
    {
        if (!expected.AsSpan().SequenceEqual(actual))
        {
            throw new InvalidOperationException(
                $"Expected {Convert.ToHexString(expected)}, received {Convert.ToHexString(actual)}.");
        }
    }
}

Try it and diagnose mistakes

Try writing ABCDE into four bytes.

Answer: The write fails because the text exceeds the field capacity. The program contains assertions for its original inputs. When changing an input intentionally, update the expected assertion too; an unchanged assertion is not evidence that the new value is wrong.

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