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Home Forums How do you serialize and save an object to a binary file? – MindStick
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1 Answers

Anubhav Sharma
Anubhav Sharma 23 May 2025
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To serialize and save an object to a binary file in C#, you can use the BinaryFormatter class (for legacy .NET Framework) or System.Text.Json or System.Runtime.Serialization.Formatters.Binary with caution.

Note: BinaryFormatter is obsolete and insecure in .NET Core and .NET 5+. For newer projects, consider alternatives like System.Text.Json, Json.NET, or custom binary formats using System.IO.

1. Binary Serialization (Legacy, .NET Framework)

using System;
using System.IO;
using System.Runtime.Serialization.Formatters.Binary;

[Serializable]
public class Person
{
    public string Name;
    public int Age;
}

var person = new Person { Name = "John", Age = 30 };

using (FileStream fs = new FileStream("person.dat", FileMode.Create))
{
    BinaryFormatter formatter = new BinaryFormatter();
    formatter.Serialize(fs, person);
}

To deserialize:

using (FileStream fs = new FileStream("person.dat", FileMode.Open))
{
    BinaryFormatter formatter = new BinaryFormatter();
    Person deserializedPerson = (Person)formatter.Deserialize(fs);
    Console.WriteLine(deserializedPerson.Name);
}

Warnings:

  • BinaryFormatter is insecure for untrusted data.
  • Use only for internal apps where input is trusted.

2. Use System.Text.Json (Recommended for modern apps, JSON format)

For safety and cross-platform compatibility:

using System.Text.Json;

var person = new Person { Name = "Alice", Age = 25 };
string json = JsonSerializer.Serialize(person);
File.WriteAllText("person.json", json);

To deserialize:

string json = File.ReadAllText("person.json");
Person person = JsonSerializer.Deserialize<Person>(json);

3. Use FileStream and BinaryWriter (Manual Binary Writing)

If you want custom binary serialization:

using (var fs = new FileStream("person.bin", FileMode.Create))
using (var writer = new BinaryWriter(fs))
{
    writer.Write("Alice");
    writer.Write(25);
}

And to read it back:

using (var fs = new FileStream("person.bin", FileMode.Open))
using (var reader = new BinaryReader(fs))
{
    string name = reader.ReadString();
    int age = reader.ReadInt32();
}

Summary

Method Format Safe for modern use .NET Version Notes
BinaryFormatter Binary No .NET Framework Obsolete and insecure
System.Text.Json JSON Yes .NET Core+ Recommended
BinaryWriter/BinaryReader Binary Yes All Manual, needs structure
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