How do you serialize and save an object to a binary file?

Question

Anubhav Kumar · Answer

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Note: BinaryFormatter is obsolete and insecure in .NET Core and .NET 5+.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.Deserializeandlt;Personandgt;(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
and

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How do you serialize and save an object to a binary file?

Ravi Vishwakarma

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1 Answers

1. Binary Serialization (Legacy, .NET Framework)

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

3. Use `FileStream` and `BinaryWriter` (Manual Binary Writing)

Summary

Liked By

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