How to compile unsafe code in C#?

Unsafe code in C# allows direct memory manipulation using pointers, which bypasses the .NET garbage collector's safety mechanisms. To compile unsafe code, you need to enable unsafe context compilation through specific compiler settings.

Command-Line Compilation

For compiling unsafe code using the command-line compiler, you must specify the /unsafe switch −

csc /unsafe filename.cs

For example, to compile a program named one.cs containing unsafe code −

csc /unsafe one.cs

Visual Studio IDE Configuration

In Visual Studio, you need to enable unsafe code compilation in the project properties. Follow these steps −

• Open Project Properties by right-clicking the project in Solution Explorer and selecting "Properties"
• Click on the "Build" tab
• Check the option "Allow unsafe code"
• Save and rebuild your project

Modern .NET Project Files

For modern .NET projects using SDK-style project files, you can enable unsafe code by adding the following property to your .csproj file −

<PropertyGroup>
  <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
</PropertyGroup>

Example of Unsafe Code Compilation

Here's a simple example showing how unsafe code works once compilation is enabled −

using System;

class Program {
    static unsafe void Main() {
        int number = 42;
        int* ptr = &number;
        
        Console.WriteLine("Value: " + number);
        Console.WriteLine("Address: " + (long)ptr);
        Console.WriteLine("Value via pointer: " + *ptr);
        
        *ptr = 100;
        Console.WriteLine("New value: " + number);
    }
}

The output of the above code is −

Value: 42
Address: 140734516744220
Value via pointer: 42
New value: 100

Conclusion

Compiling unsafe code in C# requires enabling unsafe context through the /unsafe compiler switch, Visual Studio project settings, or the AllowUnsafeBlocks property in modern .NET projects. Once enabled, you can use pointers and direct memory manipulation within unsafe blocks or methods.