🚀 C# Unsafe Code – Use Pointers and Direct Memory Access

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🧲 Introduction – Why Use Unsafe Code in C#

C# is designed to be a safe, managed language, meaning it automatically handles memory allocation and prevents memory corruption. However, in some cases—such as interfacing with unmanaged APIs, high-performance computing, or system-level programming—you may need direct memory access. C# supports this through unsafe code blocks.

🎯 In this guide, you’ll learn:

• What unsafe code is and how to enable it
• How to use pointers and fixed buffers
• The unsafe, fixed, and stackalloc keywords
• When and why to use unsafe code responsibly

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🔍 Core Concept – What Is Unsafe Code?

Unsafe code refers to C# code blocks that allow direct memory access using pointers, similar to C and C++. You can:

• Declare and use pointers
• Perform pointer arithmetic
• Fix variables in memory to prevent garbage collection from relocating them

⚠️ Unsafe code must be explicitly enabled, and it bypasses .NET’s safety checks.

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🔒 Enabling Unsafe Code in Your Project

🔹 In Visual Studio:

• Right-click the project > Properties > Build
• Check “Allow unsafe code”

🔹 In .NET CLI:

dotnet build -p:AllowUnsafeBlocks=true

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🧪 Basic Syntax – unsafe Keyword

unsafe
{
    int x = 10;
    int* ptr = &x;
    Console.WriteLine((int)ptr);     // Memory address
    Console.WriteLine(*ptr);         // Value at address
}

✅ unsafe allows pointer operations
✅ * dereferences the pointer
✅ & gets the memory address of a variable

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🔧 Using fixed to Pin Variables

Since the garbage collector may move objects around in memory, the fixed keyword pins a variable so its address doesn’t change.

unsafe
{
    int[] numbers = { 1, 2, 3 };
    fixed (int* p = numbers)
    {
        Console.WriteLine(p[0]); // Access array via pointer
    }
}

✅ Use fixed for arrays or fields when you need a stable pointer reference.

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⚙️ stackalloc for Stack Allocation

The stackalloc keyword allocates memory on the stack instead of the heap—ideal for short-lived buffers.

unsafe
{
    int* buffer = stackalloc int[3];
    buffer[0] = 100;
    Console.WriteLine(buffer[0]); // Output: 100
}

✅ Faster than heap allocation
✅ Automatically deallocated when the method exits

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📘 Use Cases for Unsafe Code

• High-performance algorithms (e.g., image processing)
• Interop with native libraries (C/C++)
• Operating system or embedded-level programming
• Writing custom memory buffers or unmanaged data structures

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💡 Tips, Pitfalls & Best Practices

💡 Tip: Wrap unsafe code in small, well-isolated methods.

⚠️ Pitfall: Unsafe code can lead to buffer overflows, memory leaks, and undefined behavior.

📘 Best Practice: Avoid unsafe code unless necessary. Always validate pointer access and bounds.

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📌 Summary – Recap & Next Steps

Unsafe code in C# provides low-level control when you need it, but it comes with risks and responsibility. Use it only when managed alternatives are insufficient.

🔍 Key Takeaways:

• Use unsafe to enable pointer operations
• Use fixed to prevent variables from moving in memory
• Use stackalloc for fast, temporary memory buffers
• Enable unsafe code explicitly in your project

⚙️ Next up: Explore 🚀 C# Multithreading to learn how to run code concurrently for better performance.

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❓ FAQ – C# Unsafe Code

❓ What is unsafe code in C#?
✅ Code that uses pointers and bypasses type/memory safety features.

❓ Is unsafe code allowed by default?
❌ No. You must enable it in project settings or use -p:AllowUnsafeBlocks=true.

❓ Is unsafe code faster?
✅ It can be in performance-critical scenarios, but it requires careful memory management.

❓ Can I use unsafe code in .NET Core or .NET 5/6+?
✅ Yes. All modern .NET versions support unsafe code if enabled.

❓ Should I avoid unsafe code?
✅ Yes, unless you have a strong reason (e.g., interop, performance-critical sections).

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