unsafe block
Learn the unsafe block and pointer usage.
What is an unsafe block?
An unsafe block is a special code region in C# that allows pointer usage. Pointers hold raw memory addresses, which steps outside the normal C# rules.
To use unsafe, the project must enable <AllowUnsafeBlocks>true</AllowUnsafeBlocks>. An unsafe block lets you write code where the GC cannot move objects. This is preferred in performance-critical scenarios.
When is unsafe used?
unsafe code is typically used in performance-critical areas such as game engines, image processing and native library wrappers. It is rarely needed in everyday code because pointer errors can cause crashes and security holes.
Modern C# offers Span<T> and ref struct types that safely replace many uses of unsafe. So unsafe is reached for only when truly necessary.
Exercise Print a value with an unsafe method
Define an unsafe static void Touch() method. In its body write int x = 10; and int* p = &x;, then print the value with Console.WriteLine(*p);. Call Touch(); from Main.
Show example solution
unsafe static void Touch() { int x = 10; int* p = &x; Console.WriteLine(*p); }
Example solution:
using System;
class Program
{
unsafe static void Touch()
{
int x = 10;
int* p = &x;
Console.WriteLine(*p);
}
static void Main()
{
Touch();
}
}Test yourself
-
What does an unsafe block enable?
- Pointer usage
- Faster GC
- Shorter code
- Automatic memory management
Show answer
Pointer usage — Correct. Pointers such as int* can be used inside an unsafe block.
-
Complete the unsafe method
public ____ void DoWork() { int x = 5; int* p = &x; }Show answer
public unsafe void DoWork() { int x = 5; int* p = &x; } -
What is required to use unsafe?
- Only async
- Only static
- AllowUnsafeBlocks in the project
- Nothing
Show answer
AllowUnsafeBlocks in the project — Correct. The AllowUnsafeBlocks project setting must be on.