Unsafe code and pointers (C# Programming Guide)
To maintain type safety and security, C# does not support pointer arithmetic, by default. However, by using the unsafe keyword, you can define an unsafe context in which pointers can be used. For more information about pointers, see Pointer types.
In the common language runtime (CLR), unsafe code is referred to as unverifiable code. Unsafe code in C# is not necessarily dangerous; it is just code whose safety cannot be verified by the CLR. The CLR will therefore only execute unsafe code if it is in a fully trusted assembly. If you use unsafe code, it is your responsibility to ensure that your code does not introduce security risks or pointer errors.
Unsafe code overview
Unsafe code has the following properties:
Methods, types, and code blocks can be defined as unsafe.
In some cases, unsafe code may increase an application's performance by removing array bounds checks.
Unsafe code is required when you call native functions that require pointers.
Using unsafe code introduces security and stability risks.
The code that contains unsafe blocks must be compiled with the -unsafe compiler option.
For more information, see:
C# language specification