The unsafe keyword denotes an unsafe context, which is required for any operation involving pointers.

You can use the unsafe modifier in the declaration of a type or a member. The entire textual extent of the type or member is therefore considered an unsafe context. For example, the following is a method declared with the unsafe modifier:

unsafe static void FastCopy ( byte[] src, byte[] dst, int count )
{
   // unsafe context: can use pointers here
}

The scope of the unsafe context extends from the parameter list to the end of the method, so pointers can also be used in the parameter list:

unsafe static void FastCopy ( byte* ps, byte* pd, int count ) {...}

You can also use an unsafe block to enable the use of an unsafe code inside this block. For example:

unsafe 
{
   // unsafe context: can use pointers here
}

To compile unsafe code, you must specify the /unsafe compiler option. Unsafe code is not verifiable by the common language runtime.

Example

// cs_unsafe_keyword.cs
// compile with: /unsafe
using System;
class UnsafeTest 
{
   // unsafe method: takes pointer to int:
   unsafe static void SquarePtrParam (int* p) 
   {
      *p *= *p;
   }
   unsafe public static void Main() 
   {
      int i = 5;
      // unsafe method: uses address-of operator (&)
      SquarePtrParam (&i);
      Console.WriteLine (i);
   }
}

Output

25

See Also

C# Keywords | fixed Statement | Unsafe Code Tutorial | A. Unsafe code