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unsafe (C# Reference)

The unsafe keyword denotes an unsafe context, which is required for any operation involving pointers. For more information, see Unsafe Code and Pointers (C# Programming Guide).

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.

// compile with: /unsafe 

class UnsafeTest
{
   // Unsafe method: takes pointer to int: 
   unsafe static void SquarePtrParam(int* p)
   {
      *p *= *p;
   }

   unsafe static void Main()
   {
      int i = 5;
      // Unsafe method: uses address-of operator (&):
      SquarePtrParam(&i);
      Console.WriteLine(i);
   }
}
// Output: 25

For more information, see the following sections in the C# Language Specification:

  • 18 Unsafe code

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