C# 5.0 Pocket Reference

Unsafe Code and Pointers

C# supports direct memory manipulation via pointers within blocks of code marked unsafe and compiled with the /unsafe compiler option. Pointer types are primarily useful for interoperability with C APIs, but may also be used for accessing memory outside the managed heap or for performance-critical hotspots.

Pointer Basics

For every value type or pointer type V, there is a corresponding pointer type V*. A pointer instance holds the address of a variable. Pointer types can be (unsafely) cast to any other pointer type. The main pointer operators are:

Operator	Meaning
&	The address-of operator returns a pointer to the address of a variable.
*	The dereference operator returns the variable at the address of a pointer.
->	The pointer-to-member operator is a syntactic shortcut, in which x->y is equivalent to (*x).y.

Unsafe Code

By marking a type, type member, or statement block with the unsafe keyword, you’re permitted to use pointer types and perform C++-style pointer operations on memory within that scope. Here is an example of using pointers to quickly process a bitmap:

unsafe void BlueFilter (int[,] bitmap)
{
  int length = bitmap.Length;
  fixed (int* b = bitmap)
  {
    int* p = b;
    for (int i = 0; i < length; i++)
      *p++ &= 0xFF;
  }
}

Unsafe code can run faster than a corresponding safe implementation. In this case, the code would have required a nested loop with array indexing and bounds checking. An unsafe C# method may also be faster than calling an external C function, since there ...