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C# in a Nutshell
book

C# in a Nutshell

by Ben Albahari, Ted Neward, Peter Drayton
March 2002
Intermediate to advanced content levelIntermediate to advanced
864 pages
31h 8m
English
O'Reilly Media, Inc.
Content preview from C# in a Nutshell

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 value. This is considered to be of type V, but pointer types can be (unsafely) cast to any other pointer type. Table 4-2 lists the main pointer operators.

Table 4-2. Principal pointer operators

Operator

Meaning

&

The address-of operator returns a pointer to the address of a value

*

The dereference operator returns the value 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 with a managed object:

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

Unsafe code typically runs faster than a corresponding safe implementation, which in this case would have required a nested loop with array indexing and bounds ...

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Publisher Resources

ISBN: 0596001819Catalog PageErrata