Pointers and Arrays in C#
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In this ninth part of a ten-part series that covers C# in depth, you will learn about pointers, arrays, and more. This article is excerpted from chapter four of
C# 3.0 in a Nutshell, Third Edition, A Desktop Quick Reference, written by Joseph Albahari and Ben Albahari (O'Reilly; ISBN: 0596527578). Copyright © 2007 O'Reilly Media, Inc. All rights reserved. Used with permission from the publisher. Available from booksellers or direct from O'Reilly Media.
Attribute Targets
Implicitly, the target of an attribute is the code element it immediately precedes, which is typically a type or type member. You can also attach attributes, however, to an assembly. This requires that you explicitly specify the attribute’s target.
Here is an example of using theCLSCompliantattribute to specify CLS compliance for an entire assembly:
[assembly:CLSCompliant(true)]
Specifying Multiple Attributes
Multiple attributes can be specified for a single code element. Each attribute can be listed either within the same pair of square brackets (separated by a comma) or in separate pairs of square brackets (or a combination of the two). The following three examples are semantically identical:
[Serializable, Obsolete, CLSCompliant(false)]
public class Bar {...}
[Serializable] [Obsolete] [CLSCompliant(false)]
public class Bar {...}
[Serializable, Obsolete]
[CLSCompliant(false)]
public class Bar {...}
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 shows the main pointer operators.
Table 4-2. 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 whichx->yis 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 RedFilter(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 is no overhead associated with leaving the managed execution environment.
Next: The fixed Statement >>
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 This article is excerpted from chapter four of C# 3.0 in a Nutshell, Third Edition, A Desktop Quick Reference, written by Joseph Albahari and Ben Albahari (O'Reilly; ISBN: 0596527578). Check it out today at your favorite bookstore. Buy this book now.
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