.net barcode reader free Part II Designing Types in .net C#

Drawer pdf417 in .net C# Part II Designing Types

The following sections go into a little more detail about each of these items and introduce a few possibilities for the way the Microsoft Office system can help you address them.

10 10 12 13 13

For faster compilation, you can always forward-declare the classes you re going to use in your header files, and include just the definitions you require, although there s no guarantee that under-the-hood QtWebKit headers are doing the same thing.

PPTP encapsulates PPP frames in IP datagrams for transmission over an IP internetwork, such as the Internet. PPTP can be used for remote access and site-to-site VPN connections. PPTP is documented in RFC 2637. PPTP uses a TCP connection for tunnel management and a modified version of Generic Routing Encapsulation (GRE) to encapsulate PPP frames for tunneled data. The payloads of the encapsulated PPP frames can be encrypted, compressed, or both. Figure 2-6 shows the structure of a PPTP packet containing an IP datagram.

Key Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-42

To control which computer games your child is allowed to play, in the User Controls window (shown in Figure 10-21), click Games. From the window shown in Figure 1024, click Set Game Ratings to specify the ratings codes for allowable games. You can also block games that contain specific types of objectionable content, even if the game s rating falls into the acceptable range. (Scroll down on the game ratings page to see these types of content, many of which you probably never imagined could appear in something called a game. ) In addition, you can review a list of installed games and explicitly block or allow certain titles.

In some languages, such as unmanaged C++, it is possible to declare methods or parameters as a constant that forbids the code in an instance method from changing any of the object s fields or prevents the code from modifying any of the objects passed into the method . The CLR does not provide for this, and many programmers have been lamenting this missing feature . Since the CLR doesn t offer this feature, no language (including C#) can offer this feature . First, you should note that in unmanaged C++, marking an instance method or parameter as const ensured only that the programmer could not write normal code that would modify the object or parameter . Inside the method, it was always possible to write code that could mutate the object/parameter by either casting away the const-ness or by getting the address of the object/argument and then writing to the address . In a sense, unmanaged C++ lied to programmers, making them believe that their constant objects/arguments couldn t be written to even though they could . When designing a type s implementation, the developer can just avoid writing code that manipulates the object/arguments . For example, strings are immutable because the String class doesn t offer any methods that can change a string object . Also, it would be very difficult for Microsoft to endow the CLR with the ability to verify that a constant object/argument isn t being mutated . The CLR would have to verify at each write that the write was not occurring to a constant object, and this would hurt performance significantly . Of course, a detected violation would result in the CLR throwing an exception . Furthermore, constant support adds a lot of complexity for developers . For example, if a type is immutable, all derived types would have to respect this . In addition, an immutable type would probably have to consist of fields that are also of immutable types . These are just some of the reasons why the CLR does not support constant objects/arguments .

You can pass an assembly qualified type string, such as System.Int32, mscorlib, Version=1.0.2411.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 , to GetType. In this case, GetType will look for the type in the specified assembly (loading the assembly if necessary). The System.Type type offers the following instance methods: GetNestedType and GetNestedTypes. The System.Reflection.Assembly type offers the following instance methods: GetType, GetTypes, and GetExportedTypes. The System.Reflection.Module type offers the following instance methods: GetType, GetTypes, and FindTypes. Many programming languages also offer an operator that allows you to obtain a Type object from a type name. When possible, you should use this operator to obtain a reference to a Type instead of using any of the methods in the preceding list because the operator generally produces faster code. In C#, the operator is called typeof. The following code demonstrates how to use it:

Listing 4-2: OutputDebugStringEvent from PROCESSDEBUGEVENTS.CPP static DWORD OutputDebugStringEvent pUserClass , , DWORD dwProcessId , DWORD dwThreadId ) { // OutputDebugString can dump huge numbers of characters so I'll 175 , OUTPUT_DEBUG_STRING_INFO & stODSI ( CDebugBaseUser * pData

14

This is a simple example, but you can probably imagine a program in which the information about the phone-number length is needed in many places. At the time you create the program, the employees all live in one country, so you need only seven digits for their phone numbers. As the company expands and branches are established in different countries, you ll need longer phone numbers. If you have parameterized, you can make the change in only one place: in the definition of the named constant LOCAL_NUMBER_LENGTH. As you might expect, the use of named constants has been shown to greatly aid program maintenance. As a general rule, any technique that centralizes control over things that might change is a good technique for reducing maintenance efforts (Glass 1991).