BCL

A rich set of base classes reside directly above the common language runtime in the .NET hierarchy. They are known as the Base Class Libraries (BCL), or sometimes the Framework class libraries (FCL). The BCL include classes, interfaces, and value types that expedite and optimize the development process and provide access to system functionality. To facilitate interoperability among languages, the .NET Base types are Common Language Specification (CLS) compliant, and can therefore be used from any programming language whose compiler conforms to the CLS.

The .NET Framework types are the foundation upon which .NET applications, components, and controls are built. The .NET Framework includes types that perform the following functions:

• Build on the base data types and exceptions

• Perform I/O

• Access information about loaded types

• Invoke .NET Framework security checks

• Provide data access; rich, client-side GUI; and server-controlled, client-side GUI

The BCL provide a rich set of interfaces, as well as abstract and concrete (non-abstract) classes. You can use the concrete classes as is, or, in many cases, derive your own classes from them. To use the functionality of an interface, you can either create a class that implements the interface or derive from one of the .NET Framework classes a class that implements the interface.

The System namespace is the root namespace for fundamental types in the .NET Framework. This namespace includes classes that represent the base data types used by all applications: Object (the root of the inheritance hierarchy), Byte, Char, Array, Int32, String, and so on. Many of these types correspond to the primitive data types that your programming language uses. When you write code using .NET Framework types, you can use your language's corresponding keyword when a .NET Framework base data type is expected.

Table 1.1 lists some of the value types the .NET Framework supplies, briefly describes each type, and indicates the corresponding type in Visual Basic, C#, and the Managed Extensions for C++. The table also includes entries for the Object and String classes, for which many languages have corresponding keywords.

In addition to the base data types, the System namespace contains almost 100 classes, ranging from classes that handle exceptions to classes that deal with core runtime concepts, such as application domains and the garbage collector.

The System namespace also contains many second-level namespaces. Table 1.2 shows the categories of functionality the System namespace covers, the second-level namespaces in each category, and a brief description of each namespace. Although many of the second-level namespaces contain other namespaces, only a few of the third-level namespaces are included in this table.

Table 1.1. The .NET Framework Types

Category	Class Name	Description	Visual Basic Data Type	C# Data Type	Managed Extensions for C++ Data Type	JScript Data Type
Integer	Byte	An 8-bit unsigned integer	Byte	byte	char	byte
	SByte	An 8-bit signed integer; not CLS compliant	Sbyte - No built-in type.	sbyte	signed char	SByte
	Int16	A 16-bit signed integer	Short	short	short	short
	Int32	A 32-bit signed integer	Integer	int -or- long	int	int
	Int64	A 64-bit signed integer	Long	long __int64	long
	UInt16	A 16-bit unsigned integer; not CLS compliant	UInt16 - No built-in type.	ushort	unsigned short	UInt16
	UInt32	A 32-bit unsigned integer; not CLS compliant	UInt32 - No built-in type.	uint	unsigned int -or- unsigned long	UInt32
	UInt64	A 64-bit unsigned integer; not CLS compliant	UInt64 - No built-in type.	ulong	unsigned __int64	UInt64
Floating point	Single	A single-precision (32-bit) floating-point number	Single	float	float	float
	Double	A double-precision (64-bit) floating-point number	Double	double	double	double
Logical	Boolean	A Boolean value (true or false)	Boolean	bool	bool	bool
Other	Char	A Unicode (16-bit) character	Char	char	wchar_t	char
	Decimal	A 96-bit decimal value	Decimal	decimal	Decimal	Decimal
	IntPtr	A signed integer whose size depends on the underlying platform (a 32-bit value on a 32-bit and platform a 64-bit value on a 64-bit platform)	IntPtr - No built-in type.	IntPtr - No built-in type.	IntPtr - No built-in type.	IntPtr
	UintPtr	An unsigned integer whose size depends on the underlying platform (a 32- bit value on a 32-bit platform and a 64-bit value on a 64-bit platform); not CLS compliant	UintPtr - No built-in type.	UintPtr - No built-in type.	UintPtr - No built-in type.	UintPtr
Class objects	Object	The root of the object hierarchy	Object	Object	Object*	Object
	String	An immutable, fixed-length string of Unicode characters	String	String	String*	String

Table 1.2. Functionality Provided by the System Namespace

Category	Namespace	Functionality
Component model	System.CodeDom	Representation of the elements and structure of a source code document, and compilation and handling of such code
	System.ComponentModel	Implementation of components, including licensing and design-time adaptation
	Configuration System.Configuration Data System.Data	Retrieval of application configuration data Access and management of data and data sources
	System.Xml	Standards-based support for processing XML
	System.Xml.Serialization	Bidirectional object-to-XML mapping
Framework services	System.Diagnostics	Application instrumentation and diagnostics
	System.DirectoryServices	Access to the Active Directory of an Active Directory service provider, such as a Windows domain
	System.Management	Services and application management tools that work with the Web-Based Enterprise Management (WBEM) standards
	System.Messaging	Microsoft Message Queue (MSMQ) access and management, and the sending and receiving of messages
	System.ServiceProcess	Installation and execution of Windows-based service applications; does not access specific services, such as Active Directory or XML Web Services
	System.Timers	Event raising on an interval or more complex schedule
Globalization and localization	System.Globalization	Support for internationalization and globalization of code and resources
	System.Resources	Resource management and access, including support for localization
Net System.Net	Support for sending and receiving data over a network, including simple programming interfaces for common network protocols such as HTTP and SMTP
Common tasks	System.Collections	Collections of objects, such as lists, queues, arrays, hash tables, and dictionaries
	System.IO	Basic data stream access and management, including file I/O, memory I/O, and isolated storage
	System.Text	Character encoding, character conversion, and string manipulation
	System.Text.RegularExpressions	Full regular expression support
	System.Threading	Multithreaded programming support, including locking and synchronization
Reflection	System.Reflection	Access to type metadata and dynamic creation and invocation of types
Rich, client-side GUI	System.Windows.Forms	Rich user interface features for Windows-based applications
Runtime infrastructure Services	System.Runtime.CompilerServices	Support for compilers that target the runtime
	System.Runtime.InteropServices	Support for interoperability with COM and other unmanaged code
	System.Runtime.Remoting	Support for creating tightly or loosely coupled distributed applications
	System.Runtime.Serialization	Object serialization and deserialization, including binary and SOAP encoding support
.NET Framework security	System.Security	Access to the underlying mechanisms of the .NET Framework security system, including policy resolution, stack walks, and permissions
	System.Security.Cryptography	Cryptographic services, including encoding and decoding of data, hashing, random number generation, message authentication, and formation of digital signatures
Web Services	System.Web	Support for Web server and client management, communication, and design. Provides core infrastructure for ASP.NET, including Web Forms support
	System.Web.Services	Client- and server-side support for SOAP-based Web services