System Namespace

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.NET Framework Class Library
System Namespace

The System namespace contains fundamental classes and base classes that define commonly-used value and reference data types, events and event handlers, interfaces, attributes, and processing exceptions.

Other classes provide services supporting data type conversion, method parameter manipulation, mathematics, remote and local program invocation, application environment management, and supervision of managed and unmanaged applications.

Classes
  Class Description
Public class AccessViolationException The exception that is thrown when there is an attempt to read or write protected memory.
Public class ActivationContext Identifies the activation context for the current application. This class cannot be inherited.
Public class Activator Contains methods to create types of objects locally or remotely, or obtain references to existing remote objects. This class cannot be inherited.
Public class AppDomain Represents an application domain, which is an isolated environment where applications execute. This class cannot be inherited.
Public class AppDomainManager Provides a managed equivalent of an unmanaged host.
Public class AppDomainSetup Represents assembly binding information that can be added to an instance of AppDomain.
Public class AppDomainUnloadedException The exception that is thrown when an attempt is made to access an unloaded application domain.
Public class ApplicationException The exception that is thrown when a non-fatal application error occurs.
Public class ApplicationId Contains information used to uniquely identify an application. This class cannot be inherited.
Public class ApplicationIdentity Provides the ability to uniquely identify a manifest-activated application. This class cannot be inherited.
Public class ArgumentException The exception that is thrown when one of the arguments provided to a method is not valid.
Public class ArgumentNullException The exception that is thrown when a null reference (Nothing in Visual Basic) is passed to a method that does not accept it as a valid argument.
Public class ArgumentOutOfRangeException The exception that is thrown when the value of an argument is outside the allowable range of values as defined by the invoked method.
Public class ArithmeticException The exception that is thrown for errors in an arithmetic, casting, or conversion operation.
Public class Array Provides methods for creating, manipulating, searching, and sorting arrays, thereby serving as the base class for all arrays in the common language runtime.
Public class ArrayTypeMismatchException The exception that is thrown when an attempt is made to store an element of the wrong type within an array.
Public class AssemblyLoadEventArgs Provides data for the AssemblyLoad event.
Public class Attribute Represents the base class for custom attributes.
Public class AttributeUsageAttribute Specifies the usage of another attribute class. This class cannot be inherited.
Public class BadImageFormatException The exception that is thrown when the file image of a DLL or an executable program is invalid.
Public class BitConverter Converts base data types to an array of bytes, and an array of bytes to base data types.
Public class Buffer Manipulates arrays of primitive types.
Public class CannotUnloadAppDomainException The exception that is thrown when an attempt to unload an application domain fails.
Public class CharEnumerator Supports iterating over a String object and reading its individual characters. This class cannot be inherited.
Public class CLSCompliantAttribute Indicates whether a program element is compliant with the Common Language Specification (CLS). This class cannot be inherited.
Public class Console Represents the standard input, output, and error streams for console applications. This class cannot be inherited.
Public class ConsoleCancelEventArgs Provides data for the Console.CancelKeyPress event. This class cannot be inherited.
Public class ContextBoundObject Defines the base class for all context-bound classes.
Public class ContextMarshalException The exception that is thrown when an attempt to marshal an object across a context boundary fails.
Public class ContextStaticAttribute Indicates that the value of a static field is unique for a particular context.
Public class Convert Converts a base data type to another base data type.
Public class DataMisalignedException The exception that is thrown when a unit of data is read from or written to an address that is not a multiple of the data size. This class cannot be inherited.
Public class DBNull Represents a null value.
Public class Delegate Represents a delegate, which is a data structure that refers to a static method or to a class instance and an instance method of that class.
Public class DivideByZeroException The exception that is thrown when there is an attempt to divide an integral or decimal value by zero.
Public class DllNotFoundException The exception that is thrown when a DLL specified in a DLL import cannot be found.
Public class DuplicateWaitObjectException The exception that is thrown when an object appears more than once in an array of synchronization objects.
Public class EntryPointNotFoundException The exception that is thrown when an attempt to load a class fails due to the absence of an entry method.
Public class Environment Provides information about, and means to manipulate, the current environment and platform. This class cannot be inherited.
Public class EventArgs EventArgs is the base class for classes containing event data.
Public class Exception Represents errors that occur during application execution.
Public class ExecutionEngineException The exception that is thrown when there is an internal error in the execution engine of the common language runtime. This class cannot be inherited.
Public class FieldAccessException The exception that is thrown when there is an invalid attempt to access a private or protected field inside a class.
Public class FileStyleUriParser A customizable parser based on the File scheme.
Public class FlagsAttribute Indicates that an enumeration can be treated as a bit field; that is, a set of flags.
Public class FormatException The exception that is thrown when the format of an argument does not meet the parameter specifications of the invoked method.
Public class FtpStyleUriParser A customizable parser based on the File Transfer Protocol (FTP) scheme.
Public class GC Controls the system garbage collector, a service that automatically reclaims unused memory.
Public class GenericUriParser A customizable parser for a hierarchical URI.
Public class GopherStyleUriParser A customizable parser based on the Gopher scheme.
Public class HttpStyleUriParser A customizable parser based on the HTTP scheme.
Public class IndexOutOfRangeException The exception that is thrown when an attempt is made to access an element of an array with an index that is outside the bounds of the array. This class cannot be inherited.
Public class InsufficientMemoryException The exception that is thrown when a check for sufficient available memory fails. This class cannot be inherited.
Public class InvalidCastException The exception that is thrown for invalid casting or explicit conversion.
Public class InvalidOperationException The exception that is thrown when a method call is invalid for the object's current state.
Public class InvalidProgramException The exception that is thrown when a program contains invalid Microsoft intermediate language (MSIL) or metadata. Generally this indicates a bug in the compiler that generated the program.
Public class LdapStyleUriParser A customizable parser based on the Lightweight Directory Access Protocol (LDAP) scheme.
Public class LoaderOptimizationAttribute Used to set the default loader optimization policy for the main method of an executable application.
Public class LocalDataStoreSlot Encapsulates a memory slot to store local data. This class cannot be inherited.
Public class MarshalByRefObject Enables access to objects across application domain boundaries in applications that support remoting.
Public class Math Provides constants and static methods for trigonometric, logarithmic, and other common mathematical functions.
Public class MemberAccessException The exception that is thrown when an attempt to access a class member fails.
Public class MethodAccessException The exception that is thrown when there is an invalid attempt to access a private or protected method inside a class.
Public class MissingFieldException The exception that is thrown when there is an attempt to dynamically access a field that does not exist.
Public class MissingMemberException The exception that is thrown when there is an attempt to dynamically access a class member that does not exist.
Public class MissingMethodException The exception that is thrown when there is an attempt to dynamically access a method that does not exist.
Public class MTAThreadAttribute Indicates that the COM threading model for an application is multithreaded apartment (MTA).
Public class MulticastDelegate Represents a multicast delegate; that is, a delegate that can have more than one element in its invocation list.
Public class MulticastNotSupportedException The exception that is thrown when there is an attempt to combine two delegates based on the Delegate type instead of the MulticastDelegate type. This class cannot be inherited.
Public class NetPipeStyleUriParser A parser based on the NetPipe scheme for the "Indigo" system.
Public class NetTcpStyleUriParser A parser based on the NetTcp scheme for the "Indigo" system.
Public class NewsStyleUriParser A customizable parser based on the news scheme using the Network News Transfer Protocol (NNTP).
Public class NonSerializedAttribute Indicates that a field of a serializable class should not be serialized. This class cannot be inherited.
Public class NotFiniteNumberException The exception that is thrown when a floating-point value is positive infinity, negative infinity, or Not-a-Number (NaN).
Public class NotImplementedException The exception that is thrown when a requested method or operation is not implemented.
Public class NotSupportedException The exception that is thrown when an invoked method is not supported, or when there is an attempt to read, seek, or write to a stream that does not support the invoked functionality.
Public class Nullable Supports a value type that can be assigned a null reference (Nothing in Visual Basic) like a reference type. This class cannot be inherited.
Public class NullReferenceException The exception that is thrown when there is an attempt to dereference a null object reference.
Public class Object Supports all classes in the .NET Framework class hierarchy and provides low-level services to derived classes. This is the ultimate base class of all classes in the .NET Framework; it is the root of the type hierarchy.
Public class ObjectDisposedException The exception that is thrown when an operation is performed on a disposed object.
Public class ObsoleteAttribute Marks the program elements that are no longer in use. This class cannot be inherited.
Public class OperatingSystem Represents information about an operating system, such as the version and platform identifier. This class cannot be inherited.
Public class OperationCanceledException The exception that is thrown in a thread upon cancellation of an operation that the thread was executing.
Public class OutOfMemoryException The exception that is thrown when there is not enough memory to continue the execution of a program.
Public class OverflowException The exception that is thrown when an arithmetic, casting, or conversion operation in a checked context results in an overflow.
Public class ParamArrayAttribute Indicates that the method will allow a variable number of arguments in its invocation. This class cannot be inherited.
Public class PlatformNotSupportedException The exception that is thrown when a feature does not run on a particular platform.
Public class Random Represents a pseudo-random number generator, a device that produces a sequence of numbers that meet certain statistical requirements for randomness.
Public class RankException The exception that is thrown when an array with the wrong number of dimensions is passed to a method.
Public class ResolveEventArgs Provides data for the TypeResolve, ResourceResolve, and AssemblyResolve events.
Public class SerializableAttribute Indicates that a class can be serialized. This class cannot be inherited.
Public class StackOverflowException The exception that is thrown when the execution stack overflows because it contains too many nested method calls. This class cannot be inherited.
Public class STAThreadAttribute Indicates that the COM threading model for an application is single-threaded apartment (STA).
Public class String Represents text as a series of Unicode characters.
Public class StringComparer Represents a string comparison operation that uses specific case and culture-based or ordinal comparison rules.
Public class SystemException Defines the base class for predefined exceptions in the System namespace.
Public class ThreadStaticAttribute Indicates that the value of a static field is unique for each thread.
Public class TimeoutException The exception that is thrown when the time allotted for a process or operation has expired.
Public class TimeZone Represents a time zone.
Public class Type Represents type declarations: class types, interface types, array types, value types, enumeration types, type parameters, generic type definitions, and open or closed constructed generic types.
Public class TypeInitializationException The exception that is thrown as a wrapper around the exception thrown by the class initializer. This class cannot be inherited.
Public class TypeLoadException The exception that is thrown when type-loading failures occur.
Public class TypeUnloadedException The exception that is thrown when there is an attempt to access an unloaded class.
Public class UnauthorizedAccessException The exception that is thrown when the operating system denies access because of an I/O error or a specific type of security error.
Public class UnhandledExceptionEventArgs Provides data for the event that is raised when there is an exception that is not handled by the application domain.
Public class Uri Provides an object representation of a uniform resource identifier (URI) and easy access to the parts of the URI.
Public class UriBuilder Provides a custom constructor for uniform resource identifiers (URIs) and modifies URIs for the Uri class.
Public class UriFormatException The exception that is thrown when an invalid Uniform Resource Identifier (URI) is detected.
Public class UriParser Parses a new URI scheme. This is an abstract class.
Public class UriTypeConverter Converts a String type to a Uri type, and vice versa.
Public class ValueType Provides the base class for value types.
Public class Version Represents the version number for a common language runtime assembly. This class cannot be inherited.
Public class WeakReference Represents a weak reference, which references an object while still allowing that object to be garbage collected.
Interfaces
  Interface Description
Public interface _AppDomain Exposes the public members of the System.AppDomain class to unmanaged code.
Public interface IAppDomainSetup Represents assembly binding information that can be added to an instance of AppDomain.
Public interface IAsyncResult Represents the status of an asynchronous operation.
Public interface ICloneable Supports cloning, which creates a new instance of a class with the same value as an existing instance.
Public interface IComparable Defines a generalized comparison method that a value type or class implements to create a type-specific comparison method.
Public interface IComparable Defines a generalized comparison method that a value type or class implements to create a type-specific comparison method for ordering instances.
Public interface IConvertible Defines methods that convert the value of the implementing reference or value type to a common language runtime type that has an equivalent value.
Public interface ICustomFormatter Defines a method that supports custom, user-defined formatting of the value of an object.
Public interface IDisposable Defines a method to release allocated unmanaged resources.
Public interface IEquatable Defines a generalized method that a value type or class implements to create a type-specific method for determining equality of instances.
Public interface IFormatProvider Provides a mechanism for retrieving an object to control formatting.
Public interface IFormattable Provides functionality to format the value of an object into a string representation.
Public interface IServiceProvider Defines a mechanism for retrieving a service object; that is, an object that provides custom support to other objects.
Structures
  Structure Description
Public structure ArgIterator Represents a variable-length argument list; that is, the parameters of a function that takes a variable number of arguments.
Public structure ArraySegment Delimits a section of a one-dimensional array.
Public structure Boolean Represents a Boolean value.
Public structure Byte Represents an 8-bit unsigned integer.
Public structure Char Represents a Unicode character.
Public structure ConsoleKeyInfo Describes the console key that was pressed, including the character represented by the console key and the state of the SHIFT, ALT, and CTRL modifier keys.
Public structure DateTime Represents an instant in time, typically expressed as a date and time of day.
Public structure Decimal Represents a decimal number.
Public structure Double Represents a double-precision floating-point number.
Public structure Enum Provides the base class for enumerations.
Public structure Guid Represents a globally unique identifier (GUID).
Public structure Int16 Represents a 16-bit signed integer.
Public structure Int32 Represents a 32-bit signed integer.
Public structure Int64 Represents a 64-bit signed integer.
Public structure IntPtr A platform-specific type that is used to represent a pointer or a handle.
Public structure ModuleHandle Represents a runtime handle for a module.
Public structure Nullable Represents an object whose underlying type is a value type that can also be assigned a null reference (Nothing in Visual Basic) like a reference type.
Public structure RuntimeArgumentHandle References a variable-length argument list.
Public structure RuntimeFieldHandle Represents a field using an internal metadata token.
Public structure RuntimeMethodHandle RuntimeMethodHandle is a handle to the internal metadata representation of a method.
Public structure RuntimeTypeHandle Represents a type using an internal metadata token.
Public structure SByte Represents an 8-bit signed integer.
Public structure Single Represents a single-precision floating-point number.
Public structure TimeSpan Represents a time interval.
Public structure TypedReference Describes objects that contain both a managed pointer to a location and a runtime representation of the type that may be stored at that location.
Public structure UInt16 Represents a 16-bit unsigned integer.
Public structure UInt32 Represents a 32-bit unsigned integer.
Public structure UInt64 Represents a 64-bit unsigned integer.
Public structure UIntPtr A platform-specific type that is used to represent a pointer or a handle.
Public structure Void Specifies a return value type for a method that does not return a value.
Delegates
  Delegate Description
Public delegate Action Represents the method that performs an action on the specified object.
Public delegate AppDomainInitializer Represents the callback method to invoke when the application domain is initialized.
Public delegate AssemblyLoadEventHandler Represents the method that handles the AssemblyLoad event of an AppDomain.
Public delegate AsyncCallback References the callback method to be called when the asynchronous operation is completed.
Public delegate Comparison Represents the method that compares two objects of the same type.
Public delegate ConsoleCancelEventHandler Represents the method that will handle the CancelKeyPress event of a System.Console.
Public delegate Converter Represents a method that converts an object from one type to another type.
Public delegate CrossAppDomainDelegate Used by DoCallBack for cross-application domain calls.
Public delegate EventHandler Represents the method that will handle an event that has no event data.
Public delegate EventHandler Represents the method that will handle an event. The generic type argument specifies the type of the event data generated by the event.
Public delegate Predicate Represents the method that defines a set of criteria and determines whether the specified object meets those criteria.
Public delegate ResolveEventHandler Represents the method that handles the TypeResolve, ResourceResolve, and AssemblyResolve events of an AppDomain.
Public delegate UnhandledExceptionEventHandler Represents the method that will handle the event raised by an exception that is not handled by the application domain.
Enumerations
  Enumeration Description
Public enumeration ActivationContext.ContextForm Indicates the context for a manifest-activated application.
Public enumeration AppDomainManagerInitializationOptions Specifies the action that a custom application domain manager takes when initializing a new domain.
Public enumeration AttributeTargets Specifies the application elements on which it is valid to apply an attribute.
Public enumeration Base64FormattingOptions Specifies whether relevant System.Convert.ToBase64CharArray and System.Convert.ToBase64String methods insert line breaks in their output.
Public enumeration ConsoleColor Specifies constants that define foreground and background colors for the console.
Public enumeration ConsoleKey Specifies the standard keys on a console.
Public enumeration ConsoleModifiers Represents the SHIFT, ALT, and CTRL modifier keys on a keyboard.
Public enumeration ConsoleSpecialKey Specifies combinations of modifier and console keys that can interrupt the current process.
Public enumeration DateTimeKind Specifies whether a DateTime object represents a local time, a Coordinated Universal Time (UTC), or is not specified as either local time or UTC.
Public enumeration DayOfWeek Specifies the day of the week.
Public enumeration Environment.SpecialFolder Specifies enumerated constants used to retrieve directory paths to system special folders.
Public enumeration EnvironmentVariableTarget Specifies the location where an environment variable is stored or retrieved in a set or get operation.
Public enumeration GenericUriParserOptions Specifies options for a UriParser.
Public enumeration LoaderOptimization An enumeration used with the LoaderOptimizationAttribute class to specify loader optimizations for an executable.
Public enumeration MidpointRounding Specifies how mathematical rounding methods should process a number that is midway between two numbers.
Public enumeration PlatformID Identifies the operating system, or platform, supported by an assembly.
Public enumeration StringComparison Specifies the culture, case, and sort rules to be used by certain overloads of the String.Compare and String.Equals methods.
Public enumeration StringSplitOptions Specifies whether applicable System.String.Split method overloads include or omit empty substrings from the return value.
Public enumeration TypeCode Specifies the type of an object.
Public enumeration UriComponents Specifies the parts of a Uri.
Public enumeration UriFormat Controls how URI information is escaped.
Public enumeration UriHostNameType Defines host name types for the Uri.CheckHostName method.
Public enumeration UriKind Defines the kinds of Uris for the Uri.IsWellFormedUriString and several System.Uri methods.
Public enumeration UriPartial Defines the parts of a URI for the Uri.GetLeftPart method.