Namespace: System

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.

Members of System Namespace

Class	Description
class Activator	Contains methods to create types of objects locally or remotely, or obtain references to existing remote objects.
class AppDomain	Represents an application domain, which is an isolated environment where applications execute. This class cannot be inherited.
class AppDomainSetup
class AppDomainUnloadedException	The exception that is thrown when an attempt is made to access an unloaded application domain.
class ApplicationException	The exception that is thrown when a non-fatal application error occurs.
class ArgumentException	The exception that is thrown when one of the arguments provided to a method is not valid.
class ArgumentNullException	The exception that is thrown when a null reference () is passed to a method that does not accept it as a valid argument.
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.
class ArithmeticException	The exception that is thrown for errors in an arithmetic, casting, or conversion operation.
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.
class ArrayTypeMismatchException	The exception that is thrown when an attempt is made to store an element of the wrong type within an array.
class AssemblyLoadEventArgs	Provides data for the AppDomain.AssemblyLoad event.
class Attribute	Base class for custom attributes.
class AttributeUsageAttribute	Specifies the usage of another attribute class. This class cannot be inherited.
class BadImageFormatException	The exception that is thrown when the file image of a DLL or an executable program is invalid.
class BitConverter	Converts base data types to an array of bytes, and an array of bytes to base data types.
class Buffer	Manipulates unmanaged memory represented as arrays of bytes.
class CannotUnloadAppDomainException	The exception that is thrown when an attempt to unload an application domain fails.
class CharEnumerator	Supports iterating over a String and reading its individual characters.
class CLSCompliantAttribute	Indicates whether a program element is compliant with the Common Language Specification (CLS). This class cannot be inherited.
class Console	Represents the standard input, output, and error streams for console applications. This class cannot be inherited.
class ContextBoundObject	Defines the base class for all context-bound classes.
class ContextMarshalException	The exception that is thrown when an attempt to marshal an object across a context boundary fails.
class ContextStaticAttribute	Indicates that the value of a static field is unique for a particular context.
class Convert	Converts a base data type to another base data type.
class DBNull	Represents a null value.
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.
class DivideByZeroException	The exception that is thrown when there is an attempt to divide an integral or decimal value by zero.
class DllNotFoundException	The exception that is thrown when a DLL specified in a DLL import cannot be found.
class DuplicateWaitObjectException	The exception that is thrown when an object appears more than once in an array of synchronization objects.
class EntryPointNotFoundException	The exception that is thrown when an attempt to load a class fails due to the absence of an entry method.
class Enum	Provides the base class for enumerations.
class Environment	Provides information about, and means to manipulate, the current environment and platform. This class cannot be inherited.
class EventArgs	EventArgs is the base class for classes containing event data.
class Exception	Represents errors that occur during application execution.
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.
class FieldAccessException	The exception that is thrown when there is an illegal attempt to access a private or protected field inside a class.
class FlagsAttribute	Indicates that an enumeration can be treated as a bit field; that is, a set of flags.
class FormatException	The exception that is thrown when the format of an argument does not meet the parameter specifications of the invoked method.
class GC	Controls the system garbage collector, a service that automatically reclaims unused memory.
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.
class InvalidCastException	The exception that is thrown for invalid casting or explicit conversion.
class InvalidOperationException	The exception that is thrown when a method call is invalid for the object's current state.
class InvalidProgramException	The exception that is thrown when a program contains invalid Microsoft intermediate language (MSIL) or metadata. Generally this indicates a bug in a compiler.
class LoaderOptimizationAttribute	Used to set the default loader optimization policy for the main method of an executable application.
class LocalDataStoreSlot	Encapsulates a memory slot to store local data. This class cannot be inherited.
class MarshalByRefObject	Enables access to objects across application domain boundaries in applications that support remoting.
class Math	Provides constants and static methods for trigonometric, logarithmic, and other common mathematical functions.
class MemberAccessException	The exception that is thrown when an attempt to access a class member fails.
class MethodAccessException	The exception that is thrown when there is an illegal attempt to access a private or protected method inside a class.
class MissingFieldException	The exception that is thrown when there is an attempt to dynamically access a field that does not exist.
class MissingMemberException	The exception that is thrown when there is an attempt to dynamically access a class member that does not exist.
class MissingMethodException	The exception that is thrown when there is an attempt to dynamically access a method that does not exist.
class MulticastDelegate	Represents a multicast delegate; that is, a delegate that can have more than one element in its invocation list.
class MulticastNotSupportedException	The exception that is thrown when there is an attempt to combine two instances of a non-combinable delegate type unless one of the operands is a null reference (). This class cannot be inherited.
class NonSerializedAttribute	Indicates that a field of a serializable class should not be serialized. This class cannot be inherited.
class NotFiniteNumberException	The exception that is thrown when a floating-point value is positive infinity, negative infinity, or Not-a-Number (NaN).
class NotImplementedException	The exception that is thrown when a requested method or operation is not implemented.
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.
class NullReferenceException	The exception that is thrown when there is an attempt to dereference a null object reference.
class Object	Supports all classes in the .NET Framework class hierarchy and provides low-level services to derived classes. This is the ultimate superclass of all classes in the .NET Framework; it is the root of the type hierarchy.
class ObjectDisposedException	The exception that is thrown when an operation is performed on a disposed object.
class ObsoleteAttribute	Marks the program elements that are no longer in use. This class cannot be inherited.
class OutOfMemoryException	The exception that is thrown when there is not enough memory to continue the execution of a program.
class OverflowException	The exception that is thrown when an arithmetic, casting, or conversion operation in a checked context results in an overflow.
class ParamArrayAttribute	Indicates that the method will allow a variable number of arguments in its invocation. This class cannot be inherited.
class PlatformNotSupportedException	The exception that is thrown when a feature does not run on a particular platform.
class Random	Represents a pseudo-random number generator, a device that produces a sequence of numbers that meet certain statistical requirements for randomness.
class RankException	The exception that is thrown when an array with the wrong number of dimensions is passed to a method.
class ResolveEventArgs	Provides data for the AppDomain.TypeResolve, AppDomain.ResourceResolve, and AppDomain.AssemblyResolve events.
class SerializableAttribute	Indicates that a class can be serialized. This class cannot be inherited.
class StackOverflowException	The exception that is thrown when the execution stack overflows by having too many pending method calls. This class cannot be inherited.
class String	Represents an immutable series of characters.
class SystemException	Defines the base class for predefined exceptions in the System namespace.
class ThreadStaticAttribute	Indicates that the value of a static field is unique for each thread.
class TimeZone	Represents a time zone.
class Type	Represents type declarations: class types, interface types, array types, value types, and enumeration types.
class TypeInitializationException	The exception that is thrown as a wrapper around the exception thrown by the class initializer. This class cannot be inherited.
class TypeLoadException	The exception that is thrown when type-loading failures occur.
class TypeUnloadedException	The exception that is thrown when there is an attempt to access an unloaded class.
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.
class UnhandledExceptionEventArgs	Provides data for the event that is raised when there is an exception that is not handled by the application domain.
class Uri	Provides an object representation of a uniform resource identifier (URI) and easy access to the parts of the URI.
class UriBuilder	Provides a custom constructor for uniform resource indentifiers (URIs) and modifies URIs for the Uri class.
class UriFormatException	The exception that is thrown when an invalid Uniform Resource Identifier (URI) is detected.
class ValueType	Provides the base class for value types.
class Version	Represents the version number for a common language runtime assembly. This class cannot be inherited.
class WeakReference	Represents a weak reference, which references an object while still allowing it to be garbage collected.

Interface	Description
interface _AppDomain	Represents an application domain, which is an isolated environment where applications execute.
interface IAppDomainSetup	Represents assembly binding information that can be added to an instance of AppDomain.
interface IAsyncResult	Represents the status of an asynchronous operation.
interface ICloneable	Supports cloning, which creates a new instance of a class with the same value as an existing instance.
interface IComparable	Defines a generalized comparison method that a value type or class implements to create a type-specific comparison method.
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.
interface ICustomFormatter	Defines a method that supports custom, user-defined formatting of the value of an object.
interface IDisposable	Defines a method to release allocated unmanaged resources.
interface IFormatProvider	Provides a mechanism for retrieving an object to control formatting.
interface IFormattable	Provides functionality to format the value of an object into a string representation.
interface IServiceProvider	Defines a mechanism for retrieving a service object; that is, an object that provides custom support to other objects.

Structure	Description
structure ArgIterator	Represents a variable-length argument list; that is, the parameters of a function that takes a variable number of arguments.
structure Boolean	Represents a Boolean value.
structure Byte	Represents an 8-bit unsigned integer.
structure Char	Represents a Unicode character.
structure DateTime	Represents an instant in time, typically expressed as a date and time of day.
structure Decimal	Represents a decimal number.
structure Double	Represents a double-precision floating point number.
structure Guid	Represents a globally unique identifier (GUID).
structure Int16	Represents a 16-bit signed integer.
structure Int32	Represents a 32-bit signed integer.
structure Int64	Represents a 64-bit signed integer.
structure IntPtr	A platform-specific type that is used to represent a pointer or a handle.
structure RuntimeArgumentHandle	References a variable-length argument list.
structure RuntimeFieldHandle	Represents a field using an internal metadata token.
structure RuntimeMethodHandle	The RuntimeMethodHandle is a handle to the internal metadata representation of a method.
structure RuntimeTypeHandle	Represents a type using an internal metadata token.
structure SByte	Represents an 8-bit signed integer.
structure Single	Represents a single-precision floating point number.
structure TimeSpan	Represents a time interval.
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.
structure UInt16	Represents a 16-bit unsigned integer.
structure UInt32	Represents a 32-bit unsigned integer.
structure UInt64	Represents a 64-bit unsigned integer.
structure UIntPtr	A platform-specific type that is used to represent a pointer or a handle.
structure Void	Indicates a method that does not return a value; that is, the method has the void return type.

Delegate	Description
delegate AssemblyLoadEventHandler	Represents the method that handles the AppDomain.AssemblyLoad event of an AppDomain.
delegate AsyncCallback	References the callback method to be called when the asynchronous operation is completed.
delegate CrossAppDomainDelegate	Used by AppDomain.DoCallBack for cross-application domain calls.
delegate EventHandler	Represents the method that will handle the event that has no event data.
delegate ResolveEventHandler	Represents the method that handles the AppDomain.TypeResolve, AppDomain.ResourceResolve, and AppDomain.AssemblyResolve events of an AppDomain.
delegate UnhandledExceptionEventHandler	Represents the method that will handle the event triggered by an exception that is not handled by the application domain.

Enumeration	Description
enumeration AttributeTargets	Specifies the application elements on which it is valid to apply an attribute.
enumeration DayOfWeek	Specifies the day of the week.
enumeration LoaderOptimization	An enumeration used with the LoaderOptimizationAttribute class to specify loader optimizations for an executable.
enumeration TypeCode	Specifies the type of an object.
enumeration UriHostNameType	Defines host name types for the Uri.CheckHostName method.
enumeration UriPartial	Defines the parts of a URI for the Uri.GetLeftPart method.

• System.Object
• System.Activator
• System.AppDomainSetup --- System.IAppDomainSetup
• System.Array --- System.ICloneable, System.Collections.IList, System.Collections.ICollection, System.Collections.IEnumerable
• System.Attribute
• System.AttributeUsageAttribute
• System.CLSCompliantAttribute
• System.ContextStaticAttribute
• System.FlagsAttribute
• System.LoaderOptimizationAttribute
• System.NonSerializedAttribute
• System.ObsoleteAttribute
• System.ParamArrayAttribute
• System.SerializableAttribute
• System.ThreadStaticAttribute
• System.BitConverter
• System.Buffer
• System.CharEnumerator --- System.Collections.IEnumerator, System.ICloneable
• System.Console
• System.Convert
• System.DBNull --- System.Runtime.Serialization.ISerializable, System.IConvertible
• System.Delegate
• System.MulticastDelegate
• System.AssemblyLoadEventHandler
• System.AsyncCallback
• System.CrossAppDomainDelegate
• System.EventHandler
• System.ResolveEventHandler
• System.UnhandledExceptionEventHandler
• System.Environment
• System.EventArgs
• System.AssemblyLoadEventArgs
• System.ResolveEventArgs
• System.UnhandledExceptionEventArgs
• System.Exception
• System.ApplicationException
• System.SystemException
• System.AppDomainUnloadedException
• System.ArgumentException
• System.ArgumentNullException
• System.ArgumentOutOfRangeException
• System.DuplicateWaitObjectException
• System.ArithmeticException
• System.DivideByZeroException
• System.NotFiniteNumberException
• System.OverflowException
• System.ArrayTypeMismatchException
• System.BadImageFormatException
• System.CannotUnloadAppDomainException
• System.ContextMarshalException
• System.ExecutionEngineException
• System.FormatException
• System.UriFormatException
• System.IndexOutOfRangeException
• System.InvalidCastException
• System.InvalidOperationException
• System.ObjectDisposedException
• System.InvalidProgramException
• System.MemberAccessException
• System.FieldAccessException
• System.MethodAccessException
• System.MissingMemberException
• System.MissingFieldException
• System.MissingMethodException
• System.MulticastNotSupportedException
• System.NotImplementedException
• System.NotSupportedException
• System.PlatformNotSupportedException
• System.NullReferenceException
• System.OutOfMemoryException
• System.RankException
• System.StackOverflowException
• System.TypeInitializationException
• System.TypeLoadException
• System.DllNotFoundException
• System.EntryPointNotFoundException
• System.TypeUnloadedException
• System.UnauthorizedAccessException
• System.GC
• System.LocalDataStoreSlot
• System.MarshalByRefObject
• System.AppDomain --- System._AppDomain, System.Security.IEvidenceFactory
• System.ContextBoundObject
• System.Uri --- System.Runtime.Serialization.ISerializable
• System.Math
• System.Random
• System.Reflection.MemberInfo
• System.Type --- System.Reflection.IReflect
• System.String --- System.IComparable, System.ICloneable, System.IConvertible, System.Collections.IEnumerable
• System.TimeZone
• System.UriBuilder
• System.ValueType
• System.ArgIterator
• System.Boolean --- System.IComparable, System.IConvertible
• System.Byte --- System.IComparable, System.IFormattable, System.IConvertible
• System.Char --- System.IComparable, System.IConvertible
• System.DateTime --- System.IComparable, System.IFormattable, System.IConvertible
• System.Decimal --- System.IFormattable, System.IComparable, System.IConvertible
• System.Double --- System.IComparable, System.IFormattable, System.IConvertible
• System.Enum
• System.AttributeTargets
• System.DayOfWeek
• System.LoaderOptimization
• System.TypeCode
• System.UriHostNameType
• System.UriPartial
• System.Guid --- System.IFormattable, System.IComparable
• System.Int16 --- System.IComparable, System.IFormattable, System.IConvertible
• System.Int32 --- System.IComparable, System.IFormattable, System.IConvertible
• System.Int64 --- System.IComparable, System.IFormattable, System.IConvertible
• System.IntPtr --- System.Runtime.Serialization.ISerializable
• System.RuntimeArgumentHandle
• System.RuntimeFieldHandle --- System.Runtime.Serialization.ISerializable
• System.RuntimeMethodHandle --- System.Runtime.Serialization.ISerializable
• System.RuntimeTypeHandle --- System.Runtime.Serialization.ISerializable
• System.SByte --- System.IComparable, System.IFormattable, System.IConvertible
• System.Single --- System.IComparable, System.IFormattable, System.IConvertible
• System.TimeSpan --- System.IComparable
• System.TypedReference
• System.UInt16 --- System.IComparable, System.IFormattable, System.IConvertible
• System.UInt32 --- System.IComparable, System.IFormattable, System.IConvertible
• System.UInt64 --- System.IComparable, System.IFormattable, System.IConvertible
• System.UIntPtr --- System.Runtime.Serialization.ISerializable
• System.Void
• System.Version --- System.ICloneable, System.IComparable
• System.WeakReference --- System.Runtime.Serialization.ISerializable