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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.

Namespace hierarchy

Classes

Class Description
Activator Contains methods to create types of objects locally or remotely, or obtain references to existing remote objects.
AppDomain Represents an application domain, which is an isolated environment where applications execute. This class cannot be inherited.
AppDomainSetup Represents assembly binding information that can be added to an instance of AppDomain.
AppDomainUnloadedException The exception that is thrown when an attempt is made to access an unloaded application domain.
ApplicationException The exception that is thrown when a non-fatal application error occurs.
ArgumentException The exception that is thrown when one of the arguments provided to a method is not valid.
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.
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.
ArithmeticException The exception that is thrown for errors in an arithmetic, casting, or conversion operation.
Array Provides methods for creating, manipulating, searching, and sorting arrays, thereby serving as the base class for all arrays in the common language runtime.
ArrayTypeMismatchException The exception that is thrown when an attempt is made to store an element of the wrong type within an array.
AssemblyLoadEventArgs Provides data for the AssemblyLoad event.
Attribute Base class for custom attributes.
AttributeUsageAttribute Specifies the usage of another attribute class. This class cannot be inherited.
BadImageFormatException The exception that is thrown when the file image of a DLL or an executable program is invalid.
BitConverter Converts base data types to an array of bytes, and an array of bytes to base data types.
Buffer Manipulates arrays of primitive types.
CannotUnloadAppDomainException The exception that is thrown when an attempt to unload an application domain fails.
CharEnumerator Supports iterating over a String and reading its individual characters.
CLSCompliantAttribute Indicates whether a program element is compliant with the Common Language Specification (CLS). This class cannot be inherited.
Console Represents the standard input, output, and error streams for console applications. This class cannot be inherited.
ContextBoundObject Defines the base class for all context-bound classes.
ContextMarshalException The exception that is thrown when an attempt to marshal an object across a context boundary fails.
ContextStaticAttribute Indicates that the value of a static field is unique for a particular context.
Convert Converts a base data type to another base data type.
DBNull Represents a null value.
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.
DivideByZeroException The exception that is thrown when there is an attempt to divide an integral or decimal value by zero.
DllNotFoundException The exception that is thrown when a DLL specified in a DLL import cannot be found.
DuplicateWaitObjectException The exception that is thrown when an object appears more than once in an array of synchronization objects.
EntryPointNotFoundException The exception that is thrown when an attempt to load a class fails due to the absence of an entry method.
Enum Provides the base class for enumerations.
Environment Provides information about, and means to manipulate, the current environment and platform. This class cannot be inherited.
EventArgs EventArgs is the base class for classes containing event data.
Exception Represents errors that occur during application execution.
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.
FieldAccessException The exception that is thrown when there is an invalid attempt to access a private or protected field inside a class.
FlagsAttribute Indicates that an enumeration can be treated as a bit field; that is, a set of flags.
FormatException The exception that is thrown when the format of an argument does not meet the parameter specifications of the invoked method.
GC Controls the system garbage collector, a service that automatically reclaims unused memory.
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.
InvalidCastException The exception that is thrown for invalid casting or explicit conversion.
InvalidOperationException The exception that is thrown when a method call is invalid for the object's current state.
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.
LoaderOptimizationAttribute Used to set the default loader optimization policy for the main method of an executable application.
LocalDataStoreSlot Encapsulates a memory slot to store local data. This class cannot be inherited.
MarshalByRefObject Enables access to objects across application domain boundaries in applications that support remoting.
Math Provides constants and static methods for trigonometric, logarithmic, and other common mathematical functions.
MemberAccessException The exception that is thrown when an attempt to access a class member fails.
MethodAccessException The exception that is thrown when there is an invalid attempt to access a private or protected method inside a class.
MissingFieldException The exception that is thrown when there is an attempt to dynamically access a field that does not exist.
MissingMemberException The exception that is thrown when there is an attempt to dynamically access a class member that does not exist.
MissingMethodException The exception that is thrown when there is an attempt to dynamically access a method that does not exist.
MTAThreadAttribute Indicates that the COM threading model for an application is multithreaded apartment (MTA).
MulticastDelegate Represents a multicast delegate; that is, a delegate that can have more than one element in its invocation list.
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 (Nothing in Visual Basic). This class cannot be inherited.
NonSerializedAttribute Indicates that a field of a serializable class should not be serialized. This class cannot be inherited.
NotFiniteNumberException The exception that is thrown when a floating-point value is positive infinity, negative infinity, or Not-a-Number (NaN).
NotImplementedException The exception that is thrown when a requested method or operation is not implemented.
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.
NullReferenceException The exception that is thrown when there is an attempt to dereference a null object reference.
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.
ObjectDisposedException The exception that is thrown when an operation is performed on a disposed object.
ObsoleteAttribute Marks the program elements that are no longer in use. This class cannot be inherited.
OperatingSystem Represents information about an operating system, such as the version and platform identifier.
OutOfMemoryException The exception that is thrown when there is not enough memory to continue the execution of a program.
OverflowException The exception that is thrown when an arithmetic, casting, or conversion operation in a checked context results in an overflow.
ParamArrayAttribute Indicates that the method will allow a variable number of arguments in its invocation. This class cannot be inherited.
PlatformNotSupportedException The exception that is thrown when a feature does not run on a particular platform.
Random Represents a pseudo-random number generator, a device that produces a sequence of numbers that meet certain statistical requirements for randomness.
RankException The exception that is thrown when an array with the wrong number of dimensions is passed to a method.
ResolveEventArgs Provides data for the TypeResolve, ResourceResolve, and AssemblyResolve events.
SerializableAttribute Indicates that a class can be serialized. This class cannot be inherited.
StackOverflowException The exception that is thrown when the execution stack overflows by having too many pending method calls. This class cannot be inherited.
STAThreadAttribute Indicates that the COM threading model for an application is single-threaded apartment (STA).
String Represents text; that is, a series of Unicode characters.
SystemException Defines the base class for predefined exceptions in the System namespace.
ThreadStaticAttribute Indicates that the value of a static field is unique for each thread.
TimeZone Represents a time zone.
Type Represents type declarations: class types, interface types, array types, value types, and enumeration types.
TypeInitializationException The exception that is thrown as a wrapper around the exception thrown by the class initializer. This class cannot be inherited.
TypeLoadException The exception that is thrown when type-loading failures occur.
TypeUnloadedException The exception that is thrown when there is an attempt to access an unloaded 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.
UnhandledExceptionEventArgs Provides data for the event that is raised when there is an exception that is not handled by the application domain.
Uri Provides an object representation of a uniform resource identifier (URI) and easy access to the parts of the URI.
UriBuilder Provides a custom constructor for uniform resource indentifiers (URIs) and modifies URIs for the Uri class.
UriFormatException The exception that is thrown when an invalid Uniform Resource Identifier (URI) is detected.
ValueType Provides the base class for value types.
Version Represents the version number for a common language runtime assembly. This class cannot be inherited.
WeakReference Represents a weak reference, which references an object while still allowing it to be garbage collected.

Interfaces

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

Structures

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

Delegates

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

Enumerations

Enumeration Description
AttributeTargets Specifies the application elements on which it is valid to apply an attribute.
DayOfWeek Specifies the day of the week.
Environment.SpecialFolder Specifies enumerated constants used to retrieve directory paths to system special folders.
LoaderOptimization An enumeration used with the LoaderOptimizationAttribute class to specify loader optimizations for an executable.
PlatformID Describes the platforms supported by an assembly.
TypeCode Specifies the type of an object.
UriHostNameType Defines host name types for the Uri.CheckHostName method.
UriPartial Defines the parts of a URI for the Uri.GetLeftPart method.

See Also

.NET Framework Class Library

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