XPCOM API Reference

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1. Overview
2. Frozen Components
3. Frozen Functions
1. 3.1. Core Functions
2. 3.2. String Functions
4. Frozen Interfaces
1. 4.1. Core
2. 4.2. Files and Directories
3. 4.3. Streams
4. 4.4. Primitives
5. XPCOM "Glue" Classes and Functions
1. 5.1. Core
2. 5.2. String
3. 5.3. Thread Synchronization
6. Original Document Information

This page is the new home of the XPCOM Reference that we are migrating from here. If you are inclined to help with this migration, your help would be very much appreciated.

There may also be additional information located in Creating XPCOM Components Appendix B; it is unclear how much of the documentation in CXC overlaps with that from the to-be-migrated XPCOM reference mentioned in the last paragraph.

Please see the talk page for information about available templates and categories you should use when creating / editing pages.

Overview

This reference describes the frozen interfaces and functions provided by the XPCOM library. It also details the helper classes and functions provided by the XPCOM glue library. This reference is oriented toward extension authors and embedders of XPCOM.

NOTE: If you are working on a module in the Mozilla codebase that is compiled with MOZILLA_INTERNAL_API, then some of these APIs--the string functions and classes in particular--may differ significantly from what you should use. See the XPCOM string guide for documentation on the string API used internally within the Mozilla codebase.

Frozen Components

These components may be accessed using the XPCOM Component Manager or Service Manager.

nsCategoryManager: The XPCOM Category Manager.

nsDirectoryService: The XPCOM Directory Service.

nsLocalFile: A component implementing nsILocalFile .

nsObserverService: The XPCOM Observer Service.

nsScriptableInputStream: A component implementing nsIScriptableInputStream .

XPCOM primitive components: These components implement scriptable objects that "box" values of simple XPCOM types. They implement these interfaces: nsISupportsCString , nsISupportsChar , nsISupportsDouble , nsISupportsFloat , nsISupportsID , nsISupportsInterface , nsISupportsPRBool , nsISupportsPRInt16 , nsISupportsPRInt32 , nsISupportsPRInt64 , nsISupportsPRTime , nsISupportsPRUint16 , nsISupportsPRUint32 , nsISupportsPRUint64 , nsISupportsPRUint8 , nsISupportsString , and nsISupportsVoid .

Frozen Functions

These functions are exported from the XPCOM shared library.

Core Functions

NS_InitXPCOM2: The NS_InitXPCOM2 function initiates use of XPCOM in the calling process.

NS_InitXPCOM3: The NS_InitXPCOM3 function initiates use of XPCOM in the calling process with support for statically defined XPCOM modules.

NS_ShutdownXPCOM: The NS_ShutdownXPCOM function terminates use of XPCOM in the calling process.

NS_GetComponentManager: The NS_GetComponentManager function returns a reference to the XPCOM Component Manager.

NS_GetComponentRegistrar: The NS_GetComponentRegistrar function returns a reference to the XPCOM Component Registrar.

NS_GetServiceManager: The NS_GetServiceManager function returns a reference to the XPCOM Service Manager.

NS_GetMemoryManager: The NS_GetMemoryManager function returns a reference to the XPCOM Memory Manager.

NS_NewLocalFile: The NS_NewLocalFile function creates an instance of nsILocalFile that provides a platform independent representation of a file path.

NS_NewNativeLocalFile: The NS_NewNativeLocalFile function creates an instance of nsILocalFile that provides a platform independent representation of a file path. You should avoid using this function if you're not 100% certain that the full file path (not just a leaf) involved is always ASCII.

NS_Alloc: Allocates a block of memory using the XPCOM Memory Manager.

NS_Realloc: Reallocates a block of memory using the XPCOM Memory Manager.

NS_Free: Frees a block of memory using the XPCOM Memory Manager.

String Functions

These are the low-level "string" APIs provided by XPCOM as part of its frozen API. It is often better to use one of the string classes instead of using these functions directly.

NS_CStringContainerInit: The NS_CStringContainerInit function initializes a nsCStringContainer instance for use as a nsACString.

NS_CStringContainerInit2: The NS_CStringContainerInit2 function initializes a nsCStringContainer instance for use as a nsACString.

NS_CStringContainerFinish: The NS_CStringContainerFinish function releases any memory allocated by a nsCStringContainer instance.

NS_CStringGetData: The NS_CStringGetData function gives the caller read access to the string's internal buffer.

NS_CStringGetMutableData: The NS_CStringGetDataMutable function gives the caller write access to the string's internal buffer.

NS_CStringSetData: The NS_CStringSetData function copies data into the string's internal buffer.

NS_CStringSetDataRange: The NS_CStringSetDataRange function copies data into a section of the string's internal buffer.

NS_CStringCopy: The NS_CStringCopy function copies the value from one nsACString instance to another.

NS_CStringAppendData: The NS_CStringAppendData function appends data to the existing value of a nsACString instance.

NS_CStringInsertData: The NS_CStringInsertData function appends data to the existing value of a nsACString instance.

NS_CStringCutData: The NS_CStringCutData function removes a section of the string's internal buffer.

NS_CStringCloneData: The NS_CStringCloneData function returns a null-terminated, heap allocated copy of the string's internal buffer.

NS_StringContainerInit: The NS_StringContainerInit function initializes a nsStringContainer instance for use as a nsAString.

NS_StringContainerInit2: ...

NS_StringContainerFinish: The NS_StringContainerFinish function releases any memory allocated by a nsStringContainer instance.

NS_StringGetData: The NS_StringGetData function gives the caller access to the string's internal buffer.

NS_StringGetMutableData: ...

NS_StringSetData: The NS_StringSetData function copies data into the string's internal buffer.

NS_StringSetDataRange: The NS_StringSetDataRange function copies data into a section of the string's internal buffer.

NS_StringCopy: The NS_StringCopy function copies the value from one nsAString instance to another.

NS_StringAppendData: The NS_StringAppendData function appends data to the existing value of a nsAString instance.

NS_StringInsertData: The NS_StringInsertData function appends data to the existing value of a nsACString instance.

NS_StringCutData: The NS_StringCutData function removes a section of the string's internal buffer.

NS_StringCloneData: The NS_StringCloneData function returns a null-terminated, heap allocated copy of the string's internal buffer.

NS_CStringToUTF16: The NS_CStringToUTF16 function converts the value of a nsACString instance to UTF-16 and stores the result in a nsAString instance.

NS_UTF16ToCString: The NS_UTF16ToCString function converts the value of a nsAString instance from UTF-16 to the specified multi-byte encoding and stores the result in a nsACString instance.

Frozen Interfaces

Core

nsICategoryManager: The nsICategoryManager interface provides access to a data structure that holds a list of name-value pairs, called categories, where each value is a list of strings.

nsIClassInfo: The nsIClassInfo interface provides information about a specific implementation class.

nsIComponentManager: The nsIComponentManager interface provides methods to access factory objects and instantiate instances of classes.

nsIComponentRegistrar: The nsIComponentRegistrar interface provides methods to access and modify the XPCOM component registry.

nsIFactory: The nsIFactory interface allows for the creation of nsISupports derived classes without specifying a concrete class type.

nsIInterfaceRequestor: The nsIInterfaceRequestor interface defines a generic interface for requesting interfaces that a given object might provide access to.

nsIModule: The nsIModule interface must be implemented by each XPCOM component. It is the main entry point by which the system accesses an XPCOM component.

nsIMemory: The nsIMemory interface represents a generic memory allocator.

nsIObserver: The nsIObserver interface is a generic notification callback interface that is typically used in conjunction with nsIObserverService.

nsIObserverService: The nsIObserverService interface provides methods to add, remove, notify, and enumerate observers of various notifications.

nsIProgrammingLanguage: The nsIProgrammingLanguage interface provides an enumeration of programming language identifiers.

nsIProperties: The nsIProperties interface provides methods to access a map of named XPCOM object values.

nsIServiceManager: The nsIServiceManager manager interface provides a means to obtain global services in an application.

nsISimpleEnumerator: The nsISimpleEnumerator interface represents an enumeration of XPCOM objects and provides methods to access elements sequentially.

nsISupports: All XPCOM interfaces inherit the nsISupports interface.

nsISupportsWeakReference: The nsISupportsWeakReference interface is a factory interface, which produces appropriate instances of nsIWeakReference.

nsIWeakReference: The nsIWeakReference interface represents a proxy for an XPCOM object. It allows a consumer to hold an indirect, non-owning reference to an XPCOM object.

Files and Directories

nsIFile: The nsIFile interface represents a file or directory location in a platform-independent manner.

nsILocalFile: The nsILocalFile interface represents a file or directory location in a platform-independent manner that is accessible on the local filesystem. It extends nsIFile.

nsIDirectoryService: The nsIDirectoryService interface provides methods to initialize and configure a directory service instance.

nsIDirectoryServiceProvider: The nsIDirectoryServiceProvider interface is used by the Directory Service to get file locations.

nsIDirectoryServiceProvider2: The nsIDirectoryServiceProvider2 interface is used by the Directory Service to get an enumeration of file locations.

Streams

nsIInputStream: The nsIInputStream interface represents a readable data source.

nsIOutputStream: The nsIOutputStream interface represents a writable data sink.

nsIScriptableInputStream: The nsIScriptableInputStream interface provides scriptable access to a nsIInputStream instance.

Primitives

nsISupportsPrimitive: The nsISupportsPrimitive interface serves as a base interface for all of the nsISupports* family of interfaces.

nsISupportsPRBool: The nsISupportsPRBool interface provides scriptable access for boolean values.

nsISupportsChar: The nsISupportsChar interface provides scriptable access for single character values (often used to store an ASCII character).

nsISupportsPRInt16: The nsISupportsPRInt16 interface provides scriptable access for 16-bit signed integers.

nsISupportsPRInt32: The nsISupportsPRInt32 interface provides scriptable access for 32-bit signed integers.

nsISupportsPRInt64: The nsISupportsPRInt64 interface provides scriptable access for 64-bit signed integers.

nsISupportsPRUint16: The nsISupportsPRUint16 interface provides scriptable access for 16-bit unsigned integers.

nsISupportsPRUint32: The nsISupportsPRUint32 interface provides scriptable access for 32-bit unsigned integers.

nsISupportsPRUint64: The nsISupportsPRUint64 interface provides scriptable access for 64-bit unsigned integers.

nsISupportsPRUint8: The nsISupportsPRUint8 interface provides scriptable access for 8-bit unsigned integers.

nsISupportsDouble: The nsISupportsDouble interface provides scriptable access for double-precision floating-point values.

nsISupportsFloat: The nsISupportsFloat interface provides scriptable access for single-precision floating-point values.

nsISupportsPRTime: The nsISupportsPRTime interface provides scriptable access for PRTime values.

nsISupportsCString: The nsISupportsCString interface provides scriptable access for ASCII character strings.

nsISupportsString: The nsISupportsString interface provides scriptable access for Unicode character strings.

nsISupportsVoid: The nsISupportsVoid interface provides scriptable access for generic pointers. values.

nsISupportsID: The nsISupportsID interface provides scriptable access for boolean values.

nsISupportsInterfacePointer: The nsISupportsInterfacePointer interface provides scriptable access for XPCOM objects.

XPCOM "Glue" Classes and Functions

These classes and functions are provided to simplify the use of XPCOM from C++. They are not part of the frozen XPCOM API, which means that they may evolve over time. When these classes are used by a component, it may be necessary to link the component against the XPCOM glue library.

Core

nsCOMPtr: This utility class simplifies managing XPCOM interface references from C++ code.

nsMemory: The nsMemory class provides static helper routines to manage memory. These routines allow easy access to XPCOM's global nsIMemory implementation without having to go through the service manager to get it.

nsSupportsWeakReference: Inherit from this C++ class to add canonical support for nsISupportsWeakReference.

String

nsACString: The nsACString abstract class represents a character string composed of single-byte storage units. This class is typically used to represent ASCII or UTF-8 character arrays.

nsAString: The nsAString abstract class represents a character string composed of double-byte storage units. This class is typically used to represent Unicode character arrays.