# FileDescriptor An abstract handle to an input or output data resource, such as a file or a socket. ``` @frozen struct FileDescriptor ``` ## Overview You are responsible for managing the lifetime and validity of `FileDescriptor` values, in the same way as you manage a raw C file handle. ## Topics ### Creating a File Descriptor [`init(rawValue: CInt)`](/documentation/System/FileDescriptor/init(rawValue:)) Creates a strongly-typed file handle from a raw C file handle. [`let rawValue: CInt`](/documentation/System/FileDescriptor/rawValue) The raw C file handle. ### Opening a File [`open(_:_:options:permissions:retryOnInterrupt:)`](/documentation/System/FileDescriptor/open(_:_:options:permissions:retryOnInterrupt:)-4ql4b) [`open(_:_:options:permissions:retryOnInterrupt:)`](/documentation/System/FileDescriptor/open(_:_:options:permissions:retryOnInterrupt:)-5t3xn) [`struct AccessMode`](/documentation/System/FileDescriptor/AccessMode) The desired read and write access for a newly opened file. [`struct OpenOptions`](/documentation/System/FileDescriptor/OpenOptions) Options that specify behavior for a newly-opened file. ### Reading From a File [`func read(into: UnsafeMutableRawBufferPointer, retryOnInterrupt: Bool) throws -> Int`](/documentation/System/FileDescriptor/read(into:retryOnInterrupt:)) Reads bytes at the current file offset into a buffer. [`func read(fromAbsoluteOffset: Int64, into: UnsafeMutableRawBufferPointer, retryOnInterrupt: Bool) throws -> Int`](/documentation/System/FileDescriptor/read(fromAbsoluteOffset:into:retryOnInterrupt:)) Reads bytes at the specified offset into a buffer. ### Changing a File’s Offset [`func seek(offset: Int64, from: FileDescriptor.SeekOrigin) throws -> Int64`](/documentation/System/FileDescriptor/seek(offset:from:)) Repositions the offset for the given file descriptor. [`struct SeekOrigin`](/documentation/System/FileDescriptor/SeekOrigin) Options for specifying what a file descriptor’s offset is relative to. ### Writing To A File [`func write(UnsafeRawBufferPointer, retryOnInterrupt: Bool) throws -> Int`](/documentation/System/FileDescriptor/write(_:retryOnInterrupt:)) Writes the contents of a buffer at the current file offset. [`func write(toAbsoluteOffset: Int64, UnsafeRawBufferPointer, retryOnInterrupt: Bool) throws -> Int`](/documentation/System/FileDescriptor/write(toAbsoluteOffset:_:retryOnInterrupt:)) Writes the contents of a buffer at the specified offset. [`func writeAll(S) throws -> Int`](/documentation/System/FileDescriptor/writeAll(_:)) Writes a sequence of bytes to the current offset and then updates the offset. [`func writeAll(toAbsoluteOffset: Int64, S) throws -> Int`](/documentation/System/FileDescriptor/writeAll(toAbsoluteOffset:_:)) Writes a sequence of bytes to the given offset. ### Closing a File [`func close() throws`](/documentation/System/FileDescriptor/close()) Deletes a file descriptor. [`func closeAfter(() throws -> R) throws -> R`](/documentation/System/FileDescriptor/closeAfter(_:)) Runs a closure and then closes the file descriptor, even if an error occurs. ### Encoding File Descriptors ### Comparing File Descriptors ### Structures [`struct DuplicateOptions`](/documentation/System/FileDescriptor/DuplicateOptions) Options that specify behavior for a duplicated file descriptor. [`struct PipeOptions`](/documentation/System/FileDescriptor/PipeOptions) Options that specify behavior for a newly-created pipe. ### Instance Methods [`func duplicate(as: FileDescriptor, options: FileDescriptor.DuplicateOptions, retryOnInterrupt: Bool) throws(Errno) -> FileDescriptor`](/documentation/System/FileDescriptor/duplicate(as:options:retryOnInterrupt:)) Duplicates this file descriptor and returns the newly created copy. [`func duplicate(as: FileDescriptor?, retryOnInterrupt: Bool) throws -> FileDescriptor`](/documentation/System/FileDescriptor/duplicate(as:retryOnInterrupt:)) Duplicates this file descriptor and returns the newly created copy. [`func resize(to: Int64, retryOnInterrupt: Bool) throws`](/documentation/System/FileDescriptor/resize(to:retryOnInterrupt:)) Truncates or extends the file referenced by this file descriptor. [`func stat(retryOnInterrupt: Bool) throws(Errno) -> Stat`](/documentation/System/FileDescriptor/stat(retryOnInterrupt:)) Creates a `Stat` struct for the file referenced by this `FileDescriptor`. ### Type Properties [`static var standardError: FileDescriptor`](/documentation/System/FileDescriptor/standardError) The standard error file descriptor, with a numeric value of 2. [`static var standardInput: FileDescriptor`](/documentation/System/FileDescriptor/standardInput) The standard input file descriptor, with a numeric value of 0. [`static var standardOutput: FileDescriptor`](/documentation/System/FileDescriptor/standardOutput) The standard output file descriptor, with a numeric value of 1. ### Type Methods [`static func pipe() throws -> (readEnd: FileDescriptor, writeEnd: FileDescriptor)`](/documentation/System/FileDescriptor/pipe()) Creates a unidirectional data channel, which can be used for interprocess communication. [`static func pipe(options: FileDescriptor.PipeOptions) throws(Errno) -> (readEnd: FileDescriptor, writeEnd: FileDescriptor)`](/documentation/System/FileDescriptor/pipe(options:)) Creates a unidirectional data channel, which can be used for interprocess communication. ## Relationships ### Conforms To [`Decodable`](/documentation/Swift/Decodable) [`Equatable`](/documentation/Swift/Equatable) [`Encodable`](/documentation/Swift/Encodable) [`BitwiseCopyable`](/documentation/Swift/BitwiseCopyable) [`Sendable`](/documentation/Swift/Sendable) [`Hashable`](/documentation/Swift/Hashable) [`RawRepresentable`](/documentation/Swift/RawRepresentable) [`SendableMetatype`](/documentation/Swift/SendableMetatype) [`Copyable`](/documentation/Swift/Copyable) --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)