haiku/docs/user/storage/File.dox

/*
 * Copyright 2009-2012 Haiku, Inc. All rights reserved.
 * Distributed under the terms of the MIT License.
 *
 * Authors:
 *		Tyler Dauwalder
 *		John Scipione, jscipione@gmail.com
 *		Ingo Weinhold, bonefish@users.sf.net
 *
 * Corresponds to:
 *		headers/os/storage/File.h  hrev45060
 *		src/kits/storage/File.cpp  hrev45060
 */


/*!
	\file File.h
	Provides the BFile class.
*/


/*!
	\class BFile
	\ingroup storage
	\ingroup libbe
	\brief Provides the ability to read and write the data of a file.

	The file is automatically opened when you initialize a BFile and is 
	automatically closed when you re-initialize or destroy the object.

	Symbolic links are automatically transversed by opening a BFile.
	The node that the BFile ends up opening will be the file or directory
	that the link points to, not the symbolic link file itself.
*/


/*!
	\fn BFile::BFile()
	\brief Creates an uninitialized BFile object.

	Should be followed by a call to one of the SetTo() methods, or an
	assignment:
	- SetTo(const entry_ref* ref, uint32 openMode)
	- SetTo(const BEntry* entry, uint32 openMode)
	- SetTo(const char* path, uint32 openMode)
	- SetTo(const BDirectory* dir, const char* path, uint32 openMode)
	- operator=(const BFile &file)
*/


/*!
	\fn BFile::BFile(const BFile& file)
	\brief Creates a copy of the supplied BFile.

	If \a file is uninitialized, the newly constructed BFile will be too.

	\param file The BFile object to be copied.
*/


/*!
	\fn BFile::BFile(const entry_ref* ref, uint32 openMode)
	\brief Creates a BFile and initializes it to the file referred to by
		   the supplied entry_ref and according to the specified open mode.

	\param ref The entry_ref referring to the file.
	\param openMode The mode in which the file should be opened.

	\see SetTo(const entry_ref* ref, uint32 openMode)
*/


/*!
	\fn BFile::BFile(const BEntry* entry, uint32 openMode)
	\brief Creates a BFile and initializes it to the file referred to by
		   the supplied BEntry and according to the specified open mode.

	\param entry The BEntry referring to the file.
	\param openMode The mode in which the file should be opened.

	\see SetTo(const BEntry* entry, uint32 openMode)
*/


/*!
	\fn BFile::BFile(const char* path, uint32 openMode)
	\brief Creates a BFile and initializes it to the file referred to by
		   the supplied path name and according to the specified open mode.

	\param path The file's path name.
	\param openMode The mode in which the file should be opened.

	\see SetTo(const char* path, uint32 openMode)
*/


/*!
	\fn BFile::BFile(const BDirectory *dir, const char* path, uint32 openMode)
	\brief Creates a BFile and initializes it to the file referred to by
		   the supplied path name relative to the specified BDirectory and
		   according to the specified open mode.

	\param dir The BDirectory, relative to which the file's path name is
		   given.
	\param path The file's path name relative to \a dir.
	\param openMode The mode in which the file should be opened.

	\see SetTo(const BDirectory* dir, const char* path, uint32 openMode)
*/


/*!
	\fn BFile::~BFile()
	\brief Destroys the BFile object and frees all allocated resources.

	If the file is properly initialized, the file descriptor is closed.
*/


/*!
	\fn status_t BFile::SetTo(const entry_ref* ref, uint32 openMode)
	\brief Re-initializes the BFile to the file referred to by the
		   supplied entry_ref and according to the specified open mode.

	\param ref The entry_ref referring to the file.
	\param openMode The mode in which the file should be opened
		\a openMode must be a bitwise or of exactly one of the flags.
		- \c B_READ_ONLY: The file is opened read only.
		- \c B_WRITE_ONLY: The file is opened write only.
		- \c B_READ_WRITE: The file is opened for random read/write access.
		and any number of the flags
		- \c B_CREATE_FILE: A new file will be created, if it does not already
			exist.
		- \c B_FAIL_IF_EXISTS: If the file does already exist and
			\c B_CREATE_FILE is set, SetTo() fails.
		- \c B_ERASE_FILE: An already existing file is truncated to zero size.
		- \c B_OPEN_AT_END: Seek() to the end of the file after opening.

	\returns A status code.
	\retval B_OK Everything went fine.
	\retval B_BAD_VALUE \c NULL \a ref or bad \a openMode.
	\retval B_ENTRY_NOT_FOUND File not found or failed to create file.
	\retval B_FILE_EXISTS File exists and \c B_FAIL_IF_EXISTS was passed.
	\retval B_PERMISSION_DENIED File permissions didn't allow operation.
	\retval B_NO_MEMORY Insufficient memory for operation.
	\retval B_LINK_LIMIT Indicates a cyclic loop within the file system.
	\retval B_BUSY A node was busy.
	\retval B_FILE_ERROR A general file error.
	\retval B_NO_MORE_FDS The application has run out of file descriptors.
*/


/*!
	\fn status_t BFile::SetTo(const BEntry* entry, uint32 openMode)
	\brief Re-initializes the BFile to the file referred to by the
		   supplied BEntry and according to the specified open mode.

	\param entry the BEntry referring to the file
	\param openMode the mode in which the file should be opened

	\returns A status code.
	\retval B_OK Everything went fine.
	\retval B_BAD_VALUE \c NULL \a entry or bad \a openMode.
	\retval B_ENTRY_NOT_FOUND File not found or failed to create file.
	\retval B_FILE_EXISTS File exists and \c B_FAIL_IF_EXISTS was passed.
	\retval B_PERMISSION_DENIED File permissions didn't allow operation.
	\retval B_NO_MEMORY Insufficient memory for operation.
	\retval B_LINK_LIMIT Indicates a cyclic loop within the file system.
	\retval B_BUSY A node was busy.
	\retval B_FILE_ERROR A general file error.
	\retval B_NO_MORE_FDS The application has run out of file descriptors.

	\todo Implemented using SetTo(entry_ref*, uint32). Check, if necessary
		  to re-implement!
*/


/*!
	\fn status_t BFile::SetTo(const char* path, uint32 openMode)
	\brief Re-initializes the BFile to the file referred to by the
		   supplied path name and according to the specified open mode.

	\param path The file's path name.
	\param openMode The mode in which the file should be opened.

	\returns A status code.
	\retval B_OK Everything went fine.
	\retval B_BAD_VALUE \c NULL \a path or bad \a openMode.
	\retval B_ENTRY_NOT_FOUND File not found or failed to create file.
	\retval B_FILE_EXISTS File exists and \c B_FAIL_IF_EXISTS was passed.
	\retval B_PERMISSION_DENIED File permissions didn't allow operation.
	\retval B_NO_MEMORY Insufficient memory for operation.
	\retval B_LINK_LIMIT Indicates a cyclic loop within the file system.
	\retval B_BUSY A node was busy.
	\retval B_FILE_ERROR A general file error.
	\retval B_NO_MORE_FDS The application has run out of file descriptors.
*/
*/


/*!
	\fn status_t BFile::SetTo(const BDirectory* dir, const char* path,
		uint32 openMode)
	\brief Re-initializes the BFile to the file referred to by the
		   supplied path name relative to the specified BDirectory and
		   according to the specified open mode.

	\param dir The BDirectory, relative to which the file's path name is
		   given.
	\param path The file's path name relative to \a dir.
	\param openMode The mode in which the file should be opened.

	\returns A status code.
	\retval B_OK Everything went fine.
	\retval B_BAD_VALUE \c NULL \a dir or \a path or bad \a openMode.
	\retval B_ENTRY_NOT_FOUND File not found or failed to create file.
	\retval B_FILE_EXISTS File exists and \c B_FAIL_IF_EXISTS was passed.
	\retval B_PERMISSION_DENIED File permissions didn't allow operation.
	\retval B_NO_MEMORY Insufficient memory for operation.
	\retval B_LINK_LIMIT Indicates a cyclic loop within the file system.
	\retval B_BUSY A node was busy.
	\retval B_FILE_ERROR A general file error.
	\retval B_NO_MORE_FDS The application has run out of file descriptors.

	\todo Implemented using SetTo(BEntry*, uint32). Check, if necessary
		  to re-implement!
*/


/*!
	\fn bool BFile::IsReadable() const
	\brief Reports whether or not the file is readable.

	\return
	- \c true, if the BFile has been initialized properly and the file has
	  been been opened for reading,
	- \c false, otherwise.
*/


/*!
	\fn bool BFile::IsWritable() const
	\brief Reports whether or not the file is writable.

	\return
	- \c true, if the BFile has been initialized properly and the file has
	  been opened for writing,
	- \c false, otherwise.
*/


/*!
	ssize_t BFile::Read(void* buffer, size_t size)
	\brief Reads a number of bytes from the file into a buffer.

	\param buffer The buffer the data from the file shall be written to.
	\param size The number of bytes that shall be read.

	\returns The number of bytes read or an error code.
*/


/*!
	\fn ssize_t BFile::ReadAt(off_t location, void* buffer, size_t size)
	\brief Reads a number of bytes from a certain position within the file
		   into a buffer.

	\param location The position (in bytes) within the file from which the
		   data shall be read.
	\param buffer The buffer the data from the file shall be written to.
	\param size The number of bytes that shall be read.

	\returns The number of bytes read or an error code.
*/


/*!
	\fn ssize_t BFile::Write(const void* buffer, size_t size)
	\brief Writes a number of bytes from a buffer into the file.

	\param buffer The buffer containing the data to be written to the file.
	\param size The number of bytes that shall be written.

	\returns The number of bytes actually written or an error code.
*/


/*!
	\fn ssize_t BFile::WriteAt(off_t location, const void* buffer, size_t size)
	\brief \brief Writes a number of bytes from a buffer at a certain position
		   into the file.

	\param location The position (in bytes) within the file at which the data
		   shall be written.
	\param buffer The buffer containing the data to be written to the file.
	\param size The number of bytes that shall be written.

	\returns The number of bytes actually written or an error code.
*/


/*!
	\fn off_t BFile::Seek(off_t offset, uint32 seekMode)
	\brief Seeks to another read/write position within the file.

	It is allowed to seek past the end of the file. A subsequent call to
	Write() will pad the file with undefined data. Seeking before the
	beginning of the file will fail and the behavior of subsequent Read()
	or Write() invocations will be undefined.

	\param offset New read/write position, depending on \a seekMode relative
		   to the beginning or the end of the file or the current position.
	\param seekMode
		- \c SEEK_SET: move relative to the beginning of the file
		- \c SEEK_CUR: move relative to the current position
		- \c SEEK_END: move relative to the end of the file

	\returns The new read/write position relative to the beginning of the
		file or an error code.
	\retval B_ERROR Trying to seek before the beginning of the file.
	\retval B_FILE_ERROR The file is not properly initialized.
*/


/*!
	\fn off_t BFile::Position() const
	\brief Gets the current read/write position within the file.

	\returns The current read/write position relative to the beginning of the
		file or an error code.
	\retval B_ERROR After a Seek() before the beginning of the file.
	\retval B_FILE_ERROR The file has not been initialized.
*/


/*!
	\fn status_t BFile::SetSize(off_t size)
	\brief Sets the size of the file.

	If the file is shorter than \a size bytes it will be padded with
	unspecified data to the requested size. If it is larger, it will be
	truncated.

	\note There's no problem with setting the size of a BFile opened in
		  \c B_READ_ONLY mode, unless the file resides on a read only volume.

	\param size The new file size.

	\returns A status code.
	\retval B_OK Everything went fine.
	\retval B_NOT_ALLOWED Trying to set the size of a file on a read only
			volume.
	\retval B_DEVICE_FULL There's not enough space left on the volume.
*/


/*!
	\fn status_t BFile::GetSize(off_t* size) const
	\brief Gets the size of the file.

	\param size The file size to fill out.

	\returns A status code.

	\see BStatable::GetSize()
*/


/*!
	\fn BFile& BFile::operator=(const BFile &file)
	\brief Assigns another BFile to this BFile.

	If the other BFile is uninitialized, this one will be too. Otherwise it
	will refer to the same file using the same mode, unless an error occurs.

	\param file The original BFile to assign from.

	\returns A reference to the assigned BFile.
*/


/*!
	\fn int BFile::get_fd() const
	\brief Gets the file descriptor of the BFile.

	To be used instead of accessing the BNode's private \c fFd member directly.

	\returns The file descriptor, or -1 if not properly initialized.
*/


/*!
	\fn void BFile::close_fd()
	\brief Overrides BNode::close_fd() for binary compatibility with BeOS R5.
*/