BMallocIO Class Reference

A BPositionIO derived class that creates a memory buffer. More...

Inherits BPositionIO.

Public Member Functions
	BMallocIO ()
	Create a new memory buffer with block size 256.
virtual	~BMallocIO ()
	Destroy the object and free the internal buffer.
const void *	Buffer () const
	Return a pointer to the internal buffer.
size_t	BufferLength () const
	Return the number of bytes in the buffer.
virtual off_t	Position () const
	Return the position of the cursor.
virtual ssize_t	ReadAt (off_t position, void *buffer, size_t size)
	Read data at a certain position.
virtual off_t	Seek (off_t position, uint32 seekMode)
	Move the cursor to a given position.
void	SetBlockSize (size_t blockSize)
	Change the block size to a certain value.
virtual status_t	SetSize (off_t size)
	Change the size of the buffer.
virtual ssize_t	WriteAt (off_t position, const void *buffer, size_t size)
	Write data to a certain position.
Public Member Functions inherited from BPositionIO
	BPositionIO ()
	This constructor does nothing.
virtual	~BPositionIO ()
	This destructor does nothing.
virtual status_t	GetSize (off_t *size) const
	Get the size of the object or data.
virtual off_t	Position () const =0
	Pure virtual to return the current position of the cursor.
virtual ssize_t	Read (void *buffer, size_t size)
	Read data from current position.
virtual ssize_t	ReadAt (off_t position, void *buffer, size_t size)=0
	Pure virtual to read data from a certain position.
status_t	ReadAtExactly (off_t position, void *buffer, size_t size, size_t *_bytesRead=NULL)
	Reads an exact amount of data from the object at the specified position into a buffer.
virtual off_t	Seek (off_t position, uint32 seekMode)=0
	Pure virtual to move the cursor to a certain position.
virtual status_t	SetSize (off_t size)
	Set the size of the object or data.
virtual ssize_t	Write (const void *buffer, size_t size)
	Write data to the current position.
virtual ssize_t	WriteAt (off_t position, const void *buffer, size_t size)=0
	Pure virtual to write data to a certain position.
status_t	WriteAtExactly (off_t position, const void *buffer, size_t size, size_t *_bytesWritten=NULL)
	Writes an exact amount of data from a buffer to the object at the specified position.
Public Member Functions inherited from BDataIO
	BDataIO ()
	This constructor does nothing.
virtual	~BDataIO ()
	This destructor does nothing.
virtual status_t	Flush ()
	Writes pending data to underlying storage.
virtual ssize_t	Read (void *buffer, size_t size)
	Reads data from the object into a buffer.
status_t	ReadExactly (void *buffer, size_t size, size_t *_bytesRead=NULL)
	Reads an exact amount of data from the object into a buffer.
virtual ssize_t	Write (const void *buffer, size_t size)
	Writes data from a buffer to the object.
status_t	WriteExactly (const void *buffer, size_t size, size_t *_bytesWritten=NULL)
	Writes an exact amount of data from a buffer to the object.

Detailed Description

A BPositionIO derived class that creates a memory buffer.

This class creates a memory buffer and provides a BPositionIO interface to work on it. The memory buffer grows and shrinks automatically. This is especially useful if you want to use a method or function that works on an object derived from BPositionIO and you want to do something with the resulting data, or it could be useful if you want to read and write to memory in a safe way, since this class has boundary checking.

BMallocIO allocates a buffer based on a certain block size. This provides a mechanism that will prevent it from needing to allocate new memory too often. The default block size is 256 bytes, you can change it with SetBlockSize(). If you are sure you are going to use a bigger buffer, change the block size so that you won't have to allocate more memory too often, especially if you use this class in performance-critical code.

If you require a BPositionIO derived object that works on buffers you provide, have a look at BMemoryIO.

Since

BeOS R3

Constructor & Destructor Documentation

BMallocIO()

BMallocIO::BMallocIO

(

)

Create a new memory buffer with block size 256.

See also

SetBlockSize()

Since

BeOS R3

~BMallocIO()

BMallocIO::~BMallocIO ( )

virtual

Destroy the object and free the internal buffer.

Since

BeOS R3

Member Function Documentation

Buffer()

const void * BMallocIO::Buffer

(

)

const

Return a pointer to the internal buffer.

As with any pointer to internal buffers the Haiku API exposes, make sure you don't change anything since it doesn't belong to you.

Since

BeOS R3

BufferLength()

size_t BMallocIO::BufferLength

(

)

const

Return the number of bytes in the buffer.

This number doesn't have to be the same size as the buffer is. Because memory is allocated in blocks the actual size of the buffer may be greater, but this method only returns the number of bytes that are actually used.

Since

BeOS R3

Position()

off_t BMallocIO::Position ( ) const

virtual

Return the position of the cursor.

Since

BeOS R3

Implements BPositionIO.

ReadAt()

ssize_t BMallocIO::ReadAt ( off_t  pos, void *  buffer, size_t  size  )

virtual

Read data at a certain position.

Parameters

[in]	pos	Offset into the data where to read from.
[out]	buffer	The buffer to copy the read bytes in.
[in]	size	Size of the buffer.

Returns

The number of read bytes, or B_BAD_VALUE if the provided buffer is invalid.

Since

BeOS R3

Implements BPositionIO.

Seek()

off_t BMallocIO::Seek ( off_t  position, uint32  seekMode  )

virtual

Move the cursor to a given position.

Parameters

position	The position to move the cursor to.
seekMode	The mode determines where the cursor is placed. Possibilities: SEEK_SET The cursor is set to position. SEEK_CUR The position is added to the current position of the cursor. SEEK_END The cursor is put at the end of the data, plus position added to it.

Returns

The new position as an off_t.

Since

BeOS R3

Implements BPositionIO.

SetBlockSize()

void BMallocIO::SetBlockSize

(

size_t

blockSize

)

Change the block size to a certain value.

This class allocates memory in blocks. If you are in performance-critical code you might want to tweak this setting to create a better performance in case you know you are going to allocate more than the default block size of 256.

Parameters

blockSize

The new block size.

Since

BeOS R3

SetSize()

status_t BMallocIO::SetSize ( off_t  size )

virtual

Change the size of the buffer.

This method changes the size of the current buffer. If size is smaller than the current size, the data will be cleared.

Parameters

size	The new size of the buffer.

Returns

A status code.

Return values

B_OK	Resizing the data succeeded.
B_NO_MEMORY	Failed to allocate the necessary memory.

Since

BeOS R3

Reimplemented from BPositionIO.

WriteAt()

ssize_t BMallocIO::WriteAt ( off_t  pos, const void *  buffer, size_t  size  )

virtual

Write data to a certain position.

Parameters

pos	Offset into the data where to write to.
buffer	The buffer to copy from.
size	The size of the buffer.

Returns

The number of bytes written or B_BAD_VALUE if the provided. buffer is invalid.

Since

BeOS R3

Implements BPositionIO.