Provides binary IO on blocks of memory by implementing the BasicIo interface. A copy-on-write implementation ensures that the data passed in is only copied when necessary, i.e., as soon as data is written to the MemIo. The original data is only used for reading. If writes are performed, the changed data can be retrieved using the read methods (since the data used in construction is never modified). More...

#include <basicio.hpp>

Inheritance diagram for Exiv2::MemIo:

[legend]

Public Member Functions
Creators
	MemIo ()
	Default constructor that results in an empty object.

	MemIo (const byte *data, long size)
	Constructor that accepts a block of memory. A copy-on-write algorithm allows read operations directly from the original data and will create a copy of the buffer on the first write operation. More...

virtual	~MemIo ()
	Destructor. Releases all managed memory.

Manipulators
virtual int	open ()
	Memory IO is always open for reading and writing. This method therefore only resets the IO position to the start. More...

virtual int	close ()
	Does nothing on MemIo objects. More...

virtual long	write (const byte *data, long wcount)
	Write data to the memory block. If needed, the size of the internal memory block is expanded. The IO position is advanced by the number of bytes written. More...

virtual long	write (BasicIo &src)
	Write data that is read from another BasicIo instance to the memory block. If needed, the size of the internal memory block is expanded. The IO position is advanced by the number of bytes written. More...

virtual int	putb (byte data)
	Write one byte to the memory block. The IO position is advanced by one byte. More...

virtual DataBuf	read (long rcount)
	Read data from the memory block. Reading starts at the current IO position and the position is advanced by the number of bytes read. More...

virtual long	read (byte *buf, long rcount)
	Read data from the memory block. Reading starts at the current IO position and the position is advanced by the number of bytes read. More...

virtual int	getb ()
	Read one byte from the memory block. The IO position is advanced by one byte. More...

virtual void	transfer (BasicIo &src)
	Clear the memory block and then transfer data from the src BasicIo object into a new block of memory. More...

virtual int	seek (long offset, Position pos)
	Move the current IO position. More...

virtual byte *	mmap (bool=false)
	Allow direct access to the underlying data buffer. The buffer is not protected against write access in any way, the argument is ignored. More...

virtual int	munmap ()
	Remove a mapping established with mmap(). If the mapped area is writeable, this ensures that changes are written back. More...

Public Member Functions inherited from Exiv2::BasicIo
virtual	~BasicIo ()
	Destructor.

Accessors
virtual long	tell () const
	Get the current IO position. More...

virtual size_t	size () const
	Get the current memory buffer size in bytes. More...

virtual bool	isopen () const
	Always returns true.

virtual int	error () const
	Always returns 0.

virtual bool	eof () const
	Returns true if the IO position has reached the end, otherwise false.

virtual std::string	path () const
	Returns a dummy path, indicating that memory access is used.

virtual void	populateFakeData ()
	Mark all the bNone blocks to bKnow. This avoids allocating memory for parts of the file that contain image-date (non-metadata/pixel data) More...

Additional Inherited Members
Public Types inherited from Exiv2::BasicIo
enum	Position { beg, cur, end }
	Seek starting positions.

typedef std::auto_ptr< BasicIo >	AutoPtr
	BasicIo auto_ptr type.

Public Attributes inherited from Exiv2::BasicIo
byte *	bigBlock_
	this is allocated and populated by mmap()

Protected Member Functions inherited from Exiv2::BasicIo
	BasicIo ()
	Default Constructor.

Detailed Description

Provides binary IO on blocks of memory by implementing the BasicIo interface. A copy-on-write implementation ensures that the data passed in is only copied when necessary, i.e., as soon as data is written to the MemIo. The original data is only used for reading. If writes are performed, the changed data can be retrieved using the read methods (since the data used in construction is never modified).

Note: If read only usage of this class is common, it might be worth creating a specialized readonly class or changing this one to have a readonly mode.

Examples: metacopy.cpp.

Constructor & Destructor Documentation

◆ MemIo()

Exiv2::MemIo::MemIo	(	const byte *	data,
		long	size
	)

Constructor that accepts a block of memory. A copy-on-write algorithm allows read operations directly from the original data and will create a copy of the buffer on the first write operation.

Parameters

data	Pointer to data. Data must be at least size bytes long
size	Number of bytes to copy.

Member Function Documentation

◆ close()

virtual int Exiv2::MemIo::close ( )

virtual

Does nothing on MemIo objects.

Returns: 0

Implements Exiv2::BasicIo.

◆ getb()

virtual int Exiv2::MemIo::getb ( )

virtual

Read one byte from the memory block. The IO position is advanced by one byte.

Returns: The byte read from the memory block if successful;
EOF if failure;

Implements Exiv2::BasicIo.

◆ mmap()

virtual byte* Exiv2::MemIo::mmap ( bool = false )

virtual

Allow direct access to the underlying data buffer. The buffer is not protected against write access in any way, the argument is ignored.

Note: The application must ensure that the memory pointed to by the returned pointer remains valid and allocated as long as the MemIo object exists.

Implements Exiv2::BasicIo.

◆ munmap()

virtual int Exiv2::MemIo::munmap ( )

virtual

Remove a mapping established with mmap(). If the mapped area is writeable, this ensures that changes are written back.

Returns: 0 if successful;
Nonzero if failure;

Implements Exiv2::BasicIo.

◆ open()

virtual int Exiv2::MemIo::open ( )

virtual

Memory IO is always open for reading and writing. This method therefore only resets the IO position to the start.

Returns: 0

Implements Exiv2::BasicIo.

◆ populateFakeData()

virtual void Exiv2::MemIo::populateFakeData ( )

virtual

Mark all the bNone blocks to bKnow. This avoids allocating memory for parts of the file that contain image-date (non-metadata/pixel data)

Note: This method should be only called after the concerned data (metadata) are all downloaded from the remote file to memory.

Reimplemented from Exiv2::BasicIo.

◆ putb()

virtual int Exiv2::MemIo::putb ( byte data )

virtual

Write one byte to the memory block. The IO position is advanced by one byte.

Parameters

data	The single byte to be written.

Returns: The value of the byte written if successful;
EOF if failure;

Implements Exiv2::BasicIo.

◆ read() [1/2]

virtual long Exiv2::MemIo::read	(	byte *	buf,
		long	rcount
	)

virtual

Read data from the memory block. Reading starts at the current IO position and the position is advanced by the number of bytes read.

Parameters

buf	Pointer to a block of memory into which the read data is stored. The memory block must be at least rcount bytes long.
rcount	Maximum number of bytes to read. Fewer bytes may be read if rcount bytes are not available.

Returns: Number of bytes read from the memory block successfully;
0 if failure;

Implements Exiv2::BasicIo.

◆ read() [2/2]

virtual DataBuf Exiv2::MemIo::read ( long rcount )

virtual

Read data from the memory block. Reading starts at the current IO position and the position is advanced by the number of bytes read.

Parameters

rcount Maximum number of bytes to read. Fewer bytes may be read if rcount bytes are not available.

Returns: DataBuf instance containing the bytes read. Use the DataBuf::size_ member to find the number of bytes read. DataBuf::size_ will be 0 on failure.

Implements Exiv2::BasicIo.

◆ seek()

virtual int Exiv2::MemIo::seek	(	long	offset,
		Position	pos
	)

virtual

Move the current IO position.

Parameters

offset	Number of bytes to move the IO position relative to the starting position specified by pos
pos	Position from which the seek should start

Returns: 0 if successful;
Nonzero if failure;

Implements Exiv2::BasicIo.

◆ size()

virtual size_t Exiv2::MemIo::size ( ) const

virtual

Get the current memory buffer size in bytes.

Returns: Size of the in memory data in bytes;
-1 if failure;

Implements Exiv2::BasicIo.

◆ tell()

virtual long Exiv2::MemIo::tell ( ) const

virtual

Get the current IO position.

Returns: Offset from the start of the memory block

Implements Exiv2::BasicIo.

◆ transfer()

virtual void Exiv2::MemIo::transfer ( BasicIo & src )

virtual

Clear the memory block and then transfer data from the src BasicIo object into a new block of memory.

This method is optimized to simply swap memory block if the source object is another MemIo instance. The source BasicIo instance is invalidated by this operation and should not be used after this method returns. This method exists primarily to be used with the BasicIo::temporary() method.

Parameters

src	Reference to another BasicIo instance. The entire contents of src are transferred to this object. The src object is invalidated by the method.

Exceptions

Error In case of failure

Implements Exiv2::BasicIo.

◆ write() [1/2]

virtual long Exiv2::MemIo::write ( BasicIo & src )

virtual

Write data that is read from another BasicIo instance to the memory block. If needed, the size of the internal memory block is expanded. The IO position is advanced by the number of bytes written.

Parameters

src	Reference to another BasicIo instance. Reading start at the source's current IO position

Returns: Number of bytes written to the memory block successfully;
0 if failure;

Implements Exiv2::BasicIo.

◆ write() [2/2]

virtual long Exiv2::MemIo::write	(	const byte *	data,
		long	wcount
	)

virtual

Write data to the memory block. If needed, the size of the internal memory block is expanded. The IO position is advanced by the number of bytes written.

Parameters

data	Pointer to data. Data must be at least wcount bytes long
wcount	Number of bytes to be written.

Returns: Number of bytes written to the memory block successfully;
0 if failure;

Implements Exiv2::BasicIo.

The documentation for this class was generated from the following file:

basicio.hpp

Public Member Functions

Accessors

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ MemIo()

Member Function Documentation

◆ close()

◆ getb()

◆ mmap()

◆ munmap()

◆ open()

◆ populateFakeData()

◆ putb()

◆ read() [1/2]

◆ read() [2/2]

◆ seek()

◆ size()

◆ tell()

◆ transfer()

◆ write() [1/2]

◆ write() [2/2]