Exiv2::MemIo

Exiv2::MemIo Class Reference

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:

Inheritance graph
[legend]

List of all members.

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.
 ~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.
virtual int close ()
 Does nothing on MemIo objects.
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.
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.
virtual int putb (byte data)
 Write one byte to the memory block. The IO position is advanced by one byte.
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.
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.
virtual int getb ()
 Read one byte from the memory block. The IO position is advanced by one byte.
virtual void transfer (BasicIo &src)
 Clear the memory block and then transfer data from the src BasicIo object into a new block of memory.
virtual int seek (long offset, Position pos)
 Move the current IO position.
virtual const byte * mmap ()
 Allow direct access to the underlying data buffer. The buffer is not protected against write access except for the const specifier.
virtual void munmap ()
 Remove a mapping established with mmap().
Accessors
virtual long tell () const
 Get the current IO position.
virtual long size () const
 Get the current memory buffer size in bytes.
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 reach the end, otherwise false.
virtual std::string path () const
 Returns a dummy path, indicating that memory access is used.
virtual BasicIo::AutoPtr temporary () const
 Returns a temporary data storage location. Currently returns an empty MemIo object, but callers should not rely on this behavior since it may change.

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.

Constructor & Destructor Documentation

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

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.

virtual int Exiv2::MemIo::close (  )  [virtual]

Does nothing on MemIo objects.

Returns:
0

Implements Exiv2::BasicIo.

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.

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.

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.

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.

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.

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.

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.

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.

virtual const byte* Exiv2::MemIo::mmap (  )  [inline, virtual]

Allow direct access to the underlying data buffer. The buffer is not protected against write access except for the const specifier.

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

Implements Exiv2::BasicIo.

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

Get the current IO position.

Returns:
Offset from the start of the memory block

Implements Exiv2::BasicIo.

virtual long 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.

virtual BasicIo::AutoPtr Exiv2::MemIo::temporary (  )  const [virtual]

Returns a temporary data storage location. Currently returns an empty MemIo object, but callers should not rely on this behavior since it may change.

Returns:
An instance of BasicIo

Implements Exiv2::BasicIo.

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