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:

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

Additional Inherited Members

- Public Types inherited from Exiv2::BasicIo
enum  Position { beg, cur, end }
 Seek starting positions.
 
typedef std::auto_ptr< BasicIoAutoPtr
 BasicIo auto_ptr type.
 
- Public Attributes inherited from Exiv2::BasicIo
bytebigBlock_
 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.

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
dataPointer to data. Data must be at least size bytes long
sizeNumber 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
dataThe single byte to be written.
Returns
The value of the byte written if successful;
EOF if failure;

Implements Exiv2::BasicIo.

◆ read() [1/2]

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
rcountMaximum 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.

◆ read() [2/2]

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
bufPointer to a block of memory into which the read data is stored. The memory block must be at least rcount bytes long.
rcountMaximum 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.

◆ seek()

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

Move the current IO position.

Parameters
offsetNumber of bytes to move the IO position relative to the starting position specified by pos
posPosition 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
srcReference to another BasicIo instance. The entire contents of src are transferred to this object. The src object is invalidated by the method.
Exceptions
ErrorIn case of failure

Implements Exiv2::BasicIo.

◆ write() [1/2]

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
dataPointer to data. Data must be at least wcount bytes long
wcountNumber of bytes to be written.
Returns
Number of bytes written to the memory block successfully;
0 if failure;

Implements Exiv2::BasicIo.

◆ write() [2/2]

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
srcReference 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.


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