RWDBBlob Class Reference
[Data Types]

Stores Binary Large Objects (Blobs) and includes relevant accessors. More...

#include <rw/db/blob.h>

Inheritance diagram for RWDBBlob:

List of all members.

Public Member Functions
virtual RWCollectable *	newSpecies () const
virtual RWClassID	isA () const
	RWDBBlob ()
	RWDBBlob (size_t size)
	RWDBBlob (void *data, size_t length)
	RWDBBlob (const RWDBBlob &blob)
RWDBBlob &	operator= (const RWDBBlob &blob)
void	clear (size_t size=0)
void	getBytes (void *buffer, size_t size, size_t offset=0) const
void	putBytes (const void *buffer, size_t size, size_t offset=0, size_t resize=256)
size_t	length () const
size_t	capacity () const
unsigned char *	data () const
virtual RWspace	binaryStoreSize () const
virtual int	compareTo (const RWCollectable *c) const
virtual bool	isEqual (const RWCollectable *c) const
virtual unsigned	hash () const
virtual void	saveGuts (RWFile &file) const
virtual void	saveGuts (RWvostream &stream) const
virtual void	restoreGuts (RWFile &file)
virtual void	restoreGuts (RWvistream &stream)
void	acquire () const
void	release () const
Static Public Member Functions
static RWClassID	classIsA ()

---

Detailed Description

Most database vendors supply one or more data types that can store binary data of any length. These data types are commonly known as Binary Large Objects or Blobs. The DB Interface Module stores data of these types as RWDBBlob. Class RWDBBlob provides storage and rudimentary access to the binary data. Applications may want to derive from RWDBBlob to add semantics to the data.

This class is implemented using a technique called copy on write. With this technique, the copy constructor and assignment operators still reference the old object and hence are very fast. An actual copy is made only when a write is performed, that is, if the object is about to be changed. The net result is excellent performance, but with easy-to-understand value semantics.

The member function putBytes() is used to populate an RWDBBlob. This method is safe and robust, but can be inconvenient in cases where large objects have already been loaded into memory. The constructor RWDBBlob(void* data, size_t length) is provided to allow applications to wrap existing data blocks in an RWDBBlob interface. Blobs built with this constructor do not manage the memory addressed by the data pointer; your application continues to be responsible for it.

RWDBBlob inherits from class RWCollectable. The virtual functions of the base class RWCollectable have been redefined.

Synopsis

 #include <rw/db/blob.h>

 RWDBBlob b;          // default; zero capacity and length
 RWDBBlob b(2048);
 RWDBBlob b((void*)&myGif.data(),myGif.size());

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Constructor & Destructor Documentation

RWDBBlob::RWDBBlob

(

)

Default constructor. Creates a blob with zero capacity and length.

RWDBBlob::RWDBBlob

(

size_t

size

)

Creates a blob that has an initial capacity to store size bytes of binary data. The length is set to zero.

RWDBBlob::RWDBBlob	(	void *	data,
		size_t	length
	)

Creates a blob using the data block provided. The caller retains ownership of the data, and is responsible for providing an accurate length, for ensuring that the data pointer is valid for the lifetime of the blob, and for deallocation of the data, if necessary.

RWDBBlob::RWDBBlob

(

const RWDBBlob &

blob

)

Copy constructor. The created blob shares data with blob until the data is modified.

---

Member Function Documentation

void RWDBBlob::acquire

(

)

const

Attempts to acquire the internal mutex lock. If the mutex is already locked by another thread, the function blocks until the mutex is released. This function can be called from a const object.

Note:

In single-threaded builds, this function evaluates to a no-op.

virtual RWspace RWDBBlob::binaryStoreSize

(

)

const [virtual]

Returns the number of bytes needed to store self.

Reimplemented from RWCollectable.

size_t RWDBBlob::capacity

(

)

const

Returns the current capacity of self in bytes. This is the number of bytes self can hold without resizing.

static RWClassID RWDBBlob::classIsA

(

)

[static]

Returns the RWClassID of this class.

Reimplemented from RWCollectable.

void RWDBBlob::clear

(

size_t

size = 0

)

Sets self's data length to 0 and capacity to size. If the current capacity is not equal to size, reallocates memory to adjust self's capacity to size. To avoid reallocation of memory, pass the current capacity as size.

virtual int RWDBBlob::compareTo

(

const RWCollectable *

c

)

const [virtual]

Returns 0, if self and c share data; returns 1, if self has length greater than c; returns -1, if c has length greater than self, or if c is not an RWDBBlob via the isA() method. Otherwise, returns an integer less than, greater than, or equal to zero, depending upon whether self's data is less than, greater than, or equal to the data of c, according to the semantics of the standard C library function memcmp().

Reimplemented from RWCollectable.

unsigned char* RWDBBlob::data

(

)

const

Provides access to the blob's data as a pointer to the data storage. The data storage is owned by the RWDBBlob and may not be changed or deleted. If the data must be manipulated, the application should derive from RWDBBlob to gain access to the protected data storage and controls.

void RWDBBlob::getBytes	(	void *	buffer,
		size_t	size,
		size_t	offset = 0
	)			const

Copies size bytes, starting at self's offset to buffer. The buffer is assumed to be large enough to contain the bytes. Failure to provide a large enough buffer results in a memory overwrite, which may have unpredictable results.

virtual unsigned RWDBBlob::hash

(

)

const [virtual]

Returns a hash value for use in collection classes.

Reimplemented from RWCollectable.

virtual RWClassID RWDBBlob::isA

(

)

const [virtual]

Returns __RWDBBLOB.

Reimplemented from RWCollectable.

virtual bool RWDBBlob::isEqual

(

const RWCollectable *

c

)

const [virtual]

Returns true if self and c are byte for byte the same. Calls compareTo() to perform the comparison.

Reimplemented from RWCollectable.

size_t RWDBBlob::length

(

)

const

Returns the current length of self's data in bytes.

virtual RWCollectable* RWDBBlob::newSpecies

(

)

const [virtual]

Allocates a new object off the heap of the same type as self and returns a pointer to it. You are responsible for deleting the object when done with it.

Reimplemented from RWCollectable.

RWDBBlob& RWDBBlob::operator=

(

const RWDBBlob &

blob

)

Assignment operator. Self shares data with blob until the data is modified. Returns a reference to self.

void RWDBBlob::putBytes	(	const void *	buffer,
		size_t	size,
		size_t	offset = 0,
		size_t	resize = 256
	)

Copies size bytes from buffer into self, starting at self's offset. Exactly size bytes are copied, and therefore buffer is assumed to contain at least size bytes. Self's capacity is enlarged by multiples of resize bytes if the existing capacity is insufficient.

void RWDBBlob::release

(

)

const

Releases a previously acquired mutex. This function can be called from a const object.

Note:

In single-threaded builds, this function evaluates to a no-op.

virtual void RWDBBlob::restoreGuts

(

RWvistream &

stream

)

[virtual]

Reads stream, replacing the contents of self.

Reimplemented from RWCollectable.

virtual void RWDBBlob::restoreGuts

(

RWFile &

file

)

[virtual]

Reads file, replacing the contents of self.

Reimplemented from RWCollectable.

virtual void RWDBBlob::saveGuts

(

RWvostream &

stream

)

const [virtual]

Writes the contents of self to stream.

Reimplemented from RWCollectable.

virtual void RWDBBlob::saveGuts

(

RWFile &

file

)

const [virtual]

Writes the contents of self to file.

Reimplemented from RWCollectable.