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Oracle® C++ Call Interface Programmer's Guide,
11g Release 1 (11.1)

B28390-07
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Blob Class

The Blob class defines the common properties of objects of type BLOB. A BLOB is a large binary object stored as a column value in a row of a database table. A Blob object contains a logical pointer to a BLOB, not the BLOB itself.

Methods of the Blob class enable you to perform specific tasks related to Blob objects.

Methods of the ResultSet and Statement classes, such as getBlob() and setBlob(), enable you to access an SQL BLOB value.

The only methods valid on a NULL Blob object are setName(), isNull(), and operator=().

An uninitialized Blob object can be initialized by:

See Also:

Table 13-8 Summary of Blob Methods

Method Summary

Blob()

Blob class constructor.

append()

Appends a specified BLOB to the end of the current BLOB.

close()

Closes a previously opened BLOB.

closeStream()

Closes the Stream object obtained from the BLOB.

copy()

Copies a specified portion of a BFILE or BLOB into the current BLOB.

getChunkSize()

Returns the smallest data size to perform efficient writes to the BLOB.

 

getOptions()

Returns the BLOB's LobOptionValue for a specified LobOptionType.

getStream()

Returns data from the BLOB as a Stream object.

isInitialized()

Tests whether the Blob object is initialized

isNull()

Tests whether the Blob object is atomically NULL.

isOpen()

Tests whether the BLOB is open.

length()

Returns the number of bytes in the BLOB.

open()

Opens the BLOB with read or read/write access.

operator=()

Assigns a BLOB locator to the Blob object.

operator==()

Tests whether two Blob objects are equal.

operator!= ()

Tests whether two Blob objects are not equal.

read()

Reads a portion of the BLOB into a buffer.

setEmpty()

Sets the Blob object to empty.

setNull()

Sets the Blob object to atomically NULL.

setOptions()

Specifies a LobOptionValue for a particular LobOptionType. Enables advanced compression, encryption and deduplication of BLOBs.

trim()

Truncates the BLOB to a specified length.

write()

Writes a buffer into an unopened BLOB.

writeChunk()

Writes a buffer into an open BLOB.



Blob()

Blob class constructor.

Syntax Description
Blob();
Creates a NULL Blob object.
Blob(
   const Connection *connectionp);
Creates an uninitialized Blob object.
Blob(
   const Blob &srcBlob);
Creates a copy of a Blob object.

Parameter Description
connectionp
The connection pointer
srcBlob
The source Blob object.


append()

Appends a BLOB to the end of the current BLOB.

Syntax

void append(
   const Blob &srcBlob);
Parameter Description
srcBlob
The BLOB object to be appended to the current BLOB object.


close()

Closes a BLOB.

Syntax

void close();

closeStream()

Closes the Stream object obtained from the BLOB.

Syntax

void closeStream(
   Stream *stream);
Parameter Description
stream
The Stream to be closed.


copy()

Copies a part or all of a BFILE or BLOB into the current BLOB.

Syntax Description
void copy(
   const Bfile &srcBfile,
   unsigned int numBytes,
   unsigned int dstOffset = 1,
   unsigned int srcOffset = 1);
Copies a part of a BFILE into the current BLOB.
void copy(
   const Blob &srcBlob,
   unsigned int numBytes,
   unsigned int dstOffset = 1,
   unsigned int srcOffset = 1);
Copies a part of a BLOB into the current BLOB.

If the destination BLOB has deduplication enabled, and the source and destination BLOBs are in the same column, the new BLOB will be created as copy-on-write. All other settings are inherited from the source BLOB. If the destination BLOB has deduplication disabled, it will be a completely new copy of the BLOB.


Parameter Description
srcBfile
The BFILE from which the data is to be copied.
srcBlob
The BLOB from which the data is to be copied.
numBytes
The number of bytes to be copied from the source BFILE or BLOB. Valid values are numbers greater than 0.
dstOffset
The starting position at which to begin writing data into the current BLOB. Valid values are numbers greater than or equal to 1.
srcOffset
The starting position at which to begin reading data from the source BFILE or BLOB. Valid values are numbers greater than or equal to 1.


getChunkSize()

Returns the smallest data size to perform efficient writes to the BLOB.

Syntax

unsigned int getChunkSize() const;

getOptions()

Returns the BLOB's LobOptionValue for a specified LobOptionType.

Will throw an exception if attempting to retrieve a value for an option that is not configured on the database column or partition that stores the BLOB.

Syntax

LobOptionValue getOptions(
   LobOptionType optType);
Parameter Description
optType
The LobOptionType setting requested. These may be combined using bitwise or (|) to avoid server round trips. See Table 7-1, "Values of Type LobOptionType" and Table 7-2, "Values of Type LobOptionValue"


getStream()

Returns a Stream object from the BLOB. If a stream is already open, it is disallowed to open another stream on Blob object, so the user must always close the stream before performing any Blob object operations.

Syntax

Stream* getStream(
   unsigned int offset = 1,
   unsigned int amount = 0);
Parameter Description
offset
The starting position at which to begin reading data from the BLOB. If offset is not specified, the data is written from the beginning of the BLOB. Valid values are numbers greater than or equal to 1.
amount
The total number of bytes to be read from the BLOB; if amount is 0, the data will be read in a streamed mode from input offset until the end of the BLOB.


isInitialized()

Tests whether the Blob object is initialized. If the Blob object is initialized, then TRUE is returned; otherwise, FALSE is returned.

Syntax

bool isInitialized() const;

isNull()

Tests whether the Blob object is atomically NULL. If the Blob object is atomically NULL, then TRUE is returned; otherwise, FALSE is returned.

Syntax

bool isNull() const;

isOpen()

Tests whether the BLOB is open. If the BLOB is open, then TRUE is returned; otherwise, FALSE is returned.

Syntax

bool isOpen() const;

length()

Returns the number of bytes in the BLOB.

Syntax

unsigned int length() const;

open()

Opens the BLOB in read/write or read-only mode.

Syntax

void open(
   LobOpenMode mode = OCCI_LOB_READWRITE);
Parameter Description
mode
The mode the BLOB is to be opened in. Valid values are:
  • OCCI_LOB_READWRITE

  • OCCI_LOB_READONLY



operator=()

Assigns a BLOB to the current BLOB. The source BLOB gets copied to the destination BLOB only when the destination BLOB gets stored in the table.

Syntax

Blob& operator=(
   const Blob &srcBlob);
Parameter Description
srcBlob
The source BLOB from which to copy data.


operator==()

Compares two Blob objects for equality. Two Blob objects are equal if they both refer to the same BLOB. Two NULL Blob objects are not considered equal. If the Blob objects are equal, then TRUE is returned; otherwise, FALSE is returned.

Syntax

bool operator==(
   const Blob &srcBlob) const;
Parameter Description
srcBlob
The source BLOB to be compared with the current BLOB.


operator!= ()

Compares two Blob objects for inequality. Two Blob objects are equal if they both refer to the same BLOB. Two NULL Blob objects are not considered equal. If the Blob objects are not equal, then TRUE is returned; otherwise, FALSE is returned.

Syntax

bool operator!=(
   const Blob &srcBlob) const;
Parameter Description
srcBlob
The source BLOB to be compared with the current BLOB.


read()

Reads a part or all of the BLOB into a buffer. The actual number of bytes read is returned.

Syntax

unsigned int read(
   unsigned int amt,
   unsigned char *buffer,
   unsigned int bufsize,
   unsigned int offset = 1) const;
Parameter Description
amt
The number of bytes to be read. Valid values are numbers greater than or equal to 1.
buffer
The buffer that the BLOB data is to be read into. Valid values are numbers greater than or equal to amt.
buffsize
The size of the buffer that the BLOB data is to be read into. Valid values are numbers greater than or equal to amt.
offset
The starting position at which to begin reading data from the BLOB. If offset is not specified, the data is written from the beginning of the BLOB.


setEmpty()

Sets the Blob object to empty.

Syntax Description
void setEmpty();
Sets the Blob object to empty.
void setEmpty(
   const Connection* connectionp);
Sets the Blob object to empty and initializes the connection pointer to the passed parameter.

Parameter Description
connectionp
The new connection pointer for the BLOB object.


setNull()

Sets the Blob object to atomically NULL.

Syntax

void setNull();

setOptions()

Specifies a LobOptionValue for a particular LobOptionType. Enables advanced compression, encryption and deduplication of BLOBs. See Table 7-1, "Values of Type LobOptionType" and Table 7-2, "Values of Type LobOptionValue".

Will throw an exception if attempting to set or un-set an option that is not configured on the database column or partition that stores the BLOB. Will throw an exception if attempting to turn off encryption in an encrypted BLOB column.

Syntax

void setOptions(
   LobOptionType optType,
   LobOptionValue optValue);
Parameter Description
optType
The LobOptionType setting being specified. These may be combined using bitwise or (|) to avoid server round trips.
optValue
The LobOptionValue setting for the LobOptionType specified by the optType parameter


trim()

Truncates the BLOB to the new length specified.

Syntax

void trim(
   unsigned int newlen);
Parameter Description
newlen
The new length of the BLOB. Valid values are numbers less than or equal to the current length of the BLOB.


write()

Writes data from a buffer into a BLOB. This method implicitly opens the BLOB, copies the buffer into the BLOB, and implicitly closes the BLOB. If the BLOB is already open, use writeChunk() instead. The actual number of bytes written is returned.

Syntax

unsigned int write(
   unsigned int amt,
   unsigned char *buffer,
   unsigned int bufsize,
   unsigned int offset = 1);
Parameter Description
amt
The number of bytes to be written to the BLOB.
buffer
The buffer containing the data to be written to the BLOB.
buffsize
The size of the buffer containing the data to be written to the BLOB. Valid values are numbers greater than or equal to amt.
offset
The starting position at which to begin writing data into the BLOB. If offset is not specified, the data is written from the beginning of the BLOB. Valid values are numbers greater than or equal to 1.


writeChunk()

Writes data from a buffer into a previously opened BLOB. The actual number of bytes written is returned.

Syntax

unsigned int writeChunk(
   unsigned int amount,
   unsigned char *buffer,
   unsigned int bufsize,
   unsigned int offset = 1);
Parameter Description
amt
The number of bytes to be written to the BLOB.
buffer
The buffer containing the data to be written to the BLOB.
buffsize
The size of the buffer containing the data to be written to the BLOB. Valid values are numbers greater than or equal to amt.
offset
The starting position at which to begin writing data into the BLOB. If offset is not specified, the data is written from the beginning of the BLOB. Valid values are numbers greater than or equal to 1.