4D Doc Center : REAL TO BLOB

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4D v14.3

BLOB

REAL TO BLOB


REAL TO BLOB ( real ; blob ; realFormat {; offset \| *} )

Parameter	Type	Description
real	Real	Real value to write into the BLOB
blob	BLOB	BLOB to receive the Real value
realFormat	Longint	0 Native real format 1 Extended real format 2 Macintosh Double real format 3 Windows Double real format
offset \| *	Variable, Operator	Offset within the BLOB (expressed in bytes) or * to append the value
		New offset after writing if not *

Description

The REAL TO BLOB command writes the Real value real into the BLOB blob.

The realFormat parameter fixes the internal format and byte ordering of the Real value to be written. You pass one of the following predefined constants provided by 4D:

Constant	Type	Value
Extended real format	Longint	1
Macintosh double real format	Longint	2
Native real format	Longint	0
PC double real format	Longint	3

Platform Independence Note: If you exchange BLOBs between Macintosh and PC platforms, it is up to you to manage real formats and byte swapping issues when using this command.

If you specify the * optional parameter, the Real value is appended to the BLOB; the size of the BLOB is extended accordingly. Using the * optional parameter, you can sequentially store any number of Integer, Long Integer, Real or Text values (see other BLOB commands) in a BLOB, as long as the BLOB fits into memory.

If you do not specify the * optional parameter or the offset variable parameter, the Real value is stored at the beginning of the BLOB, overriding its previous contents; the size of the BLOB is adjusted accordingly.

If you pass the offset variable parameter, the Real value is written at the offset (starting from zero) within the BLOB. No matter where you write the Real value, the size of the BLOB is increased according to the location you passed (plus up to 8 or 10 bytes, if necessary). New allocated bytes, other than the ones you are writing, are initialized to zero.

After the call, the offset variable parameter is returned, incremented by the number of bytes that have been written. Therefore, you can reuse that same variable with another BLOB writing command to write another value.

Example 1

After executing this code:

 C_REAL(vrValue)

 vrValue:=...

 REAL TO BLOB(vrValue;vxBlob;Native real format)

On all platforms, the size of vxBlob is 8 bytes

Example 2

After executing this code:

 C_REAL(vrValue)

 vrValue:=...

 REAL TO BLOB(vrValue;vxBlob;Extended real format)

On all platforms, the size of vxBlob is 10 bytes

Example 3

After executing this code:

 C_REAL(vrValue)

 vrValue:=...

 REAL TO BLOB(vrValue;vxBlob;Macintosh double real format) ` or Windows double real format

On all platforms, the size of vxBlob is 8 bytes

Example 4

After executing this code:

 SET BLOB SIZE(vxBlob;100)

 C_REAL(vrValue)

 vrValue:=...

 INTEGER TO BLOB(vrValue;vxBlob;PC double real format) ` or Macintosh double real format

On all platforms, the size of vxBlob is 8 bytes

Example 5

After executing this code:

 SET BLOB SIZE(vxBlob;100)

 REAL TO BLOB(vrValue;vxBlob;Extended real format;*)

On all platforms, the size of vxBlob is 110 bytes
On all platforms, the real value is stored at the bytes #100 to #109
The other bytes of the BLOB are left unchanged

Example 6

After executing this code:

 SET BLOB SIZE(vxBlob;100)

 C_REAL(vrValue)

 vrValue:=...

 vlOffset:=50

 REAL TO BLOB(vrValue;vxBlob;PC double real format;vlOffset) ` or Macintosh double real format

On all platforms, the size of vxBlob is 100 bytes
On all platforms, the real value is stored in the bytes #50 to #57
The other bytes of the BLOB are left unchanged
The variable vlOffset has been incremented by 8 (and is now equal to 58)