Is there a 1 Megabyte limit on memo fields using the OleDB provider?
I received a question:
My customer is under the impression that there is a size limit (of about 1 meg) on what can be retrieved from a FoxPro Memo field using the OleDb provider? Can someone confirm or refute this???
So I wrote some code that creates a table with a memo field, adds a record, with a 16 Meg string (See Visual FoxPro System Capacities)
There are many layers of software being used here that might limit the string length:
- The VFP String variable limit
- The VFP memo size limit
- ADO recordset string limit
- COM string limit
Looking at the Visual FoxPro System Capacities, I see something I wrote years ago!
64 bits = 8 bytes
Largest number = 10 ^ 308 = 2 ^ 1023
-> 10 bits per exponent + 1 for exponent sign plus 1 for number sign => 12 bits
Leaving 52 bits for the mantissa + 1 for implied normalized bit -> 53 bits
LOG10(2^53) = 15.95 decimal digits accuracy
lcCurDir = JustPath(Sys(16))
cd (lcCurDir)
CLOSE DATABASES ALL
ERASE testtab1.*
CREATE TABLE testtab1 (name c(10),data m)
INSERT INTO testtab1 VALUES ("test",REPLICATE("A",1.6e7))
?LEN(data),LOG10(LEN(data))
CLOSE DATABASES ALL
LOCAL loRs as adodb.recordset
loConn = CREATEOBJECT('ADODB.Connection')
lcPath = (lcCurDir)
loConn.ConnectionString = "Provider=VFPOLEDB.1;Data Source="+lcPath +";Mode=ReadWrite;Password='';Collating Sequence=MACHINE"
loConn.Open
? loConn.Properties('Provider version').value
loRs=loConn.Execute("select * from testtab1")
?lors.Fields(0).Value
?LEN(lors.Fields(1).Value)
loConn.Close
