asked on

C++ Build: read data from BLOB?

A table will form as below after running the C++ Builder code:

1 [BLOB] [*BLOB*] [BLOB] [BLOB] [BLOB] [BLOB] [Blob]
2 [BLOB] [*BLOB*] [BLOB] [BLOB] [BLOB] [BLOB] [Blob]
3 ......

1000[BLOB] [*BLOB*] [BLOB] [BLOB] [BLOB] [BLOB] [Blob]

I need that, after only click the second [BLOB], all data in this column of all raws will be saved in

ascii format. Howevr, only the data in the first BLOB was saved, all other data was NOT saved in the

file. How to modify it?
High points will be given if your modification does work!

//_________________ part of code _________________
void TMainForm::ExportBLOB(AnsiString FileName, AnsiString FieldName)
{
int SaveNo = DBTable->RecNo;
DBTable->First();DBTable->Next();
TFileStream* File=new TFileStream(FileName, fmCreate);
while(!DBTable->Eof){ //***

TField* Field=DBTable->FieldByName(FieldName);
TFieldType FieldType=Field->DataType;
if(FieldType!=ftBlob)
throw Exception("Invalid Call To ExportBlob() - Field Not A BlobType");

TBlobField* ThisBlob;
ThisBlob=(TBlobField*)Field;
TBlobStream* ThisBlobStream;
ThisBlobStream=new TBlobStream(ThisBlob, bmRead);

int PointsToRead=ThisBlobStream->Size/sizeof(short);
if(PointsToRead<=0)
{
delete ThisBlobStream;
return;
}

short* Data=new short[PointsToRead];

ThisBlobStream->Seek(0, soFromBeginning);
ThisBlobStream->Read(Data, ThisBlobStream->Size);

for(int i=0; i<PointsToRead; i++)
{
AnsiString Text;
Text+=Data[i];
Text+="\n";
File->Write(Text.c_str(), Text.Length());
}

delete ThisBlobStream;
delete [] Data;
DBTable->Next();DBTable->Next();DBTable->Next();DBTable->Next();
DBTable->Next();DBTable->Next();
} //***
delete File;
DBTable->RecNo = SaveNo;

}

kretzschmar

guessing you misunderstand the next-method
(this goes to the next record and not to the next field)

therefore
DBTable->First();DBTable->Next();
should be
DBTable->First(); //except you will skip the first record

and

DBTable->Next();DBTable->Next();DBTable->Next();DBTable->Next();
DBTable->Next();DBTable->Next();
should be
DBTable->Next(); //only one is needed to go to the next record

just a guess

meikl ;-)

kretzschmar

also you could use the stream copy-method instead of saving bytewise

Johncili

ASKER

Thanks,

However, how to write out those marked BLOB (every raw, second column, e.g., every record, 2nd field only)?

Looking for your advise.

Johncili

ASKER

How to write out data in every 2nd field?

Johncili

ASKER

If I know that the name of 2nd field is "BLOB2", how to write out only this field of every record?

kretzschmar

well,

i can show only how i would do it in delphi
(because i'm no c-coder)

i guess your table contains 7 blob-fields
so i would code something like this

procedure blobexport(ATable : TTable; AFieldNo : Integer; AFilename : String);
var
fs : tfilestream;
begin
if not ATable.Active then //be sure the table is open
ATable.Open;
fs := tfilestream.create(AFileName, fmCreate); //new file
ATable.First; //from beginning
if ATable.Fields[AFieldNo-1].IsBlob Then //is it a blobfield
begin
while not ATable.Eof do //to end
begin
If Not TBlobField(ATable.Fields[AFieldNo-1]).IsEmpty Then //only for not empty contents
begin
TBlobField(ATable.Fields[AFieldNo-1]).SaveToStream(fs); //write to the stream, with a typeconversion
fs.write(#13#10,2); //new line
end;
end;
end;
fs.free; //close file
end;

well, just from head, there may typos

meikl ;-)

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kretzschmar

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kretzschmar

any success?
any problems?

kretzschmar

john, did you get it work?