Getting clob

Question

A Run-Time error is raised by Visual Studio 2005Prof in my code when reading column of type clob and assigning its value to a std::string.
This is the code:
     void GetClob( unsigned int col, std::string & clobStr )
          if( resultSet_->isNull( col ) )
               return;
          oracle::occi::Clob clob = resultSet_->getClob( col );
          if( clob.isNull() )
               return;
          clob.open( oracle::occi::OCCI_LOB_READONLY );
          unsigned int clobSize = clob.length();
          assert( clobSize > 0 );
          clobStr.resize( clobSize );
          clob.read( clobSize, (unsigned char *)&clobStr[ 0 ], clobSize );
          clob.close();
The VS error occurs when leaving the scope of GetClob method and the message says:
Run-Time Check Failure #2 - Stack around the variable 'clob' was corrupted. I can see that clobStr variable contains the actual correct string.
======================
Even if I reduce the code like this:
     void GetClob( unsigned int col, std::string & clobStr )
          if( resultSet_->isNull( col ) )
               return;
          oracle::occi::Clob clob = resultSet_->getClob( col );
          if( clob.isNull() )
               return;
clob.open( oracle::occi::OCCI_LOB_READONLY );
//          unsigned int clobSize = clob.length();
//          assert( clobSize > 0 );
//          clobStr.resize( clobSize );
//          clob.read( clobSize, (unsigned char *)&clobStr[ 0 ], clobSize );
          clob.close();
I still get the same error.
Please can you 1) comment on the above code, and/or 2) provide a sample code how reading columns of clob type should be handled?
I can read numeric columns w/o any problems.
I am using WinXP, occi 10.2.0.3.0 with the latest Patch 10 downloaded from here http://www.oracle.com/technology/tech/oci/occi/occidownloads.html.
Thank you for your help! This problem has taken me a lot of time already.

Answer 1

Try the following code sample.
#include <iostream>
#include <fstream>
#include <occi.h>
using namespace oracle::occi;
using namespace std;
* The demo sample has starts from startDemo method. This method is called
* by main. startDemo calls other methods, the supporting methods for
* startDemo are,
* insertRows - insert the rows into the table
* dataRollBack - deletes the inserted rows
* populateClob - populates a given clob
* dumpClob - prints the clob as an integer stream
// These will tell the type of read/write we use
#define USE_NORM 1
#define USE_CHUN 2
#define USE_BUFF 3
/* Buffer Size */
#define BUFSIZE 200;
class occiClob
public:
string username;
string password;
string url;
void insertRows (Connection *conn)
throw (SQLException)
Statement *stmt = conn->createStatement ("INSERT INTO electronic_media(product_id,ad_id,ad_composite,ad_sourcetext) VALUES (:v1,:v2,:v3,:v4)");
Blob blob(conn);
blob.setEmpty();
Clob clob(conn);
clob.setEmpty();
stmt->setInt(1,6666);
stmt->setInt(2,11001);
stmt->setBlob(3,blob);
stmt->setClob(4,clob);
stmt->executeUpdate();
stmt->setSQL ("INSERT INTO electronic_media(product_id,ad_id,ad_composite,ad_sourcetext) VALUES (:v1, :v2, :v3, :v4)");
stmt->setInt(1,7777);
stmt->setInt(2,11001);
stmt->setBlob(3,blob);
stmt->setClob(4,clob);
stmt->executeUpdate();
stmt->setSQL ("INSERT INTO electronic_media(product_id,ad_id,ad_composite,ad_sourcetext) VALUES (:v1, :v2, :v3, :v4)");
stmt->setInt(1,8888);
stmt->setInt(2,11001);
stmt->setBlob(3,blob);
stmt->setClob(4,clob);
stmt->executeUpdate();
conn->commit();
conn->terminateStatement (stmt);
void dataRollBack (Connection *conn)
throw (SQLException)
Statement *stmt = conn->createStatement ("DELETE FROM electronic_media WHERE product_id=6666 AND ad_id=11001");
stmt->executeUpdate();
stmt->setSQL("DELETE FROM electronic_media WHERE product_id=7777 AND ad_id=11001");
stmt->executeUpdate();
stmt->setSQL("DELETE FROM electronic_media WHERE product_id=8888 AND ad_id=11001");
stmt->executeUpdate();
conn->commit();
conn->terminateStatement (stmt);
* populating the clob uses write method;
void populateClob (Clob &clob,unsigned int way)
throw (SQLException)
unsigned int bufsize=BUFSIZE;
if (way == USE_NORM)
cout << "Populating the Clob using write method" << endl;
unsigned int offset=1;
unsigned char *buffer = new unsigned char[bufsize];
strcpy((char *)buffer,
"Just for source text content(added using write method)");
unsigned int size=strlen((char *)buffer);
unsigned int bytesWritten=clob.write (size,buffer, size,offset);
//cout <<"Bytes Written : " << bytesWritten << endl;
delete[] buffer;
else if(way==USE_CHUN)
cout << "Populating the Clob using writeChunk method" << endl;
unsigned int offset=1;
unsigned int pieceCount = 4;
unsigned char *buffer = new unsigned char[bufsize*pieceCount];
strcpy((char *)buffer,
"Just for source text content(added using writeChunk method)");
unsigned int size=strlen((char *)buffer);
// Open the clob for writeChunk
clob.open(OCCI_LOB_READWRITE);
for (int i = 0; i < pieceCount; ++i,offset+=size)
clob.writeChunk(size,buffer,size,offset);
cout << "Clob Size " << clob.length() << endl;
delete[] buffer;
clob.close();
else if(way==USE_BUFF)
// Uses stream here
cout << "Populating the Clob using writeBuffer(Stream) method" << endl;
char file = (char )"clobdemo.dat";
char *buffer = new char[bufsize + 1];
ifstream inFile;
inFile.open(file,ios::in);
if (!inFile)
cout << "clobdemo.dat file not found\n";
delete[] buffer;
return;
unsigned int size;
Stream *strm=clob.getStream();
while(inFile)
memset (buffer, NULL, bufsize + 1);
inFile.read(buffer,bufsize);
strm->writeBuffer(buffer,strlen(buffer));
strcpy(buffer,"This piece for writeLastBuffer");
size=strlen(buffer);
strm->writeLastBuffer(buffer,size);
clob.closeStream(strm);
inFile.close();
delete[] buffer;
cout << "Populating the Clob - Success" << endl;
* printing the clob data as integer stream
void dumpClob (Clob &clob,unsigned int way)
throw (SQLException)
unsigned int size=BUFSIZE;
unsigned int offset = 1;
if (clob.isNull())
cout << "Clob is Null\n";
return;
unsigned int cloblen = clob.length();
cout << "Length of Clob : "<< cloblen << endl;
if (cloblen == 0)
return;
unsigned char *buffer= new unsigned char[size];
memset (buffer, NULL, size);
if (way==USE_NORM)
cout << "Dumping clob (using read ): ";
int bytesRead=clob.read(size,buffer,size,offset);
for (int i = 0; i < bytesRead; ++i)
cout << buffer;
cout << endl;
else if(way==USE_BUFF)
Stream *inStream = clob.getStream (1,0);
cout << "Dumping clob(using stream): ";
int bytesRead=(inStream->readBuffer((char *)buffer, size));
while (bytesRead > 0)
for (int i = 0; i < bytesRead; ++i)
cout << buffer[i];
bytesRead=(inStream->readBuffer((char *)buffer, size));
cout << endl;
clob.closeStream (inStream);
delete []buffer;
occiClob ()
* default values of username & password
username = "HR";
password = "HR";
url = "";
void setUsername (string u)
username = u;
void setPassword (string p)
password = p;
void setUrl (string u)
url = u;
void runSample ()
throw (SQLException)
Environment *env = Environment::createEnvironment (
Environment::DEFAULT);
Connection *conn = env->createConnection (username, password, url);
insertRows (conn);
// Selecting and modifying the clob column of the table
string sqlQuery =
"SELECT product_id,ad_id,ad_sourcetext FROM electronic_media FOR UPDATE";
Statement *stmt1 = conn->createStatement (sqlQuery);
ResultSet *rset1 = stmt1->executeQuery ();
cout << "Query :" << sqlQuery << endl;
unsigned int way=USE_NORM;
while (rset1->next ())
cout << "Product_id : " << (int)rset1->getInt(1) << endl;
cout << "Ad_id : " << (int)rset1->getInt(2) << endl;
Clob clob = rset1->getClob (3);
dumpClob (clob, USE_NORM);
if (way==USE_NORM)
populateClob(clob,USE_NORM);
way=USE_CHUN;
else if(way==USE_CHUN)
populateClob(clob,USE_CHUN);
way=USE_BUFF;
else if(way==USE_BUFF)
populateClob(clob,USE_BUFF);
way=USE_NORM;
stmt1->executeUpdate();
stmt1->closeResultSet (rset1);
// Printing after updating the clob content.
way = USE_BUFF;
sqlQuery = "SELECT product_id, ad_id, ad_sourcetext FROM electronic_media \
ORDER BY product_id";
Statement *stmt2 = conn->createStatement (sqlQuery);
ResultSet *rset2 = stmt2->executeQuery ();
cout << "Query :" << sqlQuery << endl;
while (rset2->next ())
cout << "Product_id : " << (int)rset2->getInt(1) << endl;
cout << "Ad_id : " << (int)rset2->getInt(2) << endl;
Clob clob = rset2->getClob (3);
if (way==USE_NORM)
dumpClob (clob, USE_NORM);
way=USE_BUFF;
else if(way==USE_BUFF)
dumpClob (clob, USE_BUFF);
way=USE_NORM;
stmt2->closeResultSet (rset2);
dataRollBack(conn);
conn->terminateStatement (stmt1);
conn->terminateStatement (stmt2);
env->terminateConnection (conn);
Environment::terminateEnvironment (env);
};//end of class occiClob
int main (void)
try
occiClob *b = new occiClob ();
b->setUsername ("HR");
b->setPassword ("HR");
b->runSample ();
catch (exception &e)
cout << e.what();