reading a blob from a postggreSQL db

Hi,
I would like to read a blob from a PostgreSQL database, osing ODBS and C++.
I have succeded to connect to the database, but i have no idea how to read a certain blob.

If some one could help me with the readBlob() function, I would be pleased
(for example just to read a string of 5 characters that allways are in the beginning of the blob)

Main function:
...
strcpy((char*)SQLStmt,"SELECT groupdata From submap where name = '1860'");

//Prepare And Execute The SQL Statement
//
rc = SQLExecDirect(dbConnection.StmtHandle, SQLStmt, SQL_NTS);

//Read The Results Of The SQL Query
//
if (rc == SQL_SUCCESS)
{
        dbConnection.readBlob();
}

SQLRETURN CODBC_Class::readBlob()
{
    // I need help here.................
        rc = SQLBindCol(StmtHandle, ..............................);
        rc = SQLFetch(StmtHandle);

        //Return The ODBC API Return Code To The Calling Function
        //
        return(rc);
}

Kind regards,
Paul