OTL 4.0, Example 382 (Insert/Update/Select, MySQL LONGTEXT in stream mode, and std:strings)

This example demonstrates INSERT, UPDATE, and SELECT statements with the MySQL LONGTEXT datatype in stream mode and std::strings.

Source Code

#include <iostream>
#include <string>
using namespace std;

#include <stdio.h>

#define OTL_ODBC // Compile OTL 4.0/ODBC
#define OTL_STL // enable OTL support for STL
#include <otlv4.h> // include the OTL 4.0 header file

otl_connect db; // connect object

void insert()
// insert rows into table
{
 string f2; 
 otl_stream o; // defined an otl_stream variable
 o.set_lob_stream_mode(true); // set the "lob stream mode" flag
 o.open(1, // buffer size has to be set to 1 for operations with LOBs
        "insert into test_tab values(:f1<int>,:f2<varchar_long>) ",
            // SQL statement
        db // connect object
       );
 o.set_commit(0); // setting stream "auto-commit" to "off". It is required
                  // when LOB stream mode is used.

 otl_lob_stream lob; // LOB stream for reading/writing unlimited number
                     // of bytes regardless of the buffer size.
 for(int i=1;i<=20;++i){
  f2.erase();
  f2.append(50000,'*');
  f2 += '?';
  o<<i;
  o<<lob; // Initialize otl_lob_stream by writing it
          // into otl_stream

  lob.set_len(50001+23123); // setting the total size of
                            // the LONGTEXT to be written.
   // It is required for bakward compatibility
 
  lob<<f2; // writing first chunk of the LONGTEXT into lob

  f2.erase();
  f2.append(23122,'*');
  f2 += '?';
  lob<<f2; // writing the second chunk of the LONGTEXT into lob
  lob.close(); // closing the otl_lob_stream
 }

 db.commit(); // committing transaction.
}

void update()
// insert rows in table
{ 
 string f2; 
 otl_stream o; // defined an otl_stream variable
 o.set_lob_stream_mode(true); // set the "lob stream mode" flag
 o.open(1, // buffer size has to be set to 1 for operations with LOBs
        "update test_tab "
        "   set f2=:f2<varchar_long> "
        "where f1=:f1<int> ",
            // SQL statement
        db // connect object
       );
 otl_lob_stream lob;
 o.set_commit(0); // setting stream "auto-commit" to "off". 
 f2.append(6000,'#');
 f2+='?';
 o<<lob; // Initialize otl_lob_stream by writing it
         // into otl_stream.
 o<<5;
 lob.set_len(6001*4); // setting the total size of of the LONGTEXT to be written
 for(int i=1;i<=4;++i)
  lob<<f2; // writing chunks of the LONGTEXT into the otl_lob_stream
 lob.close(); // closing the otl_lob_stream
 db.commit(); // committing transaction

}

void select()
{ 
 string f2;
 otl_stream i; // defined an otl_stream variable
 i.set_lob_stream_mode(true); // set the "lob stream mode" flag
 i.open(1, // buffer size. To read LONGTEXTs, it should be set to 1
        "select * from test_tab where f1>=:f11<int> and f1<=:f12<int>*2",
          // SELECT statement
        db // connect object
       ); 
   // create select stream
 
 int f1;
 otl_lob_stream lob; // Stream for reading LONGTEXT

 lob.setStringBuffer(40000); // Set a bigger internal buffer (default is 4096 bytes)
                             // for reading chunks of the LONGTEXT, before each chunk
                             // gets appended to the output string.
 i<<4<<4; // assigning :f11 = 4, :f12 = 4
   // SELECT automatically executes when all input variables are
   // assigned. First portion of output rows is fetched to the buffer

 while(!i.eof()){ // while not end-of-data
  i>>f1;
  cout<<"f1="<<f1;
  i>>lob; // initializing LONGTEXT stream by reading the LONGTEXT reference 
          // into the otl_lob_stream from the otl_stream.
  lob>>f2;
  cout<<", f2="<<f2[0]<<f2[f2.length()-1]<<", len="<<(int)f2.length()<<endl;
  lob.close(); // closing the otl_lob_stream. This step may be skipped.
  
 }

}

int main()
{
 otl_connect::otl_initialize(); // initialize the database API environment
 try{

  db.rlogon("scott/tiger@mysql35"); // connect to the database

  otl_cursor::direct_exec
   (
    db,
    "drop table test_tab",
    otl_exception::disabled // disable OTL exceptions
   ); // drop table

  otl_cursor::direct_exec
   (
    db,
    "create table test_tab(f1 int, f2 longtext)"
    );  // create table

  insert(); // insert records into table
  update(); // update records in table
  select(); // select records from table

 }

 catch(otl_exception& p){ // intercept OTL exceptions
  cerr<<p.msg<<endl; // print out error message
  cerr<<p.stm_text<<endl; // print out SQL that caused the error
  cerr<<p.var_info<<endl; // print out the variable that caused the error
 }

 db.logoff(); // disconnect from the database

 return 0;

}

Output

f1=4, f2=*?, len=73124
f1=5, f2=#?, len=24004
f1=6, f2=*?, len=73124
f1=7, f2=*?, len=73124
f1=8, f2=*?, len=73124

Examples Contents Go Home

Permission to use, copy, modify and redistribute this document for any purpose is hereby granted without fee, provided that the above copyright notice appear in all copies.