This example demonstrates INSERT, UPDATE, and SELECT statements
with the DB2 CLOB datatype in stream
mode and std::strings.
#include <iostream>
#include <string>
using namespace std;
#include <stdio.h>
#define OTL_DB2_CLI // Compile OTL 4.0/DB2 CLI
#define OTL_STL // enable OTL support for STL
#if (defined(__clang__) || defined(__GNUC__)) && \
(defined(OTL_CPP_14_ON) || defined(OTL_CPP_17_ON))
#include <experimental/string_view>
#define OTL_STD_STRING_VIEW_CLASS std::experimental::string_view
#elif defined(_MSC_VER) && (_MSC_VER>=1910) && defined(OTL_CPP_17_ON)
// VC++ 2017 or higher when /std=c++latest is used
#include <string_view>
#define OTL_STD_STRING_VIEW_CLASS std::string_view
#endif
#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 CLOB to be written.
// It is required for bakward compatibility
#if defined(OTL_STD_STRING_VIEW_CLASS)
OTL_STD_STRING_VIEW_CLASS f2_sv(f2.c_str(),f2.length());
lob<<f2_sv; // writing first chunk into the lob
#else
lob<<f2; // writing first chunk into the lob
#endif
f2.erase();
f2.append(23122,'*');
f2 += '?';
#if defined(OTL_STD_STRING_VIEW_CLASS)
OTL_STD_STRING_VIEW_CLASS f2_sv(f2.c_str(),f2.length());
lob<<f2_sv; // writing second chunk into the lob
#else
lob<<f2; // writing second chunk into the lob
#endif
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 CLOB to be written
for(int i=1;i<=4;++i)
lob<<f2; // writing chunks of the CLOB 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 CLOBs, 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 CLOB
lob.setStringBuffer(40000); // Set a bigger internal buffer (default is 4096 bytes)
// for reading chunks of the CLOB, 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 CLOB stream by reading the CLOB 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@db2sql"); // 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 clob(1M))"
); // 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;
}
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
Copyright © 1996-2023, Sergei Kuchin, email: skuchin@gmail.com, skuchin@gmail.com .
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. THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.