Thread: Difficulty getting started with Postgres C++ interface

Hi there,

I have been successfully using the perl DBI interface for some time and
have just begun a new project which needs to be written in C++. My
problem is that I am unable to compile even a simple C++ program without
error.

I am running a Mandrake 8.1 distribution of Linux, Postgres version 7.1.2
(with the libpq++ stuff that came with it) and trying to compile with
g++.

my program is:

#include <iostream.h>
#include "libpq++.h"

int main()
{// Open the connection to the database and make sure it is OKconst char* dbName="dbname=dwright";PgDatabase
data("dbName");
/*    if ( data.ConnectionBad() ) {    cout << "Connection was unsuccessful..." << endl;    cout << "Error message
returned:" << data.ErrorMessage() << endl;return 1;}else    cout << "Connection successful... Enter queries below:" <<
endl;
// Interactively obtain and execute queriesExecStatusType status;string buf;int done = 0;while (!done){    cout << ">
";   cout.flush();    getline(cin, buf);    if ( buf != "" )        if ( (status = data.Exec( buf.c_str() ))
   == PGRES_TUPLES_OK )            data.DisplayTuples();        else            cout << "No tuples returned..." << endl
              << "status = " << status << endl                << "Error returned: "                <<
data.ErrorMessage()<< endl;    else        done = 1;} */return 0;
 
} // End main()

Note that I have commented out everything except the connect!!

my command line is:

g++ -I/usr/include/pgsql myc.cpp -o myc

and the error messages are:

/home/dwright/tmp/ccx7SvXE.o: In function `PgDatabase::PgDatabase(char const *)':
/home/dwright/tmp/ccx7SvXE.o(.PgDatabase::gnu.linkonce.t.(char const *)+0x13): undefined reference to
`PgConnection::PgConnection(charconst *)'
 
/home/dwright/tmp/ccx7SvXE.o: In function `PgDatabase::~PgDatabase(void)':
/home/dwright/tmp/ccx7SvXE.o(.gnu.linkonce.t._._10PgDatabase+0x1d): undefined reference to
`PgConnection::~PgConnection(void)'
/home/dwright/tmp/ccx7SvXE.o: In function `PgDatabase type_info function':
/home/dwright/tmp/ccx7SvXE.o(.gnu.linkonce.t.__tf10PgDatabase+0x10): undefined reference to `PgConnection type_info
function'
/home/dwright/tmp/ccx7SvXE.o(.gnu.linkonce.t.__tf10PgDatabase+0x18): undefined reference to `PgConnection type_info
node'
collect2: ld returned 1 exit status

Any assistance will be greatly appreciated.

Regards,
David
-- 
David Wright
912 - 614 Lake Street
St. Catharines, ON  L2N 6P6
Web Site: <http://www.mergetel.com/~dwright>

On Mon, Jan 27, 2003 at 05:42:11PM -0500, David Wright wrote:
> 
> g++ -I/usr/include/pgsql myc.cpp -o myc
> 
> /home/dwright/tmp/ccx7SvXE.o(.PgDatabase::gnu.linkonce.t.(char const *)+0x13): undefined reference to
`PgConnection::PgConnection(charconst *)'
 

If you're going to use a library, you'll have to link to it to get
a working program:

g++ -I/usr/include/pgsql myc.cpp -lpq++ -o myc

You may also have to link to the underlying C library, libpq:

g++ -I/usr/include/pgsql myc.cpp -lpq++ -lpq -o myc



And finally--shameless plug coming up--you may want to use libpqxx
instead of libpq++:
 http://gborg.postgresql.org/project/libpqxx/


Jeroen