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getting started with libpq and postgresql

From
"Damar Thapa"
Date:
Hi!,
 
I am trying to use libpq (C interface) to write client program to access PostGreSQL database. 
 
I copied an example program from PostgreSQL: Introduction  and Concepts by Bruce Momjian.
 
To compile the above said program, I did:
 
    gcc -o ctest ctest.c        /*I named the copied program as ctest.c*/
 
I got an error message, saying "libpq-fe.h not found".
 
In my linux RH7.1, I found libpq-fe.h in /usr/include/pgsql directory, so I replace the line '#include "libpq-fe.h"' in ctest.c with'#include "/usr/include/pgsql/libpq-fe.h"'.   I did not get the above-said error, but the followings:
 
/tmp/ccgwexRo.0: In function 'main':
 
/tmp/ccgwexRr.o(.txt+0x12): undefined reference to 'PQconnectdb'
 /tmp/ccgwexRr.o(.txt+0x2b): undefined reference to 'PQstatus'
/tmp/ccgwexRr.o(.txt+0x5c): undefined reference to 'PQerrorMessage'
/tmp/ccgwexRr.o(.txt+0xd4): undefined reference to 'PQexec'
 
7 more lines like these.
 
Having these errors, I obviously have not done things correctly. 
 
Do I have to do any setting in gcc or compilation has to be done differently.
 
Any help would be highly appreciated.
 
With regards,
 
Damar Thapa
 
 

Re: getting started with libpq and postgresql

From
Antonio Sergio de Mello e Souza
Date:
Damar Thapa wrote:

> In my linux RH7.1, I found libpq-fe.h in /usr/include/pgsql directory, 
> so I replace the line '#include "libpq-fe.h"' in ctest.c 
> with'#include "/usr/include/pgsql/libpq-fe.h"'.   I did not get the 
> above-said error, but the followings:
>
>  
>
> /tmp/ccgwexRo.0: In function 'main':
>
>  
>
> /tmp/ccgwexRr.o(.txt+0x12): undefined reference to 'PQconnectdb'
>
>  /tmp/ccgwexRr.o(.txt+0x2b): undefined reference to 'PQstatus'
> /tmp/ccgwexRr.o(.txt+0x5c): undefined reference to 'PQerrorMessage'
>
> /tmp/ccgwexRr.o(.txt+0xd4): undefined reference to 'PQexec'
>
>  
>
> Do I have to do any setting in gcc or compilation has to be done 
> differently.
>
Hi,

You need to tell the compiler where the include files and libraries are. 
Try this command:

gcc -I /usr/include/pgsql -L /usr/lib/pgsql -lpq -o ctest ctest.c

The -I option says that the include files are located at 
/usr/include/pgsql, the -L says that the library can be found at 
/usr/lib/pgsql and the -lpq option shows that you're using the pq 
library. This is just an example, the actual paths in your system can be 
different.
Also, you need to check  the contents of the /etc/ld.so.conf file. Add a 
line with the path to the library if it isn't already there. Remember to 
run, as root, the command /sbin/ldconfig if you change that file.

Regards,

Antonio Sergio