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Thread: list of databases in C ? libpq ?

list of databases in C ? libpq ?

From
Joao Ferreira gmail
Date:
Hello all,

I need to write an application in C to read the list of databases
currently in the server. very much like a "psql -l"...

but I need it in C ! I never used C before to access PG.

the libpq API seems a bit scary ! Is there anything, shipped with
postgresql, other than libpq that would make my life simpler ?

thanks a lot

Joao

Re: list of databases in C ? libpq ?

From
Alex Hunsaker
Date:
On Fri, May 7, 2010 at 11:18, Joao Ferreira gmail
<joao.miguel.c.ferreira@gmail.com> wrote:
> Hello all,
>
> I need to write an application in C to read the list of databases
> currently in the server. very much like a "psql -l"...

select datname as database from pg_database;

> but I need it in C ! I never used C before to access PG.
>
> the libpq API seems a bit scary ! Is there anything, shipped with
> postgresql, other than libpq that would make my life simpler ?

Maybe ecpg http://www.postgresql.org/docs/current/static/ecpg.html ? I
also hear good things about libpqtypes making some things easier
http://pgfoundry.org/projects/libpqtypes/.

Re: list of databases in C ? libpq ?

From
Steve Atkins
Date:
On May 7, 2010, at 10:18 AM, Joao Ferreira gmail wrote:

> Hello all,
>
> I need to write an application in C to read the list of databases
> currently in the server. very much like a "psql -l"...
>
> but I need it in C ! I never used C before to access PG.
>
> the libpq API seems a bit scary !

It's easier than it looks, really:

PGconn *db;
PGresult *result;
int i;

db = PQconnectdb("host=127.0.0.1 dbname=template1 user=joao password=foo");
if(0 == db || PQstatus(db) != CONNECTION_OK) {
  fprintf(stderr, "Failed to connect to db: %s", db ? PQerrorMessage(db) : "unknown error\n");
  exit(1);
}
result = PQexec(db, "select datname from pg_catalog.pg_database");
if(0 == result || PQresultStatus(result) != PGRES_TUPLES_OK) {
  fprintf(stderr, "Failed to run query: %s", result ? PQresultErrorMessage(result) : "unknown error\n");
  exit(1);
}
for(i=0; i < PQntuples(result); ++i) {
  printf("%s\n", PQgetvalue(result, i, 0));
}
PQclear(result);
PQfinish(db);

(Untested)

> Is there anything, shipped with
> postgresql, other than libpq that would make my life simpler ?

Not for C, I don't think. Other languages (C++, perl ...) have bindings that simplify some things.

Cheers,
  Steve

Re: list of databases in C ? libpq ?

From
Reid Thompson
Date:
On 5/7/2010 1:48 PM, Alex Hunsaker wrote:
> On Fri, May 7, 2010 at 11:18, Joao Ferreira gmail
> <joao.miguel.c.ferreira@gmail.com>  wrote:
>> Hello all,
>>
>> I need to write an application in C to read the list of databases
>> currently in the server. very much like a "psql -l"...
>
The first example in the online docs does exactly that...
http://www.postgresql.org/docs/8.1/static/libpq-example.html

$ cc -I /usr/include/postgresql-8.4/ -lpq libpq.c -o libpqex

$ ./libpqex dbname=test
datname        datdba         encoding       datcollate     datctype       datistemplate  datallowconn
datconnlimit   datlastsysoid  datfrozenxid   dattablespace  datconfig      datacl

template1      10             6              en_US.UTF-8    en_US.UTF-8    t              t              -1
           11563          648            1663                          {=c/postgres,postgres=CTc/postgres}
template0      10             6              en_US.UTF-8    en_US.UTF-8    t              f              -1
           11563          648            1663                          {=c/postgres,postgres=CTc/postgres}
postgres       10             6              en_US.UTF-8    en_US.UTF-8    f              t              -1
           11563          648            1663
test           16384          6              en_US.UTF-8    en_US.UTF-8    f              t              -1
           11563          648            1663
sigcap         16438          0              en_US.UTF-8    en_US.UTF-8    f              t              -1
           11563          648            1663