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Old 02-17-2014, 02:18 AM   #1
Nikhil_Lagwankar
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postgres output from query to file via c code


Hi,


I'm using CentOS 6.4 (Final) and PostgresSQL 8.4.

I have to get the output of a query to a text file.

If i do the manual way this works however I need to accomplish this using the C - code.

My C code is as below

Code:
int     main() {
PGconn          *conn;
PGresult        *res;
int             rec_count;
int             row;
int             col;
char st[50]="\\o /usr/tmp/posttemp/test.txt";
puts(st);


 conn = PQconnectdb("dbname=postgres user=postgres password=postgres");

 if (PQstatus(conn) == CONNECTION_BAD) {
	 puts("We were unable to connect to the database");
	 exit(0);
 }
 

 res = PQexec(conn,st);

 res = PQexec(conn,"select * from pg_catalog.pg_user");

 if (PQresultStatus(res) != PGRES_TUPLES_OK) {
	 puts("We did not get any data!");
	 exit(0);
 }

rec_count = PQntuples(res);

 printf("We received %d records.\n", rec_count);
 puts("==========================");

 for (row=0; row<rec_count; row++) {
	 for (col=0; col<3; col++) {
	         printf("%s\t", PQgetvalue(res, row, col));
	 }
	 puts("");
 }

 puts("==========================");

 PQclear(res);

 PQfinish(conn);

 return 0;
}
There's no error in code compilation.

Query gives o/p on the terminal via this code however none in file specified.

What's going wrong here?
 
Old 02-17-2014, 07:47 AM   #2
michaelk
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The \o is only an option of psql. You need to use standard c to open/write files.

What is the res value when you execute PQexec(conn,st)?

Last edited by michaelk; 02-17-2014 at 07:49 AM.
 
1 members found this post helpful.
Old 02-18-2014, 10:56 PM   #3
Nikhil_Lagwankar
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Quote:
Originally Posted by michaelk View Post
The \o is only an option of psql. You need to use standard c to open/write files.

What is the res value when you execute PQexec(conn,st)?
There's nothing in res....I did a printf of res and it came blank.
 
Old 02-19-2014, 12:52 AM   #4
Nikhil_Lagwankar
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Quote:
Originally Posted by michaelk View Post
The \o is only an option of psql. You need to use standard c to open/write files.
Thanks, This works ...
 
Old 02-19-2014, 05:00 AM   #5
michaelk
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A little but this should work too.
http://www.postgresql.org/docs/9.1/static/sql-copy.html
 
  


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