pqReadData() -- backend closed the channel unexpectedly.

i have to call one c function users() present in one c file which is as
follows:

#include <stdio.h>
#include "pgsql/postgres.h"
void users();

int main()
{
users();
}

void users()
{
         FILE *fp;
         fp = fopen("/home/suresh/trigger/test.txt","w");
         fputs("Hello this is c function",fp);
}

the funcion that calls users() from c file is as follows:

create FUNCTION users() returns opaque as '/var/lib/pgsql/test.so' language
'C';

the trigger that calls this fuction is as follows:

CREATE TRIGGER users_trg before insert on users for each row execute
procedure users();

now when i am any value in my table it gives the error :

pqReadData() -- backend closed the channel unexpectedly.
         This probably means the backend terminated abnormally
         before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.

i cannot find the solution to this problem.
please help.