connection problem

I have a postgresql installed on a remote machine. I want to connect to it
with libpq but the connection is not successful.
I have this piece of code for connection in my c file:

PGconn *conn=NULL;
char *conn_str="hostaddr=172.16.11.2 port=5432 dbname=postgres
user=postgres password=654321 reqiressl=0";
conn=PGconnectStart(conn_str);
if(PGstatus(conn)=CONNECTION_BAD){

PGerrorMessage(conn);
}
else{

printf("connected");

}

But I can not connect. It exits from the program. I tried also PGconnectdb
but it also did not connect to the databse. But I can connect to it thorough
pgAdmin with the same credentials. Can you help me please urgently!'!!!