connecting to questDB with libpqxx - postgresql

Question

Im having an issue connecting to QuestDB with libpqxx, i can establish a connection using the postgresql client as per the instructions here:
https://questdb.io/docs/guidePSQL
however, when i go to connect to QuestDB, using my simple program, that is more-or-less a slightly modified version of the standard "get me started" program:
https://github.com/jtv/libpqxx
#include <iostream>
#include <pqxx/pqxx>
int main(){
try
{
pqxx::connection C(
"user=admin "
"hostaddr=127.0.0.1 "
"password=quest "
"dbname=qdb"
"port=8812 ");
std::cout << "Connected to " << C.dbname() << std::endl;
pqxx::work W{C};
pqxx::result R{W.exec("SELECT name FROM employee")};
std::cout << "Found " << R.size() << "employees:\n";
for (auto row: R)
std::cout << row[0].c_str() << '\n';
std::cout << "Doubling all employees' salaries...\n";
W.exec0("UPDATE employee SET salary = salary*2");
std::cout << "Making changes definite: ";
W.commit();
std::cout << "OK.\n";
}
catch (std::exception const &e)
{
std::cerr << e.what() << '\n';
return 1;
}
return 0;
}
.. i get an error:
could not connect to server: Connection refused
Is the server running on host "127.0.0.1" and accepting
TCP/IP connections on port 5432?
what also complicates things possibly, is i cannot find anywhere pg_hba.conf ,are these even still a thing in version 10 of postgresql? i have /usr/lib/postgresql/10 but no config files.. and ive also searched the machine.. nothing found. any help would be much appreciated.
thankyou

Answer 1

The official documentation for libpqxx states that:
The connection string consists of attribute=value pairs separated by spaces, e.g. "user=john password=1x2y3z4". reference
Your connection string is:
pqxx::connection C(
"user=admin "
"hostaddr=127.0.0.1 "
"password=quest "
"dbname=qdb"
"port=8812 ");
You are missing a space after qdb, so the correct connection string is:
pqxx::connection C(
"user=admin "
"hostaddr=127.0.0.1 "
"password=quest "
"dbname=qdb "
"port=8812 ");
I just tried it and it works fine for me.
On a second hand, the following SQL statement:
W.exec0("UPDATE employee SET salary = salary*2");
Will not work, UPDATE is not supported yet by QuestDB. You can find more details about SQL support on the official documentation, here.