Question

Context

I’ve just installed postgres 9.1.4 on Lion, and i would like to write a simple client in C (libpq) to connect to PG databases.

psql -l says that there is a database named mydb owned by postgresDB.

psql mydb says : mydb=#

Here the little program that tries to connect to mydb :

// Server coordinates
const char * keywords[] = {"dbname", "user", NULL};
const char * values[] = {"mydb", "postgresDB", NULL};

// Check server state
analyse_PQpingParams (PQpingParams (keywords, values, 0));

// Connect to the database
PGconn * conn; 
conn = PQconnectdbParams (keywords, values, 0);

// Check if the connection is healthy
analyse_PQstatus (PQstatus (conn));

// Clean exit
PQfinish (conn);
exit (0);

Problem

Here what the program retuns :

analyse_PQpingParams says :
------
The server is running and appears to be accepting connections.
------

analyse_PQstatus says :
------
The state returned was NULL.
------

Why is the conn object NULL ?

What the documentation says :

Note that these functions will always return a non-null object pointer, unless perhaps there is too little memory even to allocate the PGconn object. If it was a memory problem, then psql could not have connected to my db. So, the documentation doesn’t help here. Maybe elsewhere ?

Many thanks for your answers !

Pierre.

analyse_PQstatus code :

void analyse_PQstatus (int status) 
{
  cout << "\nanalyse_PQstatus says :" << endl;
  cout << "------" << endl;
  switch (status)
    {
    case CONNECTION_STARTED:
      cout << "Waiting for connection to be made." << endl;
      break;

    case CONNECTION_MADE:
      cout << "Connection OK; waiting to send." << endl;
      break;

    case CONNECTION_AWAITING_RESPONSE:
      cout << "Waiting for a response from the server." << endl;
      break;

    case CONNECTION_AUTH_OK:
      cout << "Received authentication; waiting for backend start-up to finish." << endl;
      break;

    case CONNECTION_SSL_STARTUP:
      cout << "Negotiating SSL encryption." << endl;
      break;

    case CONNECTION_SETENV:
      cout << "Negotiating environment-driven parameter settings." << endl;
      break;
    case 0 :
      cout << "The state returned was NULL" << endl;
      break;
    default :
      cout << "could not analyse this status code : " << status << endl;
    } 
    cout << "------\n" << endl;
} 

Answer 1

Can you show the analyse_PQstatus function? Are you really finding that conn is NULL or that the result of PQstatus(conn) (which is what you are passing to the function) is 0, i.e. CONNECTION_OK?