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The following routines deal with making a connection to a backend from a C program.
PQsetdb Makes a new connection to a backend.
PGconn *PQsetdb(char *pghost,
char *pgport,
char *pgoptions,
char *pgtty,
char *dbName);
If any argument is NULL, then the corresponding
environment variable is checked. If the environment variable is also not set, then hardwired
defaults are used.
PQsetdb always returns a valid PGconn pointer.
The PQstatus (see below) command should be called
to ensure that a connection was properly made
before queries are sent via the connection. libpq
programmers should be careful to maintain the
PGconn abstraction. Use the accessor functions
below to get at the contents of PGconn. Avoid
directly referencing the fields of the PGconn
structure as they are subject to change in the
future.PQdb Returns the database name of the connection.
char *PQdb(PGconn *conn)
PQhost Returns the host name of the connection.
char *PQhost(PGconn *conn)
PQoptions Returns the pgoptions used in the connection.
char *PQoptions(PGconn *conn)
PQport Returns the pgport of the connection.
char *PQport(PGconn *conn)
PQtty Returns the pgtty of the connection.
char *PQtty(PGconn *conn)
PQstatus Returns the status of the connection. The status can be CONNECTION_OK or CONNECTION_BAD.
ConnStatusType *PQstatus(PGconn *conn)
PQerrorMessage Returns the error message associated with the connection
char *PQerrorMessage(PGconn* conn);
PQfinish Close the connection to the backend. Also frees memory used by the PGconn structure. The PGconn pointer should not be used after PQfinish has been called.
void PQfinish(PGconn *conn)
PQreset Reset the communication port with the backend. This function will close the IPC socket connection to the backend and attempt to reestablish a new connection to the same backend.
void PQreset(PGconn *conn)
PQtrace Enables tracing of messages passed between the frontend and the backend. The messages are echoed to the debug_port file stream.
void PQtrace(PGconn *conn,
FILE* debug_port);PQuntrace Disables tracing of messages passed between the frontend and the backend.
void PQuntrace(PGconn *conn);
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