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30.9. Control Functions

These functions control miscellaneous details of libpq's behavior.


Returns the client encoding.

      int PQclientEncoding(const PGconn *conn);

Note that it returns the encoding ID, not a symbolic string such as EUC_JP. To convert an encoding ID to an encoding name, you can use:

char *pg_encoding_to_char(int encoding_id);

Sets the client encoding.

      int PQsetClientEncoding(PGconn *conn, const char *encoding);

conn is a connection to the server, and encoding is the encoding you want to use. If the function successfully sets the encoding, it returns 0, otherwise -1. The current encoding for this connection can be determined by using PQclientEncoding.


Determines the verbosity of messages returned by PQerrorMessage and PQresultErrorMessage.

      typedef enum {
      } PGVerbosity;

      PGVerbosity PQsetErrorVerbosity(PGconn *conn, PGVerbosity verbosity);

PQsetErrorVerbosity sets the verbosity mode, returning the connection's previous setting. In TERSE mode, returned messages include severity, primary text, and position only; this will normally fit on a single line. The default mode produces messages that include the above plus any detail, hint, or context fields (these might span multiple lines). The VERBOSE mode includes all available fields. Changing the verbosity does not affect the messages available from already-existing PGresult objects, only subsequently-created ones.


Enables tracing of the client/server communication to a debugging file stream.

       void PQtrace(PGconn *conn, FILE *stream);

Note: On Windows, if the libpq library and an application are compiled with different flags, this function call will crash the application because the internal representation of the FILE pointers differ. Specifically, multithreaded/single-threaded, release/debug, and static/dynamic flags should be the same for the library and all applications using that library.


Disables tracing started by PQtrace.

       void PQuntrace(PGconn *conn);