PostgreSQL 9.6beta2 Documentation
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# 31.10. Control Functions

These functions control miscellaneous details of libpq's behavior.

`PQclientEncoding`

  Returns the client encoding.

      int PQclientEncoding(const PGconn *conn);

  Note that it returns the encoding ID, not a symbolic string such as `EUC_JP`. If unsuccessful, it returns -1. To convert an encoding ID to an encoding name, you can use:

      char *pg_encoding_to_char(int encoding_id);

`PQsetClientEncoding`

  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`.

`PQsetErrorVerbosity`

  Determines the verbosity of messages returned by `PQerrorMessage` and `PQresultErrorMessage`.

      typedef enum
      {
          PQERRORS_TERSE,
          PQERRORS_DEFAULT,
          PQERRORS_VERBOSE
      } 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. (But see `PQresultVerboseErrorMessage` if you want to print a previous error with a different verbosity.)

`PQsetErrorContextVisibility`

  Determines the handling of `CONTEXT` fields in messages returned by `PQerrorMessage` and `PQresultErrorMessage`.

      typedef enum
      {
          PQSHOW_CONTEXT_NEVER,
          PQSHOW_CONTEXT_ERRORS,
          PQSHOW_CONTEXT_ALWAYS
      } PGContextVisibility;

      PGContextVisibility PQsetErrorContextVisibility(PGconn *conn, PGContextVisibility show_context);

  `PQsetErrorContextVisibility` sets the context display mode, returning the connection's previous setting. This mode controls whether the `CONTEXT` field is included in messages (unless the verbosity setting is TERSE, in which case `CONTEXT` is never shown). The NEVER mode never includes `CONTEXT`, while ALWAYS always includes it if available. In ERRORS mode (the default), `CONTEXT` fields are included only for error messages, not for notices and warnings. Changing this mode does not affect the messages available from already-existing `PGresult` objects, only subsequently-created ones. (But see `PQresultVerboseErrorMessage` if you want to print a previous error with a different display mode.)

`PQtrace`

  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.

`PQuntrace`

  Disables tracing started by `PQtrace`.

      void PQuntrace(PGconn *conn);

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