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34.11. 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. 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);

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. The SQLSTATE mode includes only the error severity and the SQLSTATE error code, if one is available (if not, the output is like TERSE mode).

Changing the verbosity setting 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.)


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

typedef enum
} 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. The NEVER mode never includes CONTEXT, while ALWAYS always includes it if available. In ERRORS mode (the default), CONTEXT fields are included only in error messages, not in notices and warnings. (However, if the verbosity setting is TERSE or SQLSTATE, CONTEXT fields are omitted regardless of the context display mode.)

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.)


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

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

Each line consists of: an optional timestamp, a direction indicator (F for messages from client to server or B for messages from server to client), message length, message type, and message contents. Non-message contents fields (timestamp, direction, length and message type) are separated by a tab. Message contents are separated by a space. Protocol strings are enclosed in double quotes, while strings used as data values are enclosed in single quotes. Non-printable chars are printed as hexadecimal escapes. Further message-type-specific detail can be found in Section 53.7.


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.


Controls the tracing behavior of client/server communication.

void PQsetTraceFlags(PGconn *conn, int flags);

flags contains flag bits describing the operating mode of tracing. If flags contains PQTRACE_SUPPRESS_TIMESTAMPS, then the timestamp is not included when printing each message. If flags contains PQTRACE_REGRESS_MODE, then some fields are redacted when printing each message, such as object OIDs, to make the output more convenient to use in testing frameworks. This function must be called after calling PQtrace.


Disables tracing started by PQtrace.

void PQuntrace(PGconn *conn);

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