> For the complete documentation index, see [llms.txt](https://docs.postgresql.tw/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.postgresql.tw/client-interfaces/libpq/libpq-control.md).

# 32.11. Control Functions \#

These functions control miscellaneous details of libpq's behavior.

`PQclientEncoding` [#](#LIBPQ-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` [#](#LIBPQ-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`](libpq-control.md#LIBPQ-PQCLIENTENCODING).
````

`PQsetErrorVerbosity` [#](#LIBPQ-PQSETERRORVERBOSITY) : Determines the verbosity of messages returned by [`PQerrorMessage`](/client-interfaces/libpq/libpq-status.md#LIBPQ-PQERRORMESSAGE) and [`PQresultErrorMessage`](/client-interfaces/libpq/libpq-exec.md#LIBPQ-PQRESULTERRORMESSAGE).

````
```

typedef enum
{
    PQERRORS_TERSE,
    PQERRORS_DEFAULT,
    PQERRORS_VERBOSE,
    PQERRORS_SQLSTATE
} PGVerbosity;

PGVerbosity PQsetErrorVerbosity(PGconn *conn, PGVerbosity verbosity);
```

[`PQsetErrorVerbosity`](libpq-control.md#LIBPQ-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`](libpq-exec.md#LIBPQ-PQRESULTVERBOSEERRORMESSAGE) if you
want to print a previous error with a different verbosity.)
````

`PQsetErrorContextVisibility` [#](#LIBPQ-PQSETERRORCONTEXTVISIBILITY) : Determines the handling of `CONTEXT` fields in messages returned by [`PQerrorMessage`](/client-interfaces/libpq/libpq-status.md#LIBPQ-PQERRORMESSAGE) and [`PQresultErrorMessage`](/client-interfaces/libpq/libpq-exec.md#LIBPQ-PQRESULTERRORMESSAGE).

````
```

typedef enum
{
    PQSHOW_CONTEXT_NEVER,
    PQSHOW_CONTEXT_ERRORS,
    PQSHOW_CONTEXT_ALWAYS
} PGContextVisibility;

PGContextVisibility PQsetErrorContextVisibility(PGconn *conn, PGContextVisibility show_context);
```

[`PQsetErrorContextVisibility`](libpq-control.md#LIBPQ-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`](libpq-exec.md#LIBPQ-PQRESULTVERBOSEERRORMESSAGE) if you
want to print a previous error with a different display mode.)
````

`PQtrace` [#](#LIBPQ-PQTRACE) : 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 54.7](../../internals/protocol/protocol-message-formats.md).

### 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.
````

`PQsetTraceFlags` [#](#LIBPQ-PQSETTRACEFLAGS) : 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`.
````

`PQuntrace` [#](#LIBPQ-PQUNTRACE) : Disables tracing started by [`PQtrace`](#LIBPQ-PQTRACE).

````
```

void PQuntrace(PGconn *conn);
```
````

***

原文：[PostgreSQL 18.6 Documentation](https://www.postgresql.org/docs/18/libpq-control.html)（英文原文，待翻譯）


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