pqxx Namespace Reference

The home of all libpqxx classes, functions, templates, etc. More...

Namespaces
namespace	internal
	Internal items for libpqxx' own use. Do not use these yourself.
namespace	prepare

Classes
struct	argument_error
	Invalid argument passed to libpqxx, similar to std::invalid_argument. More...
class	array
	An SQL array received from the database. More...
class	array_parser
	Low-level parser for C++ arrays. More...
class	basic_fieldstream
	Input stream that gets its data from a result field. More...
class	basic_ilostream
	Input stream that gets its data from a large object. More...
class	basic_lostream
	Stream that reads and writes a large object. More...
class	basic_olostream
	Output stream that writes data back to a large object. More...
class	binarystring
	Binary data corresponding to PostgreSQL's "BYTEA" binary-string type. More...
class	blob
struct	broken_connection
	Exception class for lost or failed backend connection. More...
struct	byte_char_traits
	Custom std::char_trast if the compiler does not provide one. More...
struct	check_violation
class	connecting
	An ongoing, non-blocking stepping stone to a connection. More...
class	connection
	Connection to a database. More...
class	const_result_iterator
	Iterator for rows in a result. Use as result::const_iterator. More...
class	const_reverse_result_iterator
	Reverse iterator for result. Use as result::const_reverse_iterator. More...
class	const_reverse_row_iterator
	Reverse iterator for a row. Use as row::const_reverse_iterator. More...
class	const_row_iterator
	Iterator for fields in a row. Use as row::const_iterator. More...
struct	conversion_error
	Value conversion failed, e.g. when converting "Hello" to int. More...
struct	conversion_overrun
	Could not convert value to string: not enough buffer space. More...
class	cursor_base
	Common definitions for cursor types. More...
struct	data_exception
	Error in data provided to SQL statement. More...
class	dbtransaction
	Abstract transaction base class: bracket transactions on the database. More...
struct	deadlock_detected
	The ongoing transaction has deadlocked. Retrying it may help. More...
struct	disk_full
class	errorhandler
class	exclusive_bound
	An exclusive boundary value to a pqxx::range. More...
struct	failure
	Run-time failure encountered by libpqxx, similar to std::runtime_error. More...
struct	feature_not_supported
	Database feature not supported in current setup. More...
class	field
	Reference to a field in a result set. More...
class	field_streambuf
struct	forbidden_conversion
	String traits for a forbidden type conversion. More...
struct	foreign_key_violation
struct	from_query_t
	Marker for stream_from constructors: "stream from query.". More...
struct	from_table_t
	Marker for stream_from constructors: "stream from table.". More...
struct	has_generic_char_traits
struct	has_generic_char_traits< TYPE, std::void_t< decltype(std::char_traits< TYPE >::eof)> >
struct	in_doubt_error
	"Help, I don't know whether transaction was committed successfully!" More...
class	inclusive_bound
	An inclusive boundary value to a pqxx::range. More...
struct	insufficient_privilege
struct	insufficient_resources
	Resource shortage on the server. More...
struct	integrity_constraint_violation
struct	internal_error
	Internal error in libpqxx library. More...
struct	invalid_cursor_name
struct	invalid_cursor_state
struct	invalid_sql_statement_name
class	largeobject
	Identity of a large object. More...
class	largeobject_streambuf
	Streambuf to use large objects in standard I/O streams. More...
class	largeobjectaccess
	Accessor for large object's contents. More...
struct	no_bound
	An unlimited boundary value to a pqxx::range. More...
struct	no_null
	Nullness traits describing a type which does not have a null value. More...
class	nontransaction
	Simple "transaction" class offering no transactional integrity. More...
struct	not_null_violation
struct	notification
	An incoming notification. More...
class	notification_receiver
struct	nullness
	Traits describing a type's "null value," if any. More...
struct	nullness< binarystring >
struct	nullness< bytes >
struct	nullness< bytes_view >
struct	nullness< char * >
struct	nullness< char const * >
struct	nullness< char[N]>
struct	nullness< ENUM, std::enable_if_t< std::is_enum_v< ENUM > > >
	Nullness: Enums do not have an inherent null value. More...
struct	nullness< range< TYPE > >
	A range type does not have an innate null value. More...
struct	nullness< std::array< T, N > >
struct	nullness< std::monostate >
struct	nullness< std::nullopt_t >
struct	nullness< std::nullptr_t >
struct	nullness< std::optional< T > >
struct	nullness< std::shared_ptr< T > >
struct	nullness< std::string >
struct	nullness< std::string_view >
	There's no real null for std::string_view. More...
struct	nullness< std::stringstream >
struct	nullness< std::unique_ptr< T > >
struct	nullness< std::variant< T... > >
struct	nullness< std::vector< T, Args... > >
struct	nullness< T, std::enable_if_t< std::is_arithmetic_v< T > > >
	The built-in arithmetic types do not have inherent null values. More...
struct	nullness< zview >
struct	out_of_memory
class	params
	Build a parameter list for a parameterised or prepared statement. More...
class	pipeline
	Processes several queries in FIFO manner, optimized for high throughput. More...
class	placeholders
	Generate parameter placeholders for use in an SQL statement. More...
struct	plpgsql_error
	PL/pgSQL error. More...
struct	plpgsql_no_data_found
struct	plpgsql_raise
	Exception raised in PL/pgSQL procedure. More...
struct	plpgsql_too_many_rows
class	prepped
	A string that is the name of a prepared statement. More...
struct	protocol_violation
	Exception class for micommunication with the server. More...
class	quiet_errorhandler
class	range
	A C++ equivalent to PostgreSQL's range types. More...
class	range_bound
	A range boundary value. More...
struct	range_error
	Something is out of range, similar to std::out_of_range. More...
struct	restrict_violation
class	result
	Result set containing data returned by a query or command. More...
class	row
	Reference to one row in a result. More...
struct	serialization_failure
	Transaction failed to serialize. Please retry it. More...
class	sql_error
	Exception class for failed queries. More...
class	stateless_cursor
	"Stateless cursor" class: easy API for retrieving parts of result sets More...
struct	statement_completion_unknown
	We can't tell whether our last statement succeeded. More...
class	stream_from
	Stream data from the database. More...
class	stream_query
class	stream_to
	Efficiently write data directly to a database table. More...
struct	string_traits
	Traits class for use in string conversions. More...
struct	string_traits< binarystring >
	String conversion traits for binarystring. More...
struct	string_traits< bool >
struct	string_traits< bytes >
struct	string_traits< bytes_view >
struct	string_traits< char * >
	String traits for non-const C-style string ("pointer to char"). More...
struct	string_traits< char >
	You cannot convert a char to/from SQL. More...
struct	string_traits< char const * >
	String traits for C-style string ("pointer to char const"). More...
struct	string_traits< char[N]>
	String traits for C-style string constant ("pointer to array of char"). More...
struct	string_traits< double >
struct	string_traits< float >
struct	string_traits< int >
struct	string_traits< long >
struct	string_traits< long double >
struct	string_traits< long long >
struct	string_traits< pqxx::internal::encoding_group >
struct	string_traits< range< TYPE > >
	String conversions for a range type. More...
struct	string_traits< short >
struct	string_traits< signed char >
	You cannot convert a signed char to/from SQL. More...
struct	string_traits< std::array< T, N > >
struct	string_traits< std::byte >
	You cannot convert a std::byte to/from SQL. More...
struct	string_traits< std::monostate >
struct	string_traits< std::nullopt_t >
struct	string_traits< std::nullptr_t >
struct	string_traits< std::optional< T > >
struct	string_traits< std::shared_ptr< T > >
struct	string_traits< std::string >
struct	string_traits< std::string_view >
	String traits for string_view. More...
struct	string_traits< std::stringstream >
struct	string_traits< std::unique_ptr< T, Args... > >
struct	string_traits< std::variant< T... > >
struct	string_traits< std::vector< T, Args... > >
struct	string_traits< unsigned >
struct	string_traits< unsigned char >
	You cannot convert an unsigned char to/from SQL. More...
struct	string_traits< unsigned long >
struct	string_traits< unsigned long long >
struct	string_traits< unsigned short >
struct	string_traits< zview >
	String traits for zview. More...
class	subtransaction
	"Transaction" nested within another transaction More...
struct	syntax_error
struct	thread_safety_model
	Descriptor of library's thread-safety model. More...
struct	too_many_connections
class	transaction_base
	Interface definition (and common code) for "transaction" classes. More...
class	transaction_focus
	Base class for things that monopolise a transaction's attention. More...
struct	transaction_rollback
	The backend saw itself forced to roll back the ongoing transaction. More...
struct	undefined_column
struct	undefined_function
struct	undefined_table
struct	unexpected_null
	Could not convert null value: target type does not support null. More...
struct	unexpected_rows
	Query returned an unexpected number of rows. More...
struct	unique_violation
struct	usage_error
	Error in usage of libpqxx library, similar to std::logic_error. More...
struct	variable_set_to_null
	The caller attempted to set a variable to null, which is not allowed. More...
class	zview
	Marker-type wrapper: zero-terminated std::string_view. More...

Typedefs
using	table_path = std::initializer_list< std::string_view >
	Representation of a PostgreSQL table path.
using	connection_base = connection
using	fieldstream = basic_fieldstream< char >
using	oid = unsigned int
	PostgreSQL database row identifier.
using	ilostream = basic_ilostream< char >
using	olostream = basic_olostream< char >
using	lostream = basic_lostream< char >
using	result_size_type = int
	Number of rows in a result set.
using	result_difference_type = int
	Difference between result sizes.
using	row_size_type = int
	Number of fields in a row of database data.
using	row_difference_type = int
	Difference between row sizes.
using	field_size_type = std::size_t
	Number of bytes in a field of database data.
using	large_object_size_type = int64_t
	Number of bytes in a large object.
template<typename TYPE >
using	strip_t = std::remove_cv_t< std::remove_reference_t< TYPE > >
	Remove any constness, volatile, and reference-ness from a type.
template<typename CONTAINER >
using	value_type = strip_t< decltype(*std::begin(std::declval< CONTAINER >()))>
	The type of a container's elements.
using	bytes = std::conditional< has_generic_bytes_char_traits, std::basic_string< std::byte >, std::basic_string< std::byte, byte_char_traits > >::type
	Type alias for a container containing bytes.
using	bytes_view = std::conditional< has_generic_bytes_char_traits, std::basic_string_view< std::byte >, std::basic_string_view< std::byte, byte_char_traits > >::type
	Type alias for a view of bytes.

Enumerations
enum	skip_init : int { nothing , openssl , crypto }
	Flags for skipping initialisation of SSL-related libraries. More...
enum class	error_verbosity : int { terse = 0 , normal = 1 , verbose = 2 }
	Error verbosity levels.
enum class	write_policy { read_only , read_write }
	Should a transaction be read-only, or read-write? More...
enum	isolation_level { read_committed , repeatable_read , serializable }
	Transaction isolation levels. More...
enum class	format : int { text = 0 , binary = 1 }
	Format code: is data text or binary? More...

Functions
template<typename... T>
void	parse_composite (pqxx::internal::encoding_group enc, std::string_view text, T &...fields)
	Parse a string representation of a value of a composite type.
template<typename... T>
void	parse_composite (std::string_view text, T &...fields)
	Parse a string representation of a value of a composite type.
template<typename... T>
std::size_t	composite_size_buffer (T const &...fields) noexcept
	Estimate the buffer size needed to represent a value of a composite type.
template<typename... T>
char *	composite_into_buf (char *begin, char *end, T const &...fields)
	Render a series of values as a single composite SQL value.
template<skip_init... SKIP>
void	skip_init_ssl () noexcept
	Control initialisation of OpenSSL and libcrypto libraries.
std::string PQXX_LIBEXPORT	encrypt_password (char const user[], char const password[])
	Encrypt a password.
std::string	encrypt_password (zview user, zview password)
	Encrypt password.
template<>
bool	field::to< std::string > (std::string &obj) const
template<>
bool	field::to< std::string > (std::string &obj, std::string const &default_value) const
template<>
bool	field::to< std::string_view > (std::string_view &obj) const
template<>
bool	field::to< std::string_view > (std::string_view &obj, std::string_view const &default_value) const
template<>
std::string_view	field::as< std::string_view > () const
template<>
std::string_view	field::as< std::string_view > (std::string_view const &default_value) const
template<typename CHAR >
std::basic_ostream< CHAR > &	operator<< (std::basic_ostream< CHAR > &s, field const &value)
	Write a result field to any type of stream.
template<typename T >
T	from_string (field const &value)
	Convert a field's value to type T.
template<>
std::nullptr_t	from_string< std::nullptr_t > (field const &value)
	Convert a field's value to nullptr_t.
template<>
PQXX_LIBEXPORT std::string	to_string (field const &value)
	Convert a field to a string.
template<typename T >
constexpr format	param_format (std::optional< T > const &value)
template<typename... Args>
constexpr format	param_format (std::variant< Args... > const &value)
template<typename T >
T	from_string (std::stringstream const &text)
template<typename T , typename... Args>
format	param_format (std::unique_ptr< T, Args... > const &value)
template<typename T >
format	param_format (std::shared_ptr< T > const &value)
template<>
constexpr format	param_format (bytes const &)
template<>
constexpr format	param_format (bytes_view const &)
template<typename T , typename... Args>
constexpr format	param_format (std::vector< T, Args... > const &)
	We don't know how to pass array params in binary format, so pass as text.
template<typename... Args>
constexpr format	param_format (std::vector< std::byte, Args... > const &)
	A std::vector<std::byte> is a binary string. Other vectors are not.
template<typename T , typename... Args, Args... args>
constexpr format	param_format (std::array< T, args... > const &)
	We don't know how to pass array params in binary format, so pass as text.
template<typename... Args, Args... args>
constexpr format	param_format (std::array< std::byte, args... > const &)
	An array of std::byte is a binary string.
template<typename T >
std::string	to_string (T const &value)
template<>
std::string	to_string (float const &value)
template<>
std::string	to_string (double const &value)
template<>
std::string	to_string (long double const &value)
template<>
std::string	to_string (std::stringstream const &value)
template<typename T >
void	into_string (T const &value, std::string &out)
const_result_iterator	operator+ (result::difference_type o, const_result_iterator const &i)
const_reverse_result_iterator	operator+ (result::difference_type n, const_reverse_result_iterator const &i)
const_row_iterator	operator+ (const_row_iterator::difference_type o, const_row_iterator const &i) noexcept
template<typename ITER , typename ACCESS >
std::string	separated_list (std::string_view sep, ITER begin, ITER end, ACCESS access)
	Represent sequence of values as a string, joined by a given separator.
template<typename ITER >
std::string	separated_list (std::string_view sep, ITER begin, ITER end)
	Render sequence as a string, using given separator between items.
template<typename CONTAINER >
auto	separated_list (std::string_view sep, CONTAINER const &c) -> typename std::enable_if<(not std::is_void< decltype(std::begin(c))>::value and not std::is_void< decltype(std::end(c))>::value), std::string >::type
	Render items in a container as a string, using given separator.
template<typename TUPLE , std::size_t INDEX = 0, typename ACCESS , typename std::enable_if<(INDEX==std::tuple_size< TUPLE >::value - 1), int >::type = 0>
std::string	separated_list (std::string_view, TUPLE const &t, ACCESS const &access)
	Render items in a tuple as a string, using given separator.
template<typename TUPLE , std::size_t INDEX = 0, typename std::enable_if<(INDEX<=std::tuple_size< TUPLE >::value), int >::type = 0>
std::string	separated_list (std::string_view sep, TUPLE const &t)
template<typename TYPE >
void	oops_forbidden_conversion () noexcept
	Nonexistent function to indicate a disallowed type conversion.
template<>
std::string_view	transaction_base::query_value< std::string_view > (zview query, std::string_view desc)=delete
	Forbidden specialisation: underlying buffer immediately goes out of scope.
template<typename TRANSACTION_CALLBACK >
auto	perform (TRANSACTION_CALLBACK &&callback, int attempts=3) -> std::invoke_result_t< TRANSACTION_CALLBACK >
	Simple way to execute a transaction with automatic retry.
template<typename... T>
constexpr void	ignore_unused (T &&...) noexcept
	Suppress compiler warning about an unused item.
template<typename TO , typename FROM >
TO	check_cast (FROM value, std::string_view description)
	Cast a numeric value to another type, or throw if it underflows/overflows.
PQXX_PRIVATE void	check_version () noexcept
PQXX_LIBEXPORT thread_safety_model	describe_thread_safety ()
	Describe thread safety available in this build.
template<typename TYPE >
bytes_view	binary_cast (TYPE const &data)
	Cast binary data to a type that libpqxx will recognise as binary.
template<typename CHAR , typename SIZE >
bytes_view	binary_cast (CHAR const *data, SIZE size)
	Construct a type that libpqxx will recognise as binary.
constexpr zview	operator""_zv (char const str[], std::size_t len) noexcept
	Support zview literals.

Variables
template<>
std::string_view const	type_name< ExecStatusType > { "ExecStatusType" }
template<>
constexpr bool	is_unquoted_safe< short > {true}
template<>
constexpr bool	is_unquoted_safe< unsigned short > {true}
template<>
constexpr bool	is_unquoted_safe< int > {true}
template<>
constexpr bool	is_unquoted_safe< unsigned > {true}
template<>
constexpr bool	is_unquoted_safe< long > {true}
template<>
constexpr bool	is_unquoted_safe< unsigned long > {true}
template<>
constexpr bool	is_unquoted_safe< long long > {true}
template<>
constexpr bool	is_unquoted_safe< unsigned long long > {true}
template<>
constexpr bool	is_unquoted_safe< float > {true}
template<>
constexpr bool	is_unquoted_safe< double > {true}
template<>
constexpr bool	is_unquoted_safe< long double > {true}
template<>
constexpr bool	is_unquoted_safe< bool > {true}
template<typename TYPE >
std::string const	type_name {internal::demangle_type_name(typeid(TYPE).name())}
	A human-readable name for a type, used in error messages and such.
constexpr from_table_t	from_table
	Pass this to a stream_from constructor to stream table contents.
constexpr from_query_t	from_query
	Pass this to a stream_from constructor to stream query results.
constexpr bool	has_generic_bytes_char_traits
constexpr oid	oid_none {0}
	The "null" oid.

Detailed Description

The home of all libpqxx classes, functions, templates, etc.

Handling of SQL arrays.

Copyright (c) 2000-2025, Jeroen T. Vermeulen.

See COPYING for copyright license. If you did not receive a file called COPYING with this source code, please notify the distributor of this mistake, or contact the author.

Implementation of the pqxx::result class and support classes.

pqxx::result represents the set of result rows from a database query

Copyright (c) 2000-2025, Jeroen T. Vermeulen.

See COPYING for copyright license. If you did not receive a file called COPYING with this source code, please notify the distributor of this mistake, or contact the author.

Internal string encodings support for libpqxx

Copyright (c) 2000-2025, Jeroen T. Vermeulen.

See COPYING for copyright license. If you did not receive a file called COPYING with this source code, please notify the distributor of this mistake, or contact the author.

Result loops.

Copyright (c) 2000-2025, Jeroen T. Vermeulen.

See COPYING for copyright license. If you did not receive a file called COPYING with this source code, please notify the distributor of this mistake, or contact the author.

Stream iterators.

Copyright (c) 2000-2025, Jeroen T. Vermeulen.

See COPYING for copyright license. If you did not receive a file called COPYING with this source code, please notify the distributor of this mistake, or contact the author.

Transaction focus: types which monopolise a transaction's attention.

Copyright (c) 2000-2025, Jeroen T. Vermeulen.

See COPYING for copyright license. If you did not receive a file called COPYING with this source code, please notify the distributor of this mistake, or contact the author.

---

Class Documentation

pqxx::from_query_t

struct pqxx::from_query_t

Marker for stream_from constructors: "stream from query.".

Deprecated:

Use stream_from::query() instead.

pqxx::from_table_t

struct pqxx::from_table_t

Marker for stream_from constructors: "stream from table.".

Deprecated:

Use stream_from::table() instead.

pqxx::notification

struct pqxx::notification

An incoming notification.

PostgreSQL extends SQL with a "message bus" using the LISTEN and NOTIFY commands. In libpqxx you use connection::listen() and (optionally) transaction_base::notify().

When you receive a notification for which you have been listening, your handler receives it in the form of a notification object.

Warning

These structs are meant for extremely short lifespans: the fields reference memory that may become invalid as soon as your handler has been called.

Collaboration diagram for pqxx::notification:

Class Members
int	backend_pid	Process ID of the backend that sent the notification. This can be useful in situations where a multiple clients are listening on the same channel, and also send notifications on it. In those situations, it often makes sense for a client to ignore its own incoming notifications, but handle all others on the same channel in some way. To check for that, compare this process ID to the return value of the connection's backendpid().
zview	channel	Channel name. The notification logic will only pass the notification to a handler which was registered to listen on this exact name.
connection &	conn	The connection which received the notification. There will be no backend transaction active on the connection when your handler gets called, but there may be a nontransaction. (This is a special transaction type in libpqxx which does not start a transaction on the backend.)
zview	payload	Optional payload text. If the notification did not carry a payload, the string will be empty.

pqxx::stream_query

class pqxx::stream_query

template<typename... TYPE>
class pqxx::stream_query< TYPE >

pqxx::thread_safety_model

struct pqxx::thread_safety_model

Descriptor of library's thread-safety model.

This describes what the library knows about various risks to thread-safety.

Class Members
string	description	A human-readable description of any thread-safety issues.
bool	safe_kerberos = false	Is Kerberos thread-safe? Warning Is currently always false. If your application uses Kerberos, all accesses to libpqxx or Kerberos must be serialized. Confine their use to a single thread, or protect it with a global lock.
bool	safe_libpq = false	Is the underlying libpq build thread-safe?

Typedef Documentation

connection_base

using pqxx::connection_base = typedef connection

Deprecated:

Old base class for connection. They are now the same class.

fieldstream

using pqxx::fieldstream = typedef basic_fieldstream<char>

Deprecated:

Read a field using field::as<...>() or field::c_str().

strip_t

template<typename TYPE >

using pqxx::strip_t = typedef std::remove_cv_t<std::remove_reference_t<TYPE> >

Remove any constness, volatile, and reference-ness from a type.

Deprecated:

In C++20 we'll replace this with std::remove_cvref.

table_path

using pqxx::table_path = typedef std::initializer_list<std::string_view>

Representation of a PostgreSQL table path.

A "table path" consists of a table name, optionally prefixed by a schema name, which in turn is optionally prefixed by a database name.

A minimal example of a table path would be {mytable}. But a table path may also take the forms {myschema,mytable} or {mydb,myschema,mytable}.

value_type

template<typename CONTAINER >

using pqxx::value_type = typedef strip_t<decltype(*std::begin(std::declval<CONTAINER>()))>

The type of a container's elements.

At the time of writing there's a similar thing in std::experimental, which we may or may not end up using for this.

Enumeration Type Documentation

format

enum class pqxx::format : int

strong

Format code: is data text or binary?

Binary-compatible with libpq's format codes.

isolation_level

enum pqxx::isolation_level

Transaction isolation levels.

These are as defined in the SQL standard. But there are a few notes specific to PostgreSQL.

First, postgres does not support "read uncommitted." The lowest level you can get is "read committed," which is better. PostgreSQL is built on the MVCC paradigm, which guarantees "read committed" isolation without any additional performance overhead, so there was no point in providing the lower level.

Second, "repeatable read" also makes more isolation guarantees than the standard requires. According to the standard, this level prevents "dirty reads" and "nonrepeatable reads," but not "phantom reads." In postgres, it actually prevents all three.

Third, "serializable" is only properly supported starting at postgres 9.1. If you request "serializable" isolation on an older backend, you will get the same isolation as in "repeatable read." It's better than the "repeatable read" defined in the SQL standard, but not a complete implementation of the standard's "serializable" isolation level.

In general, a lower isolation level will allow more surprising interactions between ongoing transactions, but improve performance. A higher level gives you more protection from subtle concurrency bugs, but sometimes it may not be possible to complete your transaction without avoiding paradoxes in the data. In that case a transaction may fail, and the application will have to re-do the whole thing based on the latest state of the database. (If you want to retry your code in that situation, have a look at the transactor framework.)

Study the levels and design your application with the right level in mind.

skip_init

enum pqxx::skip_init : int

Flags for skipping initialisation of SSL-related libraries.

When a running process makes its first SSL connection to a database through libpqxx, libpq automatically initialises the OpenSSL and libcrypto libraries. But there are scenarios in which you may want to suppress that.

This enum is a way to express this. Pass values of this enum to pqxx::skip_init_ssl as template arguments.

Enumerator
nothing	A do-nothing flag that does not affect anything.
openssl	Skip initialisation of OpenSSL library.
crypto	Skip initialisation of libcrypto.

write_policy

enum class pqxx::write_policy

strong

Should a transaction be read-only, or read-write?

No, this is not an isolation level. So it really doesn't belong here. But it's not really worth a separate header.

Function Documentation

binary_cast() [1/2]

template<typename CHAR , typename SIZE >

bytes_view pqxx::binary_cast	(	CHAR const *	data,
		SIZE	size
	)

Construct a type that libpqxx will recognise as binary.

Takes a data pointer and a size, without being too strict about their types, and constructs a pqxx::bytes_view pointing to the same data.

This makes it a little easier to turn binary data, in whatever form you happen to have it, into binary data as libpqxx understands it.

binary_cast() [2/2]

template<typename TYPE >

bytes_view pqxx::binary_cast

(

TYPE const &

data

)

Cast binary data to a type that libpqxx will recognise as binary.

There are many different formats for storing binary data in memory. You may have yours as a std::string, or a std::vector<uchar_t>, or one of many other types.

But for libpqxx to recognise your data as binary, it needs to be a pqxx::bytes, or a pqxx::bytes_view; or in C++20 or better, any contiguous block of std::byte.

Use binary_cast as a convenience helper to cast your data as a pqxx::bytes_view.

Warning

There are two things you should be aware of! First, the data must be contiguous in memory. In C++20 the compiler will enforce this, but in C++17 it's your own problem. Second, you must keep the object where you store the actual data alive for as long as you might use this function's return value.

check_cast()

template<typename TO , typename FROM >

TO pqxx::check_cast ( FROM  value, std::string_view  description  )

inline

Cast a numeric value to another type, or throw if it underflows/overflows.

Both types must be arithmetic types, and they must either be both integral or both floating-point types.

check_version()

PQXX_PRIVATE void pqxx::check_version ( )

inlinenoexcept

Check library version at link time.

Ensures a failure when linking an application against a radically different libpqxx version than the one against which it was compiled.

Sometimes application builds fail in unclear ways because they compile using headers from libpqxx version X, but then link against libpqxx binary version Y. A typical scenario would be one where you're building against a libpqxx which you have built yourself, but a different version is installed on the system.

The check_library_version template is declared for any library version, but only actually defined for the version of the libpqxx binary against which the code is linked.

If the library binary is a different version than the one declared in these headers, then this call will fail to link: there will be no definition for the function with these exact template parameter values. There will be a definition, but the version in the parameter values will be different.

composite_into_buf()

template<typename... T>

char * pqxx::composite_into_buf ( char *  begin, char *  end, T const &...  fields  )

inline

Render a series of values as a single composite SQL value.

Warning

This code is still experimental. Use with care.

You may use this as a helper while implementing your own string_traits for a composite type.

composite_size_buffer()

template<typename... T>

std::size_t pqxx::composite_size_buffer ( T const &...  fields )

inlinenoexcept

Estimate the buffer size needed to represent a value of a composite type.

Returns a conservative estimate.

encrypt_password() [1/2]

std::string PQXX_LIBEXPORT pqxx::encrypt_password	(	char const	user[],
		char const	password[]
	)

Encrypt a password.

Deprecated:

Use connection::encrypt_password instead.

encrypt_password() [2/2]

std::string pqxx::encrypt_password ( zview  user, zview  password  )

inline

Encrypt password.

Deprecated:

Use connection::encrypt_password instead.

from_string()

template<typename T >

T pqxx::from_string ( field const &  value )

inline

Convert a field's value to type T.

Unlike the "regular" from_string, this knows how to deal with null values.

from_string< std::nullptr_t >()

template<>

std::nullptr_t pqxx::from_string< std::nullptr_t > ( field const &  value )

inline

Convert a field's value to nullptr_t.

Yes, you read that right. This conversion does nothing useful. It always returns nullptr.

Except... what if the field is not null? In that case, this throws conversion_error.

oops_forbidden_conversion()

template<typename TYPE >

void pqxx::oops_forbidden_conversion ( )

noexcept

Nonexistent function to indicate a disallowed type conversion.

There is no implementation for this function, so any reference to it will fail to link. The error message will mention the function name and its template argument, as a deliberate message to an application developer that their code is attempting to use a deliberately unsupported conversion.

There are some C++ types that you may want to convert to or from SQL values, but which libpqxx deliberately does not support. Take char for example: we define no conversions for that type because it is not inherently clear whether whether the corresponding SQL type should be a single-character string, a small integer, a raw byte value, etc. The intention could differ from one call site to the next.

If an application attempts to convert these types, we try to make sure that the compiler will issue an error involving this function name, and mention the type, as a hint as to the reason.

operator""_zv()

constexpr zview pqxx::operator""_zv ( char const  str[], std::size_t  len  )

constexprnoexcept

Support zview literals.

You can "import" this selectively into your namespace, without pulling in all of the pqxx namespace:

using pqxx::operator"" _zv;

operator<<()

template<typename CHAR >

std:: basic_ostream< CHAR > & pqxx::operator<< ( std::basic_ostream< CHAR > &  s, field const &  value  )

inline

Write a result field to any type of stream.

Deprecated:

The C++ streams library is not great to work with. In particular, error handling is easy to get wrong. So you're probably better off doing this by hand.

This can be convenient when writing a field to an output stream. More importantly, it lets you write a field to e.g. a stringstream which you can then use to read, format and convert the field in ways that to() does not support.

Example: parse a field into a variable of the nonstandard long long type.

extern result R;
long long L;
stringstream S;
 
// Write field's string into S
S << R[0][0];
 
// Parse contents of S into L
S >> L;

parse_composite() [1/2]

template<typename... T>

void pqxx::parse_composite ( pqxx::internal::encoding_group  enc, std::string_view  text, T &...  fields  )

inline

Parse a string representation of a value of a composite type.

Warning

This code is still experimental. Use with care.

You may use this as a helper while implementing your own string_traits for a composite type.

This function interprets text as the string representation of a value of some composite type, and sets each of fields to the respective values of its fields. The field types must be copy-assignable.

The number of fields must match the number of fields in the composite type, and there must not be any other text in the input. The function is meant to handle any value string that the backend can produce, but not necessarily every valid alternative spelling.

Fields in composite types can be null. When this happens, the C++ type of the corresponding field reference must be of a type that can handle nulls. If you are working with a type that does not have an inherent null value, such as e.g. int, consider using std::optional.

parse_composite() [2/2]

template<typename... T>

void pqxx::parse_composite ( std::string_view  text, T &...  fields  )

inline

Parse a string representation of a value of a composite type.

Warning

This version only works for UTF-8 and single-byte encodings.

For proper encoding support, use the composite-type support in the field class.

perform()

template<typename TRANSACTION_CALLBACK >

auto pqxx::perform ( TRANSACTION_CALLBACK &&  callback, int  attempts = 3  ) -> std::invoke_result_t<TRANSACTION_CALLBACK>

inline

Simple way to execute a transaction with automatic retry.

Executes your transaction code as a callback. Repeats it until it completes normally, or it throws an error other than the few libpqxx-generated exceptions that the framework understands, or after a given number of failed attempts, or if the transaction ends in an "in-doubt" state.

(An in-doubt state is one where libpqxx cannot determine whether the server finally committed a transaction or not. This can happen if the network connection to the server is lost just while we're waiting for its reply to a "commit" statement. The server may have completed the commit, or not, but it can't tell you because there's no longer a connection.

Using this still takes a bit of care. If your callback makes use of data from the database, you'll probably have to query that data within your callback. If the attempt to perform your callback fails, and the framework tries again, you'll be in a new transaction and the data in the database may have changed under your feet.

Also be careful about changing variables or data structures from within your callback. The run may still fail, and perhaps get run again. The ideal way to do it (in most cases) is to return your result from your callback, and change your program's data state only after perform completes successfully.

Parameters

callback	Transaction code that can be called with no arguments.
attempts	Maximum number of times to attempt performing callback. Must be greater than zero.

Returns

Whatever your callback returns.

separated_list()

template<typename ITER , typename ACCESS >

std::string pqxx::separated_list ( std::string_view  sep, ITER  begin, ITER  end, ACCESS  access  )

inline

Represent sequence of values as a string, joined by a given separator.

Use this to turn e.g. the numbers 1, 2, and 3 into a string "1, 2, 3".

Parameters

sep	separator string (to be placed between items)
begin	beginning of items sequence
end	end of items sequence
access	functor defining how to dereference sequence elements

skip_init_ssl()

template<skip_init... SKIP>

void pqxx::skip_init_ssl ( )

inlinenoexcept

Control initialisation of OpenSSL and libcrypto libraries.

By default, libpq initialises the openssl and libcrypto libraries when your process first opens an SSL connection to a database. But this may not be what you want: perhaps your application (or some other library it uses) already initialises one or both of these libraries.

Call this function to stop libpq from initialising one or the other of these. Pass as arguments each of the skip_init flags for which of the libraries whose initialisation you want to prevent.

Warning

Each call to this function overwrites the effects of any previous call. So if you make one call to skip OpenSSL initialisation, and then another to skip libcrypto initialisation, the first call will do nothing.

Examples:

• To let libpq initialise libcrypto but not OpenSSL: skip_init_ssl<pqxx::skip_init::openssl>();
• To let libpq know that it should not initialise either:

  skip_init_ssl<pqxx::skip_init::openssl, pqxx::skip_init::crypto>();

• To say explicitly that you want libpq to initialise both: skip_init_ssl<pqxx::skip_init::nothing>();

Variable Documentation

from_query

constexpr from_query_t pqxx::from_query

constexpr

Pass this to a stream_from constructor to stream query results.

Deprecated:

Use transaction_base::stream instead of stream_from.

from_table

constexpr from_table_t pqxx::from_table

constexpr

Pass this to a stream_from constructor to stream table contents.

Deprecated:

Use transaction_base::stream instead of stream_from.

has_generic_bytes_char_traits

constexpr bool pqxx::has_generic_bytes_char_traits

inlineconstexpr

Initial value:

=
  has_generic_char_traits<std::byte>::value

type_name

template<typename TYPE >

std::string const pqxx::type_name {internal::demangle_type_name(typeid(TYPE).name())}

A human-readable name for a type, used in error messages and such.

Actually this may not always be very user-friendly. It uses std::type_info::name(). On gcc-like compilers we try to demangle its output. Visual Studio produces human-friendly names out of the box.

This variable is not inline. Inlining it gives rise to "memory leak" warnings from asan, the address sanitizer, possibly from use of std::type_info::name.