libpqxx
The C++ client library for PostgreSQL
 
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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  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...
 
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
 
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...
 
struct  data_exception
 Error in data provided to SQL statement. 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_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_streambuf
 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...
 
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  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  robusttransaction
 Slightly slower, better-fortified version of transaction. 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_query
 
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...
 
struct  syntax_error
 
struct  thread_safety_model
 Descriptor of library's thread-safety model. More...
 
struct  too_many_connections
 
class  transaction
 Standard back-end transaction, templatised on isolation level. 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 work = transaction<>
 The default transaction type.
 
using read_transaction
 Read-only transaction.
 
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
 Type alias for a container containing bytes.
 
using bytes_view
 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

class __attribute__ ((visibility("default"))) array_parser
 Low-level parser for C++ arrays.
 
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 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>
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<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>
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<typename TYPE>
TYPE from_string (std::string_view text)
 Parse a value in postgres' text format as a TYPE.
 
template<>
std::string_view from_string (std::string_view text)
 "Convert" a std::string_view to a std::string_view.
 
template<typename T>
void from_string (std::string_view text, T &value)
 Attempt to convert postgres-generated string to given built-in object.
 
template<typename TYPE>
std::string to_string (TYPE const &value)
 Convert a value to a readable string that PostgreSQL will understand.
 
template<typename... TYPE>
std::vector< std::string_view > to_buf (char *here, char const *end, TYPE... value)
 Convert multiple values to strings inside a single buffer.
 
template<typename TYPE>
void into_string (TYPE const &value, std::string &out)
 Convert a value to a readable string that PostgreSQL will understand.
 
template<typename TYPE>
constexpr bool is_null (TYPE const &value) noexcept
 Is value null?
 
template<typename... TYPE>
std::size_t size_buffer (TYPE const &...value) noexcept
 Estimate how much buffer space is needed to represent values as a string.
 
template<typename TYPE>
constexpr format param_format (TYPE const &)
 What's the preferred format for passing non-null parameters of this type?
 
template<typename TYPE>
zview generic_to_buf (char *begin, char *end, TYPE const &value)
 Implement string_traits<TYPE>::to_buf by calling into_buf.
 
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)
 End a code block started by "ignore-deprecated-pre.hxx".
 
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" }
 
std::string char const password []
 
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 T>
constexpr bool is_unquoted_safe< std::optional< T > > {is_unquoted_safe<T>}
 
template<typename... T>
constexpr bool is_unquoted_safe< std::variant< T... > >
 
template<>
constexpr bool is_unquoted_safe< std::nullptr_t > {true}
 
template<typename T, typename... Args>
constexpr bool is_unquoted_safe< std::unique_ptr< T, Args... > >
 
template<typename T>
constexpr bool is_unquoted_safe< std::shared_ptr< T > >
 
template<typename T>
constexpr bool is_sql_array< std::vector< T > > {true}
 
template<typename T, std::size_t N>
constexpr bool is_sql_array< std::array< T, N > > {true}
 
template<>
std::string_view const type_name< pqxx::internal::encoding_group > { "pqxx::internal::encoding_group" }
 
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.
 
template<typename TYPE>
constexpr bool is_sql_array {false}
 Does this type translate to an SQL array?
 
template<typename TYPE>
constexpr bool is_unquoted_safe {false}
 Can we use this type in arrays and composite types without quoting them?
 
template<typename T>
constexpr char array_separator {','}
 Element separator between SQL array elements of this type.
 
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) 2000-2024, 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) 2000-2024, 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) 2000-2024, 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) 2000-2024, 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) 2000-2024, 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) 2000-2024, 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.
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

◆ bytes

using pqxx::bytes
Initial value:
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.

◆ bytes_view

Initial value:
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.

◆ connection_base

using pqxx::connection_base = connection
Deprecated
Old base class for connection. They are now the same class.

◆ fieldstream

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

◆ read_transaction

Initial value:
Standard back-end transaction, templatised on isolation level.
Definition transaction.hxx:72

Read-only transaction.

◆ strip_t

template<typename TYPE>
using pqxx::strip_t = 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 = 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 = 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

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)

End a code block started by "ignore-deprecated-pre.hxx".

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)
inlinenodiscardnoexcept

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

Returns a conservative estimate.

◆ encrypt_password()

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

Encrypt password.

Deprecated
Use connection::encrypt_password instead.

◆ from_string() [1/4]

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() [2/4]

template<typename TYPE>
TYPE pqxx::from_string ( std::string_view text)
inlinenodiscard

Parse a value in postgres' text format as a TYPE.

If the form of the value found in the string does not match the expected type, e.g. if a decimal point is found when converting to an integer type, the conversion fails. Overflows (e.g. converting "9999999999" to a 16-bit C++ type) are also treated as errors. If in some cases this behaviour should be inappropriate, convert to something bigger such as long int first and then truncate the resulting value.

Only the simplest possible conversions are supported. Fancy features like hexadecimal or octal, spurious signs, or exponent notation won't work. Whitespace is not stripped away. Only the kinds of strings that come out of PostgreSQL and out of to_string() can be converted.

◆ from_string() [3/4]

template<>
std::string_view pqxx::from_string ( std::string_view text)
inlinenodiscard

"Convert" a std::string_view to a std::string_view.

Just returns its input.

Warning
Of course the result is only valid for as long as the original string remains valid! Never access the string referenced by the return value after the original has been destroyed.

◆ from_string() [4/4]

template<typename T>
void pqxx::from_string ( std::string_view text,
T & value )
inline

Attempt to convert postgres-generated string to given built-in object.

This is like the single-argument form of the function, except instead of returning the value, it sets value.

You may find this more convenient in that it infers the type you want from the argument you pass. But there are disadvantages: it requires an assignment operator, and it may be less efficient.

◆ 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.

◆ generic_to_buf()

template<typename TYPE>
zview pqxx::generic_to_buf ( char * begin,
char * end,
TYPE const & value )
inline

Implement string_traits<TYPE>::to_buf by calling into_buf.

When you specialise string_traits for a new type, most of the time its to_buf implementation has no special optimisation tricks and just writes its text into the buffer it receives from the caller, starting at the beginning.

In that common situation, you can implement to_buf as just a call to generic_to_buf. It will call into_buf and return the right result for to_buf.

◆ into_string()

template<typename TYPE>
void pqxx::into_string ( TYPE const & value,
std::string & out )
inline

Convert a value to a readable string that PostgreSQL will understand.

This variant of to_string can sometimes save a bit of time in loops, by re-using a std::string for multiple conversions.

◆ 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()

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;
Result set containing data returned by a query or command.
Definition result.hxx:92

◆ param_format()

template<typename TYPE>
format pqxx::param_format ( TYPE const & )
inlineconstexpr

What's the preferred format for passing non-null parameters of this type?

This affects how we pass parameters of TYPE when calling parameterised statements or prepared statements.

Generally we pass parameters in text format, but binary strings are the exception. We also pass nulls in binary format, so this function need not handle null values.

◆ 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
callbackTransaction code that can be called with no arguments.
attemptsMaximum 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 )
inlinenodiscard

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
sepseparator string (to be placed between items)
beginbeginning of items sequence
endend of items sequence
accessfunctor defining how to dereference sequence elements

◆ size_buffer()

template<typename... TYPE>
std::size_t pqxx::size_buffer ( TYPE const &... value)
inlinenodiscardnoexcept

Estimate how much buffer space is needed to represent values as a string.

The estimate may be a little pessimistic, if it saves time. It also includes room for a terminating zero after each value.

◆ 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_buf()

template<typename... TYPE>
std::vector< std::string_view > pqxx::to_buf ( char * here,
char const * end,
TYPE... value )
inlinenodiscard

Convert multiple values to strings inside a single buffer.

There must be enough room for all values, or this will throw conversion_overrun. You can obtain a conservative estimate of the buffer space required by calling size_buffer() on the values.

The std::string_view results may point into the buffer, so don't assume that they will remain valid after you destruct or move the buffer.

◆ to_string()

template<typename TYPE>
std::string pqxx::to_string ( TYPE const & value)
inline

Convert a value to a readable string that PostgreSQL will understand.

The conversion does no special formatting, and ignores any locale settings. The resulting string will be human-readable and in a format suitable for use in SQL queries. It won't have niceties such as "thousands separators" though.

Variable Documentation

◆ from_query

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

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

bool pqxx::has_generic_bytes_char_traits
inlineconstexpr

◆ is_sql_array

template<typename TYPE>
bool pqxx::is_sql_array {false}
inlineconstexpr

Does this type translate to an SQL array?

Specialisations may override this to be true for container types.

This may not always be a black-and-white choice. For instance, a std::string is a container, but normally it translates to an SQL string, not an SQL array.

◆ is_unquoted_safe

template<typename TYPE>
bool pqxx::is_unquoted_safe {false}
inlineconstexpr

Can we use this type in arrays and composite types without quoting them?

Define this as true only if values of TYPE can never contain any special characters that might need escaping or confuse the parsing of array or composite * types, such as commas, quotes, parentheses, braces, newlines, and so on.

When converting a value of such a type to a string in an array or a field in a composite type, we do not need to add quotes, nor escape any special characters.

This is just an optimisation, so it defaults to false to err on the side of slow correctness.

◆ is_unquoted_safe< std::shared_ptr< T > >

template<typename T>
bool pqxx::is_unquoted_safe< std::shared_ptr< T > >
inlineconstexpr
Initial value:
{
constexpr bool is_unquoted_safe
Can we use this type in arrays and composite types without quoting them?
Definition strconv.hxx:555

◆ is_unquoted_safe< std::unique_ptr< T, Args... > >

template<typename T, typename... Args>
bool pqxx::is_unquoted_safe< std::unique_ptr< T, Args... > >
inlineconstexpr
Initial value:

◆ is_unquoted_safe< std::variant< T... > >

template<typename... T>
bool pqxx::is_unquoted_safe< std::variant< T... > >
inlineconstexpr
Initial 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.