Classes
struct	pqxx::nullness< TYPE, ENABLE >
	Traits describing a type's "null value," if any. More...

struct	pqxx::no_null< TYPE >
	Nullness traits describing a type which does not have a null value. More...

struct	pqxx::string_traits< TYPE >
	Traits class for use in string conversions. More...

struct	pqxx::nullness< ENUM, std::enable_if_t< std::is_enum_v< ENUM > > >
	Nullness: Enums do not have an inherent null value. More...

struct	pqxx::internal::enum_traits< ENUM >
	Helper class for defining enum conversions. More...

Typedefs
using	pqxx::internal::enum_traits< ENUM >::impl_type = std::underlying_type_t< ENUM >

using	pqxx::internal::enum_traits< ENUM >::impl_traits = string_traits< impl_type >

Functions
static bool	pqxx::nullness< TYPE, ENABLE >::is_null (TYPE const &value)
	Is `value` a null? More...

static TYPE	pqxx::nullness< TYPE, ENABLE >::null ()
	Return a null value. More...

static constexpr bool	pqxx::no_null< TYPE >::is_null (TYPE const &) noexcept
	Does a given value correspond to an SQL null value? More...

static zview	pqxx::string_traits< TYPE >::to_buf (char begin, char end, TYPE const &value)
	Return a `string_view` representing value, plus terminating zero. More...

static char *	pqxx::string_traits< TYPE >::into_buf (char begin, char end, TYPE const &value)
	Write value's string representation into buffer at `begin`. More...

static TYPE	pqxx::string_traits< TYPE >::from_string (std::string_view text)
	Parse a string representation of a `TYPE` value. More...

static std::size_t	pqxx::string_traits< TYPE >::size_buffer (TYPE const &value) noexcept
	Estimate how much buffer space is needed to represent value. More...

static constexpr zview	pqxx::internal::enum_traits< ENUM >::to_buf (char begin, char end, ENUM const &value)

static constexpr char *	pqxx::internal::enum_traits< ENUM >::into_buf (char begin, char end, ENUM const &value)

static ENUM	pqxx::internal::enum_traits< ENUM >::from_string (std::string_view text)

static std::size_t	pqxx::internal::enum_traits< ENUM >::size_buffer (ENUM const &value) noexcept

template<typename TYPE >
TYPE	pqxx::from_string (std::string_view text)
	Parse a value in postgres' text format as a TYPE. More...

template<>
std::string_view	pqxx::from_string (std::string_view text)
	"Convert" a std::string_view to a std::string_view. More...

template<typename T >
void	pqxx::from_string (std::string_view text, T &value)
	Attempt to convert postgres-generated string to given built-in object. More...

template<typename TYPE >
std::string	pqxx::to_string (TYPE const &value)
	Convert a value to a readable string that PostgreSQL will understand. More...

template<typename... TYPE>
std::vector< std::string_view >	pqxx::to_buf (char here, char const end, TYPE... value)
	Convert multiple values to strings inside a single buffer. More...

template<typename TYPE >
void	pqxx::into_string (TYPE const &value, std::string &out)
	Convert a value to a readable string that PostgreSQL will understand. More...

template<typename TYPE >
bool	pqxx::is_null (TYPE const &value) noexcept
	Is `value` null? More...

template<typename... TYPE>
std::size_t	pqxx::size_buffer (TYPE const &...value) noexcept
	Estimate how much buffer space is needed to represent values as a string. More...

template<typename TYPE >
constexpr format	pqxx::param_format (TYPE const &)
	What's the preferred format for passing non-null parameters of this type? More...

Variables
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. More...

static bool	pqxx::nullness< TYPE, ENABLE >::has_null
	Does this type have a null value? More...

static bool	pqxx::nullness< TYPE, ENABLE >::always_null
	Is this type always null? More...

static constexpr bool	pqxx::no_null< TYPE >::has_null = false
	Does `TYPE` have a "built-in null value"? More...

static constexpr bool	pqxx::no_null< TYPE >::always_null = false
	Are all values of this type null? More...

template<typename TYPE >
constexpr bool	pqxx::is_sql_array {false}
	Does this type translate to an SQL array? More...

template<typename TYPE >
constexpr bool	pqxx::is_unquoted_safe {false}
	Can we use this type in arrays and composite types without quoting them? More...

template<typename T >
constexpr char	pqxx::array_separator {','}
	Element separator between SQL array elements of this type. More...

Detailed Description

The PostgreSQL server accepts and represents data in string form. It has its own formats for various data types. The string conversions define how various C++ types translate to and from their respective PostgreSQL text representations.

Each conversion is defined by a specialisations of string_traits. It gets complicated if you want top performance, but until you do, all you really need to care about when converting values between C++ in-memory representations such as int and the postgres string representations is the pqxx::to_string and pqxx::from_string functions.

If you need to convert a type which is not supported out of the box, you'll need to define your own specialisations for these templates, similar to the ones defined here and in pqxx/conversions.hxx. Any conversion code which "sees" your specialisation will now support your conversion. In particular, you'll be able to read result fields into a variable of the new type.

There is a macro to help you define conversions for individual enumeration types. The conversion will represent enumeration values as numeric strings.

Typedef Documentation

◆ impl_traits

template<typename ENUM >

using pqxx::internal::enum_traits< ENUM >::impl_traits = string_traits<impl_type>

◆ impl_type

template<typename ENUM >

using pqxx::internal::enum_traits< ENUM >::impl_type = std::underlying_type_t<ENUM>

Function Documentation

◆ from_string() [1/5]

template<typename TYPE>

bool pqxx::string_traits< TYPE >::from_string ( std::string_view text )

static

Parse a string representation of a TYPE value.

Throws conversion_error if value does not meet the expected format for a value of this type.

Referenced by pqxx::from_string().

◆ from_string() [2/5]

template<typename ENUM >

static ENUM pqxx::internal::enum_traits< ENUM >::from_string ( std::string_view text )

static

References pqxx::from_string().

◆ from_string() [3/5]

template<typename TYPE >

TYPE pqxx::from_string ( std::string_view text )

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.

References pqxx::string_traits< TYPE >::from_string().

Referenced by pqxx::internal::to_string_float().

◆ from_string() [4/5]

template<>

std::string_view pqxx::from_string ( std::string_view text )

"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() [5/5]

template<typename T >

void pqxx::from_string	(	std::string_view	text,
		T &	value
	)

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.

References pqxx::to_string().

Referenced by pqxx::internal::enum_traits< ENUM >::from_string().

◆ into_buf() [1/2]

template<typename TYPE>

static char* pqxx::string_traits< TYPE >::into_buf	(	char *	begin,
		char *	end,
		TYPE const &	value
	)

static

Write value's string representation into buffer at begin.

Assumes that value is non-null.

Writes value's string representation into the buffer, starting exactly at begin, and ensuring a trailing zero. Returns the address just beyond the trailing zero, so the caller could use it as the begin for another call to into_buf writing a next value.

◆ into_buf() [2/2]

template<typename ENUM >

static constexpr char* pqxx::internal::enum_traits< ENUM >::into_buf	(	char *	begin,
		char *	end,
		ENUM const &	value
	)

static

◆ into_string()

template<typename TYPE >

void pqxx::into_string	(	TYPE const &	value,
		std::string &	out
	)

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.

Referenced by pqxx::to_buf().

◆ is_null() [1/3]

template<typename TYPE, typename ENABLE = void>

static bool pqxx::nullness< TYPE, ENABLE >::is_null ( TYPE const & value )

static

Is value a null?

◆ is_null() [2/3]

template<typename TYPE>

static constexpr bool pqxx::no_null< TYPE >::is_null ( TYPE const & )

staticnoexcept

Does a given value correspond to an SQL null value?

Most C++ types, such as int or std::string, have no inherent null value. But some types such as C-style string pointers do have a natural equivalent to an SQL null.

◆ is_null() [3/3]

template<typename TYPE >

bool pqxx::is_null ( TYPE const & value )

noexcept

Is value null?

Referenced by pqxx::params::append(), pqxx::field::as(), pqxx::field::composite_to(), pqxx::field::as< std::string_view >(), pqxx::field::to< std::string >(), pqxx::field::to< std::string_view >(), pqxx::field::num(), pqxx::connection::quote(), pqxx::field::to(), and pqxx::stream_to::write_values().

◆ null()

template<typename TYPE, typename ENABLE = void>

static TYPE pqxx::nullness< TYPE, ENABLE >::null ( )

static

Return a null value.

Don't use this in generic code to compare a value and see whether it is null. Some types may have multiple null values which do not compare as equal, or may define a null value which is not equal to anything including itself, like in SQL.

Referenced by pqxx::field::as(), and pqxx::from_string().

◆ param_format()

template<typename TYPE >

constexpr format pqxx::param_format ( TYPE const & )

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.

References pqxx::text.

Referenced by pqxx::params::make_c_params().

◆ size_buffer() [1/3]

template<typename TYPE>

static std::size_t pqxx::string_traits< TYPE >::size_buffer ( TYPE const & value )

staticnoexcept

Estimate how much buffer space is needed to represent value.

The estimate may be a little pessimistic, if it saves time.

The estimate includes the terminating zero.

◆ size_buffer() [2/3]

template<typename ENUM >

static std::size_t pqxx::internal::enum_traits< ENUM >::size_buffer ( ENUM const & value )

staticnoexcept

References pqxx::size_buffer().

◆ size_buffer() [3/3]

template<typename... TYPE>

std::size_t pqxx::size_buffer ( TYPE const &... value )

noexcept

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.

Referenced by pqxx::string_traits< binarystring >::into_buf(), pqxx::separated_list(), pqxx::internal::enum_traits< ENUM >::size_buffer(), pqxx::internal::to_string_float(), and pqxx::stream_to::write_values().

◆ to_buf() [1/3]

template<typename TYPE>

static zview pqxx::string_traits< TYPE >::to_buf	(	char *	begin,
		char *	end,
		TYPE const &	value
	)

static

Return a string_view representing value, plus terminating zero.

Produces a string_view containing the PostgreSQL string representation for value.

Uses the space from begin to end as a buffer, if needed. The returned string may lie somewhere in that buffer, or it may be a compile-time constant, or it may be null if value was a null value. Even if the string is stored in the buffer, its begin() may or may not be the same as begin.

The string_view is guaranteed to be valid as long as the buffer from begin to end remains accessible and unmodified.

Exceptions

pqxx::conversion_overrun if the provided buffer space may not be enough. For maximum performance, this is a conservative estimate. It may complain about a buffer which is actually large enough for your value, if an exact check gets too expensive.

◆ to_buf() [2/3]

template<typename ENUM >

static constexpr zview pqxx::internal::enum_traits< ENUM >::to_buf	(	char *	begin,
		char *	end,
		ENUM const &	value
	)

static

References pqxx::to_buf().

◆ to_buf() [3/3]

template<typename... TYPE>

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

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.

References pqxx::into_string().

Referenced by pqxx::blob::read(), pqxx::internal::state_buffer_overrun(), pqxx::internal::enum_traits< ENUM >::to_buf(), pqxx::internal::to_string_float(), and pqxx::stream_to::write_values().

◆ to_string()

template<typename TYPE >

std::string pqxx::to_string ( TYPE const & value )

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.

Referenced by pqxx::largeobject_streambuf< CHAR, TRAITS >::overflow().

Variable Documentation

◆ always_null [1/2]

template<typename TYPE, typename ENABLE = void>

bool pqxx::nullness< TYPE, ENABLE >::always_null

static

Is this type always null?

◆ always_null [2/2]

template<typename TYPE>

constexpr bool pqxx::no_null< TYPE >::always_null = false

static

Are all values of this type null?

There are a few special C++ types which are always null - mainly std::nullptr_t.

◆ array_separator

template<typename T >

constexpr char pqxx::array_separator {','}

Element separator between SQL array elements of this type.

◆ has_null [1/2]

template<typename TYPE, typename ENABLE = void>

bool pqxx::nullness< TYPE, ENABLE >::has_null

static

Does this type have a null value?

◆ has_null [2/2]

template<typename TYPE>

constexpr bool pqxx::no_null< TYPE >::has_null = false

static

Does TYPE have a "built-in null value"?

For example, a pointer can equal nullptr, which makes a very natural representation of an SQL null value. For such types, the code sometimes needs to make special allowances.

for most types, such as int or std::string, there is no built-in null. If you want to represent an SQL null value for such a type, you would have to wrap it in something that does have a null value. For example, you could use std::optional<int> for "either an @c int or a null value."

◆ is_sql_array

template<typename TYPE >

constexpr bool pqxx::is_sql_array {false}

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 >

constexpr bool pqxx::is_unquoted_safe {false}

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.

◆ 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.

Classes

Typedefs

Functions

Variables

Detailed Description

Typedef Documentation

◆ impl_traits

◆ impl_type

Function Documentation

◆ from_string() [1/5]

◆ from_string() [2/5]

◆ from_string() [3/5]

◆ from_string() [4/5]

◆ from_string() [5/5]

◆ into_buf() [1/2]

◆ into_buf() [2/2]

◆ into_string()

◆ is_null() [1/3]

◆ is_null() [2/3]

◆ is_null() [3/3]

◆ null()

◆ param_format()

◆ size_buffer() [1/3]

◆ size_buffer() [2/3]

◆ size_buffer() [3/3]

◆ to_buf() [1/3]

◆ to_buf() [2/3]

◆ to_buf() [3/3]

◆ to_string()

Variable Documentation

◆ always_null [1/2]

◆ always_null [2/2]

◆ array_separator

◆ has_null [1/2]

◆ has_null [2/2]

◆ is_sql_array

◆ is_unquoted_safe

◆ type_name