pqxx::field Class Reference

Reference to a field in a result set. More...

#include <field.hxx>

Inheritance diagram for pqxx::field:

Collaboration diagram for pqxx::field:

Public Types
typedef size_t	size_type

Public Member Functions
	field (const tuple &T, tuple_size_type C) throw ()
	Constructor. More...
template<>
bool	to (const char *&Obj) const
	Specialization: to(const char *&). More...
Comparison
bool	operator== (const field &) const
	Byte-by-byte comparison of two fields (all nulls are considered equal) More...
bool	operator!= (const field &rhs) const
	Byte-by-byte comparison (all nulls are considered equal) More...
Column information
const char *	name () const
	Column name. More...
oid	type () const
	Column type. More...
oid	table () const
	What table did this column come from? More...
tuple_size_type	num () const
tuple_size_type	table_column () const
	What column number in its originating table did this column come from? More...
Content access
const char *	c_str () const
	Read as plain C string. More...
template<typename T >
bool	to (T &Obj) const
	Read value into Obj; or leave Obj untouched and return false if null. More...
template<typename T >
bool	operator>> (T &Obj) const
	Read value into Obj; or leave Obj untouched and return false if null. More...
template<typename T >
bool	to (T &Obj, const T &Default) const
	Read value into Obj; or use Default & return false if null. More...
template<typename T >
T	as (const T &Default) const
	Return value as object of given type, or Default if null. More...
template<typename T >
T	as () const
	Return value as object of given type, or throw exception if null. More...
bool	is_null () const throw ()
size_type	size () const throw ()

Protected Member Functions
tuple_size_type	col () const throw ()
const result *	home () const throw ()
size_t	idx () const throw ()

Protected Attributes
tuple_size_type	m_col

Private Attributes
const result *	m_home
size_t	m_row

Detailed Description

Reference to a field in a result set.

A field represents one entry in a tuple. It represents an actual value in the result set, and can be converted to various types.

Member Typedef Documentation

typedef size_t pqxx::field::size_type

Constructor & Destructor Documentation

pqxx::field::field	(	const tuple &	T,
		tuple_size_type	C
	)		throw ()

Constructor.

Create field as reference to a field in a result set.

Parameters

T	Tuple that this field is part of.
C	Column number of this field.

Member Function Documentation

template<typename T >

T pqxx::field::as ( const T &  Default ) const

inline

Return value as object of given type, or Default if null.

Note that unless the function is instantiated with an explicit template argument, the Default value's type also determines the result type.

template<typename T >

T pqxx::field::as ( ) const

inline

Return value as object of given type, or throw exception if null.

const char* pqxx::field::c_str

(

)

const

Read as plain C string.

Since the field's data is stored internally in the form of a zero-terminated C string, this is the fastest way to read it. Use the to() or as() functions to convert the string to other types such as int, or to C++ strings.

Referenced by pqxx::from_string(), pqxx::field_streambuf< CHAR, TRAITS >::initialize(), pqxx::operator<<(), and pqxx::to_string().

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tuple_size_type pqxx::field::col ( ) const throw ()

inlineprotected

const result* pqxx::field::home ( ) const throw ()

inlineprotected

size_t pqxx::field::idx ( ) const throw ()

inlineprotected

bool pqxx::field::is_null

(

)

const throw ()

const char* pqxx::field::name

(

)

const

Column name.

tuple_size_type pqxx::field::num ( ) const

inline

Referenced by pqxx::const_tuple_iterator::operator-().

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bool pqxx::field::operator!= ( const field &  rhs ) const

inline

Byte-by-byte comparison (all nulls are considered equal)

Warning

See operator==() for important information about this operator

bool pqxx::field::operator==

(

const field &

)

const

Byte-by-byte comparison of two fields (all nulls are considered equal)

Warning

null handling is still open to discussion and change!

Handling of null values differs from that in SQL where a comparison involving a null value yields null, so nulls are never considered equal to one another or even to themselves.

Null handling also probably differs from the closest equivalent in C++, which is the NaN (Not-a-Number) value, a singularity comparable to SQL's null. This is because the builtin == operator demands that a == a.

The usefulness of this operator is questionable. No interpretation whatsoever is imposed on the data; 0 and 0.0 are considered different, as are null vs. the empty string, or even different (but possibly equivalent and equally valid) encodings of the same Unicode character etc.

template<typename T >

bool pqxx::field::operator>> ( T &  Obj ) const

inline

Read value into Obj; or leave Obj untouched and return false if null.

size_type pqxx::field::size

(

)

const throw ()

Referenced by pqxx::from_string(), pqxx::field_streambuf< CHAR, TRAITS >::initialize(), pqxx::operator<<(), and pqxx::to_string().

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oid pqxx::field::table

(

)

const

What table did this column come from?

tuple_size_type pqxx::field::table_column

(

)

const

What column number in its originating table did this column come from?

template<typename T >

bool pqxx::field::to ( T &  Obj ) const

inline

Read value into Obj; or leave Obj untouched and return false if null.

References pqxx::from_string().

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template<typename T >

bool pqxx::field::to ( T &  Obj, const T &  Default  ) const

inline

Read value into Obj; or use Default & return false if null.

template<>

bool pqxx::field::to ( const char *&  Obj ) const

inline

Specialization: to(const char *&).

The buffer has the same lifetime as the data in this result (i.e. of this result object, or the last remaining one copied from it etc.), so take care not to use it after the last result object referring to this query result is destroyed.

oid pqxx::field::type

(

)

const

Column type.

Member Data Documentation

tuple_size_type pqxx::field::m_col

protected

const result* pqxx::field::m_home

private

size_t pqxx::field::m_row

private

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The documentation for this class was generated from the following file:

• /usr/include/pqxx/field.hxx