pqxx::result::field Class Reference

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

#include <result.hxx>

Inheritance diagram for pqxx::result::field:

Inheritance graph
[legend]
List of all members.

Public Types

typedef size_t size_type

Public Member Functions

 field (const tuple &T, tuple::size_type C) throw ()
 Constructor.
template<>
bool to (const char *&Obj) const
 Specialization: to(const char *&).
Comparison
bool operator== (const field &) const
 Byte-by-byte comparison of two fields (all nulls are considered equal).
bool operator!= (const field &rhs) const
 Byte-by-byte comparison (all nulls are considered equal).
Column information
const char * name () const
 Column name.
oid type () const
 Column type.
oid table () const
 What table did this column come from? Requires PostgreSQL 7.4 C API.
tuple::size_type num () const
tuple::size_type table_column () const
 What column number in its originating table did this column come from?
Content access
const char * c_str () const
 Read as plain C string.
template<typename T>
bool to (T &Obj) const
 Read value into Obj; or leave Obj untouched and return false if null.
template<typename T>
bool operator>> (T &Obj) const
 Read value into Obj; or leave Obj untouched and return false if null.
template<typename T>
bool to (T &Obj, const T &Default) const
 Read value into Obj; or use Default & return false if null.
template<typename T>
as (const T &Default) const
 Return value as object of given type, or Default if null.
template<typename T>
as () const
 Return value as object of given type, or throw exception if null.
bool is_null () const
size_type size () const throw ()

Protected Member Functions

tuple::size_type col () const throw ()

Protected Attributes

tuple m_tup
tuple::size_type m_col

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::result::field::size_type

Reimplemented in pqxx::result::const_fielditerator.


Constructor & Destructor Documentation

pqxx::result::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

bool pqxx::result::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.

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

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

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

const char* pqxx::result::field::name (  )  const

Column name.

oid pqxx::result::field::type (  )  const

Column type.

oid pqxx::result::field::table (  )  const

What table did this column come from? Requires PostgreSQL 7.4 C API.

Only defined if the libpqxx library was compiled against a libpq version that supports the PQftable function.

If you get a link error saying this function is undefined, that must be because libpqxx was compiled against an older version of libpq. The PQftable function first became available in PostgreSQL 7.4.

tuple::size_type pqxx::result::field::num (  )  const

tuple::size_type pqxx::result::field::table_column (  )  const

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

const char* pqxx::result::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.

template<typename T>
bool pqxx::result::field::to ( T &  Obj  )  const

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

template<typename T>
bool pqxx::result::field::operator>> ( T &  Obj  )  const

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

template<typename T>
bool pqxx::result::field::to ( T &  Obj,
const T &  Default 
) const

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

template<typename T>
T pqxx::result::field::as ( const T &  Default  )  const

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::result::field::as (  )  const

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

bool pqxx::result::field::is_null (  )  const

size_type pqxx::result::field::size (  )  const throw ()

tuple::size_type pqxx::result::field::col (  )  const throw () [protected]

template<>
bool pqxx::result::field::to ( const char *&  Obj  )  const

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.


Member Data Documentation

tuple pqxx::result::field::m_tup [protected]

tuple::size_type pqxx::result::field::m_col [protected]


The documentation for this class was generated from the following files:
Generated on Thu Feb 1 17:12:37 2007 for libpqxx by  doxygen 1.5.1