Reading column values

Reads values from columns of the current rowset. More...

Functions
template<class T >
void	nanodbc::result::get_ref (short column, T &result) const
	Gets data from the given column of the current rowset.
template<class T >
void	nanodbc::result::get_ref (short column, T const &fallback, T &result) const
	Gets data from the given column of the current rowset.
template<class T >
void	nanodbc::result::get_ref (string const &column_name, T &result) const
	Gets data from the given column by name of the current rowset.
template<class T >
void	nanodbc::result::get_ref (string const &column_name, T const &fallback, T &result) const
	Gets data from the given column by name of the current rowset.
template<class T >
T	nanodbc::result::get (short column) const
	Gets data from the given column of the current rowset.
template<class T >
T	nanodbc::result::get (short column, T const &fallback) const
	Gets data from the given column of the current rowset.
template<class T >
T	nanodbc::result::get_as (short column) const
	Reads a column as whatever it holds, into a type able to hold any of them.
template<class T >
T	nanodbc::result::get_as (string const &column_name) const
	Reads a column by name as whatever it holds.
template<class T >
T	nanodbc::result::get (string const &column_name) const
	Gets data from the given column by name of the current rowset.
template<class T >
T	nanodbc::result::get (string const &column_name, T const &fallback) const
	Gets data from the given column by name of the current rowset.

Detailed Description

Reads values from columns of the current rowset.

Attention

When nanodbc is compiled as a library, get() and get_ref() are only available for the types they are explicitly instantiated for in nanodbc.cpp. Using any other type compiles, because the declaration is visible here, but fails to link. The supported types are: bool, signed char, unsigned char, short, unsigned short, int, unsigned int, long int, unsigned long int, long long int, unsigned long long int, float, double, std::string, wide_string, std::string::value_type, wide_string::value_type, date, time, timestamp, timestampoffset and std::vector<std::uint8_t> for binary data. Each is also available wrapped in std::optional, which is how a null column is read without an exception, and _variant_t on MSVC.

Function Documentation

get_ref() [1/4]

template<class T >

void nanodbc::result::get_ref	(	short	column,
		T &	result
	)		const

Gets data from the given column of the current rowset.

Columns are numbered from left to right and 0-indexed.

Parameters

column	position.
result	The column's value will be written to this parameter.

Exceptions

database_error
index_range_error
type_incompatible_error
null_access_error

get_ref() [2/4]

template<class T >

void nanodbc::result::get_ref	(	short	column,
		T const &	fallback,
		T &	result
	)		const

Gets data from the given column of the current rowset.

If the data is null, fallback is returned instead.

Columns are numbered from left to right and 0-indexed.

Parameters

column	position.
fallback	if value is null, return fallback instead.
result	The column's value will be written to this parameter.

Exceptions

database_error
index_range_error
type_incompatible_error

get_ref() [3/4]

template<class T >

void nanodbc::result::get_ref	(	string const &	column_name,
		T &	result
	)		const

Gets data from the given column by name of the current rowset.

Parameters

column_name	column's name.
result	The column's value will be written to this parameter.

Exceptions

database_error
index_range_error
type_incompatible_error
null_access_error

get_ref() [4/4]

template<class T >

void nanodbc::result::get_ref	(	string const &	column_name,
		T const &	fallback,
		T &	result
	)		const

Gets data from the given column by name of the current rowset.

If the data is null, fallback is returned instead.

Parameters

column_name	column's name.
fallback	if value is null, return fallback instead.
result	The column's value will be written to this parameter.

Exceptions

database_error
index_range_error
type_incompatible_error

get() [1/4]

template<class T >

T nanodbc::result::get

(

short

column

)

const

Gets data from the given column of the current rowset.

Columns are numbered from left to right and 0-indexed.

Parameters

column

position.

Exceptions

database_error
index_range_error
type_incompatible_error
null_access_error

T may be std::any, which is filled according to what the column says it holds rather than what the caller asks for. A null column gives an any holding nothing.

See also

column_datatype(), get_as()

get() [2/4]

template<class T >

T nanodbc::result::get	(	short	column,
		T const &	fallback
	)		const

Gets data from the given column of the current rowset.

If the data is null, fallback is returned instead.

Columns are numbered from left to right and 0-indexed.

Parameters

column	position.
fallback	if value is null, return fallback instead.

Exceptions

database_error
index_range_error
type_incompatible_error

get_as() [1/2]

template<class T >

T nanodbc::result::get_as

(

short

column

)

const

Reads a column as whatever it holds, into a type able to hold any of them.

Where get() reads a column as the type the caller names, converting where it can, this reads it as the type the column says it is and hands back a T holding that. T may be std::any, or a std::variant naming the alternatives to choose between.

A null column gives a T built from nothing: an any holding nothing, or a variant on its first alternative, which is what std::monostate is for.

using v_t = std::variant<std::monostate, nanodbc::string, int>;
auto v = results.get_as<v_t>(0);

Parameters

column

position.

Exceptions

database_error
index_range_error
type_incompatible_error	if the column holds something T cannot.

See also

get(), column_datatype()

get_as() [2/2]

template<class T >

T nanodbc::result::get_as

(

string const &

column_name

)

const

Reads a column by name as whatever it holds.

See also

get_as(short)

get() [3/4]

template<class T >

T nanodbc::result::get

(

string const &

column_name

)

const

Gets data from the given column by name of the current rowset.

Parameters

column_name

column's name.

Exceptions

database_error
index_range_error
type_incompatible_error
null_access_error

get() [4/4]

template<class T >

T nanodbc::result::get	(	string const &	column_name,
		T const &	fallback
	)		const

Gets data from the given column by name of the current rowset.

If the data is null, fallback is returned instead.

Parameters

column_name	column's name.
fallback	if value is null, return fallback instead.

Exceptions

database_error
index_range_error
type_incompatible_error