field_view

Non-owning variant-like class that can represent of any of the allowed database types.

Synopsis

Defined in header <boost/mysql/field_view.hpp>

class field_view;

Member Functions

Name	Description
as_blob	Retrieves the underlying value as a blob or throws an exception.
as_date	Retrieves the underlying value as a `date` or throws an exception.
as_datetime	Retrieves the underlying value as a `datetime` or throws an exception.
as_double	Retrieves the underlying value as a `double` or throws an exception.
as_float	Retrieves the underlying value as a `float` or throws an exception.
as_int64	Retrieves the underlying value as an `int64` or throws an exception.
as_string	Retrieves the underlying value as a string or throws an exception.
as_time	Retrieves the underlying value as a `time` or throws an exception.
as_uint64	Retrieves the underlying value as an `uint64` or throws an exception.
field_view [constructor]	Constructs a `field_view` holding NULL. — Constructs a `field_view` holding an `int64`. — Constructs a `field_view` holding a `uint64`. — Constructors from character types would incorrectly construct a `field_view` holding an integer, so they are not allowed. — Constructs a `field_view` holding a string. — Constructs a `field_view` holding a blob. — Constructs a `field_view` holding a `float`. — Constructs a `field_view` holding a `double`. — Constructs a `field_view` holding a `date`. — Constructs a `field_view` holding a `datetime`. — Constructs a `field_view` holding a `time`.
get_blob	Retrieves the underlying value as a blob (unchecked access).
get_date	Retrieves the underlying value as a `date` (unchecked access).
get_datetime	Retrieves the underlying value as a `datetime` (unchecked access).
get_double	Retrieves the underlying value as a `double` (unchecked access).
get_float	Retrieves the underlying value as a `float` (unchecked access).
get_int64	Retrieves the underlying value as an `int64` (unchecked access).
get_string	Retrieves the underlying value as a string (unchecked access).
get_time	Retrieves the underlying value as a `time` (unchecked access).
get_uint64	Retrieves the underlying value as an `uint64` (unchecked access).
is_blob	Returns whether this `field_view` points to a binary blob.
is_date	Returns whether this `field_view` points to a `date` value.
is_datetime	Returns whether this `field_view` points to a `datetime` value.
is_double	Returns whether this `field_view` points to a `double` value.
is_float	Returns whether this `field_view` points to a `float` value.
is_int64	Returns whether this `field_view` points to a `int64` value.
is_null	Returns whether this `field_view` points to a `NULL` value.
is_string	Returns whether this `field_view` points to a string value.
is_time	Returns whether this `field_view` points to a `time` value.
is_uint64	Returns whether this `field_view` points to a `uint64` value.
kind	Returns the type of the value this `field_view` is pointing to.
operator!=	Tests for inequality.
operator==	Tests for equality.

Related Non-member Functions

Name	Description
operator<<	Streams a `field_view`.

This is a variant-like class, similar to field, but semi-owning and read-only. Values of this type are usually created by the library, not directly by the user. It's cheap to construct and copy, and it's the main library interface when reading values from MySQL.

Like a variant, at any point, a field_view always points to a value of certain type. You can query the type using field_view::kind and the is_xxx functions like field_view::is_int64. Use as_xxx and get_xxx for checked and unchecked value access, respectively. As opposed to field, these functions return values instead of references.

Object lifetimes

Depending on how it was constructed, field_view can have value or reference semantics:

If it was created by the library, the field_view will have an associated row, rows or results object holding memory to which the field_view points. It will be valid as long as the memory allocated by that object is valid.
If it was created from a field (by calling operator field_view), the field_view acts as a reference to that field object, and will be valid as long as the field is.
If it was created from a scalar (null, integral, floating point, date, datetime or time), the field_view has value semnatics and will always be valid.
If it was created from a string or blob type, the field_view acts as a string_view or blob_view, and will be valid as long as the original string/blob is.

Calling any member function on a field_view that has been invalidated results in undefined behavior.

Convenience header <boost/mysql.hpp>