json/docs/mkdocs/docs/api/basic_json_view/index.md

nlohmann::basic_json_view

Defined in header <nlohmann/json_view.hpp>

template<typename BasicJsonType>
class basic_json_view;

A read-only handle to one value of a basic_json_document: two pointers (a pointer to the document and a pointer into its index), trivially copyable. A view is valid as long as

• the document is alive,
• the document has not been re-parsed with read() (or parse() into it) or shrunk with shrink_to_fit() since the view was taken, and
• if the document borrows its source text, that text is still alive.

Moving the document itself does not invalidate its views: the index is heap-allocated independently of the basic_json_document object.

basic_json_view provides the read-only part of the BasicJsonType interface: the type-inspection functions, and materialize() to build the BasicJsonType value of a subtree on demand. It does not (yet) provide element access, iteration, get<T>(), JSON Pointer support, dump(), or comparison.

Template parameters

BasicJsonType

a specialization of basic_json, matching the basic_json_document the view was taken from.

Specializations

• json_view - views of a json_document
• ordered_json_view - views of an ordered_json_document

Member types

• value_t - the JSON type enumeration, see basic_json::value_t
• string_t, number_integer_t, number_unsigned_t, number_float_t, json_pointer - the corresponding member types of BasicJsonType
• size_type - #!cpp std::size_t
• string_view_t - #!cpp std::string_view on C++17 and newer, a minimal internal substitute otherwise

Member functions

• (constructor)

Object inspection

• type - return the type of the value
• is_null - return whether the value is null
• is_boolean - return whether the value is a boolean
• is_number - return whether the value is a number
• is_number_integer - return whether the value is an integer number
• is_number_unsigned - return whether the value is an unsigned integer number
• is_number_float - return whether the value is a floating-point number
• is_string - return whether the value is a string
• is_array - return whether the value is an array
• is_object - return whether the value is an object
• is_binary - return whether the value is a binary array (always #!cpp false)
• is_primitive - return whether the type is primitive
• is_structured - return whether the type is structured
• is_discarded - return whether the view is invalid

Capacity

• size - return the number of elements
• empty - return whether the value has no elements

Conversion

• materialize - build the BasicJsonType value of this subtree

Source access

• source_offset - byte offset of this value in the document's source text

Version history

• Added in version 3.13.0.