array

A dynamically sized array of JSON values.

Synopsis

Defined in header <boost/json/array.hpp>

class array;

Types

Name	Description
allocator_type	Associated Allocator
const_iterator	A random access const iterator to an element.
const_pointer	A const pointer to an element.
const_reference	A const reference to an element.
const_reverse_iterator	A reverse random access const iterator to an element.
difference_type	The type used to represent signed integers.
iterator	A random access iterator to an element.
pointer	A pointer to an element.
reference	A reference to an element.
reverse_iterator	A reverse random access iterator to an element.
size_type	The type used to represent unsigned integers.
value_type	The type of each element.

Member Functions

Name	Description
array [constructor]	Constructor. — Copy constructor. — Pilfer constructor. — Move constructor.
at	Access an element, with bounds checking.
back	Access the last element.
begin	Return an iterator to the first element. — Return a const iterator to the first element.
capacity	Return the number of elements that can be held in currently allocated memory.
cbegin	Return a const iterator to the first element.
cend	Return a const iterator to the element following the last element.
clear	Clear the contents.
crbegin	Return a const reverse iterator to the first element of the reversed container.
crend	Return a const reverse iterator to the element following the last element of the reversed container.
data	Access the underlying array directly.
emplace	Insert a constructed element in-place.
emplace_back	Append a constructed element in-place.
empty	Check if the array has no elements.
end	Return an iterator to the element following the last element. — Return a const iterator to the element following the last element.
erase	Erase elements from the container.
front	Access the first element.
get_allocator	Return the associated allocator.
if_contains	Return a pointer to an element, or nullptr if the index is invalid.
insert	Insert elements before the specified location.
operator=	Copy assignment. — Move assignment. — Assignment.
operator[]	Access an element.
pop_back	Remove the last element.
push_back	Add an element to the end.
rbegin	Return a reverse iterator to the first element of the reversed container. — Return a const reverse iterator to the first element of the reversed container.
rend	Return a reverse iterator to the element following the last element of the reversed container. — Return a const reverse iterator to the element following the last element of the reversed container.
reserve	Increase the capacity to at least a certain amount.
resize	Change the number of elements stored.
shrink_to_fit	Request the removal of unused capacity.
size	Return the number of elements in the array.
storage	Return the associated memory resource.
swap	Swap the contents.
try_at	Access an element, with bounds checking.
~array [destructor]	Destructor.

Static Member Functions

Name	Description
max_size	Return the maximum number of elements any array can hold.

Friends

Name	Description
operator!=	Return `true` if two arrays are not equal.
operator<<	Serialize `array` to an output stream.
operator==	Return `true` if two arrays are equal.
swap	Exchange the given values.

Description

This is the type used to represent a JSON array as a modifiable container. The interface and performance characteristics are modeled after std::vector<value>.

Elements are stored contiguously, which means that they can be accessed not only through iterators, but also using offsets to regular pointers to elements. A pointer to an element of an array may be passed to any function that expects a pointer to value.

The storage of the array is handled automatically, being expanded and contracted as needed. Arrays usually occupy more space than array language constructs, because more memory is allocated to handle future growth. This way an array does not need to reallocate each time an element is inserted, but only when the additional memory is used up. The total amount of allocated memory can be queried using the capacity function. Extra memory can be relinquished by calling shrink_to_fit.

Reallocations are usually costly operations in terms of performance. The reserve function can be used to eliminate reallocations if the number of elements is known beforehand.

The complexity (efficiency) of common operations on arrays is as follows:

Random access - constant O(1).
Insertion or removal of elements at the end - amortized constant O(1).
Insertion or removal of elements - linear in the distance to the end of the array O(n).

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