Type 5 – Maps

CBOR maps are the plain old associative maps similar JSON objects or Python dictionaries.

Definite maps have a fixed size which is stored in the header, whereas indefinite maps do not and are terminated by a special “break” byte instead.

Map are explicitly created or decoded as definite or indefinite and will be encoded using the corresponding wire representation, regardless of whether the actual size is known at the time of encoding.

Note

Indefinite maps can be conveniently used with streaming decoding and encoding. Keys and values can simply be output one by one, alternating keys and values.

Warning

Any CBOR data item is a legal map key (not just strings).

Corresponding cbor_type

CBOR_TYPE_MAP

Number of allocations (definite)

Two plus any manipulations with the data

Number of allocations (indefinite)

Two plus logarithmically many reallocations relative to additions

Storage requirements (definite)

sizeof(cbor_pair) * size + sizeof(cbor_item_t)

Storage requirements (indefinite)

<= sizeof(cbor_item_t) + sizeof(cbor_pair) * size * BUFFER_GROWTH

Examples

0xbf        Start indefinite map (represents {1: 2})
    0x01        Unsigned integer 1 (key)
    0x02        Unsigned integer 2 (value)
    0xff        "Break" control token
0xa0        Map of size 0

Getting metadata

size_t cbor_map_size(const cbor_item_t *item)

Get the number of pairs.

param item[borrow]

A map

return

The number of pairs

size_t cbor_map_allocated(const cbor_item_t *item)

Get the size of the allocated storage.

param item[borrow]

A map

return

Allocated storage size (as the number of cbor_pair items)

bool cbor_map_is_definite(const cbor_item_t *item)

Is this map definite?

param item[borrow]

A map

return

Is this map definite?

bool cbor_map_is_indefinite(const cbor_item_t *item)

Is this map indefinite?

param item[borrow]

A map

return

Is this map indefinite?

Reading data

struct cbor_pair *cbor_map_handle(const cbor_item_t *item)

Get the pairs storage.

param item[borrow]

A map

return

Array of cbor_map_size pairs. Manipulation is possible as long as references remain valid.

Creating new items

cbor_item_t *cbor_new_definite_map(size_t size)

Create a new definite map.

param size

The number of slots to preallocate

return

new definite map. NULL on malloc failure.

cbor_item_t *cbor_new_indefinite_map()

Create a new indefinite map.

return

new indefinite map. NULL on malloc failure.

Modifying items

bool cbor_map_add(cbor_item_t *item, struct cbor_pair pair)

Add a pair to the map.

For definite maps, items can only be added to the preallocated space. For indefinite maps, the storage will be expanded as needed

param item[borrow]

A map

param pair[incref]

The key-value pair to add (incref is member-wise)

return

true on success, false if either reallocation failed or the preallocated storage is full