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: 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: 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: A map
return: Is this map definite?

bool cbor_map_is_indefinite(const cbor_item_t *item)¶

Is this map indefinite?

param item: 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: 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: Reference to the new map item. The item’s reference count is initialized to one.
return: NULL if memory allocation fails

cbor_item_t *cbor_new_indefinite_map(void)¶

Create a new indefinite map.

return: Reference to the new map item. The item’s reference count is initialized to one.
return: NULL if memory allocation fails

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: A map
param pair: The key-value pair to add. Reference count of the cbor_pair.key and cbor_pair.value will be increased by one.
return: true on success, false if memory allocation failed (indefinite maps) or the preallocated storage is full (definite maps)