json_object_iterator.h File Reference

An API for iterating over json_type_object objects, styled to be familiar to C++ programmers. Unlike json_object_object_foreach() and json_object_object_foreachC(), this avoids the need to expose json-c internals like lh_entry. More...

Data Structures
struct	json_object_iterator

Functions
JSON_EXPORT struct json_object_iterator	json_object_iter_init_default (void)
JSON_EXPORT struct json_object_iterator	json_object_iter_begin (struct json_object *obj)
JSON_EXPORT struct json_object_iterator	json_object_iter_end (const struct json_object *obj)
JSON_EXPORT void	json_object_iter_next (struct json_object_iterator *iter)
JSON_EXPORT const char *	json_object_iter_peek_name (const struct json_object_iterator *iter)
JSON_EXPORT struct json_object *	json_object_iter_peek_value (const struct json_object_iterator *iter)
JSON_EXPORT json_bool	json_object_iter_equal (const struct json_object_iterator *iter1, const struct json_object_iterator *iter2)

Detailed Description

An API for iterating over json_type_object objects, styled to be familiar to C++ programmers. Unlike json_object_object_foreach() and json_object_object_foreachC(), this avoids the need to expose json-c internals like lh_entry.

Copyright (c) 2009-2012 Hewlett-Packard Development Company, L.P.

This library is free software; you can redistribute it and/or modify it under the terms of the MIT license. See COPYING for details.

API attributes:

• Thread-safe: NO
  
• Reentrant: NO

Function Documentation

json_object_iter_begin()

JSON_EXPORT struct json_object_iterator json_object_iter_begin

(

struct json_object *

obj

)

Retrieves an iterator to the first pair of the JSON Object.

Warning

Any modification of the underlying pair invalidates all iterators to that pair.

Parameters

obj	JSON Object instance (MUST be of type json_object)

Returns

json_object_iterator If the JSON Object has at least one pair, on return, the iterator refers to the first pair. If the JSON Object doesn't have any pairs, the returned iterator is equivalent to the "end" iterator for the same JSON Object instance.

struct json_object_iterator it;
struct json_object_iterator itEnd;
struct json_object* obj;
 
obj = json_tokener_parse("{'first':'george', 'age':100}");
it = json_object_iter_begin(obj);
itEnd = json_object_iter_end(obj);
 
while (!json_object_iter_equal(&it, &itEnd)) {
    printf("%s\n",
           json_object_iter_peek_name(&it));
    json_object_iter_next(&it);
}

json_object_iter_end()

JSON_EXPORT struct json_object_iterator json_object_iter_end

(

const struct json_object *

obj

)

Retrieves the iterator that represents the position beyond the last pair of the given JSON Object instance.

Warning

Do NOT write code that assumes that the "end" iterator value is NULL, even if it is so in a particular instance of the implementation.

Note

The reason we do not (and MUST NOT) provide "json_object_iter_is_end(json_object_iterator* iter)" type of API is because it would limit the underlying representation of name/value containment (or force us to add additional, otherwise unnecessary, fields to the iterator structure). The "end" iterator and the equality test method, on the other hand, permit us to cleanly abstract pretty much any reasonable underlying representation without burdening the iterator structure with unnecessary data.

For performance reasons, memorize the "end" iterator prior to any loop.

Parameters

obj	JSON Object instance (MUST be of type json_object)

Returns

json_object_iterator On return, the iterator refers to the "end" of the Object instance's pairs (i.e., NOT the last pair, but "beyond the last pair" value)

json_object_iter_equal()

JSON_EXPORT json_bool json_object_iter_equal	(	const struct json_object_iterator *	iter1,
		const struct json_object_iterator *	iter2
	)

Tests two iterators for equality. Typically used to test for end of iteration by comparing an iterator to the corresponding "end" iterator (that was derived from the same JSON Object instance).

Note

The reason we do not (and MUST NOT) provide "json_object_iter_is_end(json_object_iterator* iter)" type of API is because it would limit the underlying representation of name/value containment (or force us to add additional, otherwise unnecessary, fields to the iterator structure). The equality test method, on the other hand, permits us to cleanly abstract pretty much any reasonable underlying representation.

Parameters

iter1	Pointer to first valid, non-NULL iterator
iter2	POinter to second valid, non-NULL iterator

Warning

if a NULL iterator pointer or an uninitialized or invalid iterator, or iterators derived from different JSON Object instances are passed, bad things will happen!

Returns

json_bool non-zero if iterators are equal (i.e., both reference the same name/value pair or are both at "end"); zero if they are not equal.

json_object_iter_init_default()

JSON_EXPORT struct json_object_iterator json_object_iter_init_default

(

void

)

Initializes an iterator structure to a "default" value that is convenient for initializing an iterator variable to a default state (e.g., initialization list in a class' constructor).

struct json_object_iterator iter = json_object_iter_init_default();
MyClass() : iter_(json_object_iter_init_default())

Note

The initialized value doesn't reference any specific pair, is considered an invalid iterator, and MUST NOT be passed to any json-c API that expects a valid iterator.

User and internal code MUST NOT make any assumptions about and dependencies on the value of the "default" iterator value.

Returns

json_object_iterator

json_object_iter_next()

JSON_EXPORT void json_object_iter_next

(

struct json_object_iterator *

iter

)

Returns an iterator to the next pair, if any

Warning

Any modification of the underlying pair invalidates all iterators to that pair.

Parameters

iter

[IN/OUT] Pointer to iterator that references a name/value pair; MUST be a valid, non-end iterator. WARNING: bad things will happen if invalid or "end" iterator is passed. Upon return will contain the reference to the next pair if there is one; if there are no more pairs, will contain the "end" iterator value, which may be compared against the return value of json_object_iter_end() for the same JSON Object instance.

json_object_iter_peek_name()

JSON_EXPORT const char * json_object_iter_peek_name

(

const struct json_object_iterator *

iter

)

Returns a const pointer to the name of the pair referenced by the given iterator.

Parameters

iter	pointer to iterator that references a name/value pair; MUST be a valid, non-end iterator.

Warning

bad things will happen if an invalid or "end" iterator is passed.

Returns

const char* Pointer to the name of the referenced name/value pair. The name memory belongs to the name/value pair, will be freed when the pair is deleted or modified, and MUST NOT be modified or freed by the user.

json_object_iter_peek_value()

JSON_EXPORT struct json_object * json_object_iter_peek_value

(

const struct json_object_iterator *

iter

)

Returns a pointer to the json-c instance representing the value of the referenced name/value pair, without altering the instance's reference count.

Parameters

iter	pointer to iterator that references a name/value pair; MUST be a valid, non-end iterator.

Warning

bad things will happen if invalid or "end" iterator is passed.

Returns

struct json_object* Pointer to the json-c value instance of the referenced name/value pair; the value's reference count is not changed by this function: if you plan to hold on to this json-c node, take a look at json_object_get() and json_object_put(). IMPORTANT: json-c API represents the JSON Null value as a NULL json_object instance pointer.