diff options
author | Keith Derrick <keith.derrick@palm.com> | 2012-04-12 09:54:21 -0700 |
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committer | Keith Derrick <keith.derrick@palm.com> | 2012-04-12 11:51:23 -0700 |
commit | bcfd1f57ac3aeb6b2ce7af89c3130e617ab6e5c0 (patch) | |
tree | c82d64888f475ca8abc385732001d0d2174e8ef9 /json_object_iterator.h | |
parent | 6917586acfb49d976b9a8a441aaef694a9e2d774 (diff) |
Add alternative iterator implementation
Diffstat (limited to 'json_object_iterator.h')
-rw-r--r-- | json_object_iterator.h | 254 |
1 files changed, 254 insertions, 0 deletions
diff --git a/json_object_iterator.h b/json_object_iterator.h new file mode 100644 index 0000000..21feaf5 --- /dev/null +++ b/json_object_iterator.h @@ -0,0 +1,254 @@ +/** +******************************************************************************* +* @file json_object_iterator.h +* +* Copyright (c) 2009 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. +* +* @brief cjson forces clients to use its private data +* structures for JSON Object iteration. This API +* corrects that by abstracting the private cjson +* details. +* +* The intention is to add this API (and its +* implementation) to Palm's version of the cjson +* library, at which point it can be removed from the +* Wireless System Framework library implementation. +* +* API attributes: +* * Thread-safe: NO +* * Re-entrant: NO +* +******************************************************************************* +*/ + + +#ifndef JSON_OBJECT_ITERATOR_H +#define JSON_OBJECT_ITERATOR_H + +#include <stddef.h> +#include <stdbool.h> + +#ifdef __cplusplus +extern "C" { +#endif + +/** + * Forward declaration for the opaque iterator information. + */ +struct json_object_iter_info_; + +/** + * The opaque iterator that references a name/value pair within + * a JSON Object intance or the "end" iterator value. + */ +struct json_object_iterator { + const void* opaque_; +}; + + +/** + * forward declaration of cjson's JSON value instance structure + */ +struct json_object; + + +/** + * 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). + * + * @code + * struct json_object_iterator iter = json_object_iter_init_default(); + * MyClass() : iter_(json_object_iter_init_default()) + * @endcode + * + * @note The initialized value doesn't reference any specific + * pair, is considered an invalid iterator, and MUST NOT + * be passed to any cjson API that expects a valid + * iterator. + * + * @note User and internal code MUST NOT make any assumptions + * about and dependencies on the value of the "default" + * iterator value. + * + * @return json_object_iterator + */ +struct json_object_iterator +json_object_iter_init_default(void); + +/** Retrieves an iterator to the first pair of the JSON Object. + * + * @note WARNING: Any modification of the underlying pair + * invalidates all iterators to that pair. + * + * @param obj JSON Object instance (MUST be of type + * json_type_object) + * + * @return 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. + * + * @code + * struct json_object_iterator it; + * struct json_object_iterator itEnd; + * struct json_object* obj = json_tokener_parse( + * "{'first':'george', 'age':100}"); + * json_object_iter_begin(obj, &it); + * json_object_iter_end(obj, &itEnd); + * while (!json_object_iter_equal(&it, &itEnd)) { + * printf("%s\n", + * json_object_iter_peek_name(&it)); + * json_object_iter_next(&it); + * } + * + * struct json_object* obj = json_tokener_parse( + * "{'first':'george', 'age':100}"); + * struct json_object_iterator it; + * bool iterable = json_object_iter_begin(&it); + * if (iterable) { + * do { + * printf("%s\n", json_object_iter_peek_name(&it)); + * } while (json_object_iter_next(&it)); + * } + * @endcode + */ +struct json_object_iterator +json_object_iter_begin(struct json_object* obj); + +/** Retrieves the iterator that represents the position beyond the + * last pair of the given JSON Object instance. + * + * @note 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. + * + * @note For performance reasons, memoize the "end" iterator prior + * to any loop. + * + * @param obj JSON Object instance (MUST be of type + * json_type_object) + * + * @return 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) + */ +struct json_object_iterator +json_object_iter_end(const struct json_object* obj); + +/** Returns an iterator to the next pair, if any + * + * @note WARNING: Any modification of the underlying pair + * invalidates all iterators to that pair. + * + * @param iter Iterator that references a name/value pair; + * + * @param 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. + */ +void +json_object_iter_next(struct json_object_iterator* iter); + + +/** Returns a const pointer to the name of the pair referenced + * by the given iterator. + * + * @param 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. + * + * @return const char* Pointer to the name of the rerferenced + * 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. + */ +const char* +json_object_iter_peek_name(const struct json_object_iterator* iter); + + +/** Returns a pointer to the cjson instance representing the + * value of the referenced name/value pair, without altering + * the instance's reference count. + * + * @param 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. + * + * @return struct json_object* Pointer to the cjson 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 cjson node, + * take a look at json_object_get() and + * json_object_put(). IMPORTANT: cjson API represents + * the JSON Null value as a NULL json_object instance + * pointer. + */ +struct json_object* +json_object_iter_peek_value(const struct json_object_iterator* iter); + + +/** 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. + * + * @param iter1 Pointer to first valid, non-NULL iterator + * @param iter2 POinter to second valid, non-NULL iterator + * + * @note 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! + * + * @return 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. + */ +bool +json_object_iter_equal(const struct json_object_iterator* iter1, + const struct json_object_iterator* iter2); + + +#ifdef __cplusplus +} +#endif + + +#endif // JSON_OBJECT_ITERATOR_H |