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json_object_iterator.h
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/** ******************************************************************************* * @file json_object_iterator.h * * 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. * * @brief 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. * * API attributes: <br> * * Thread-safe: NO<br> * * Reentrant: NO * ******************************************************************************* */ #ifndef JSON_OBJECT_ITERATOR_H #define JSON_OBJECT_ITERATOR_H #include <stddef.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 instance or the "end" iterator value. */ struct json_object_iterator { const void* opaque_; }; /** * forward declaration of json-c'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 json-c 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. * * @warning Any modification of the underlying pair invalidates all * iterators to that pair. * * @param obj JSON Object instance (MUST be of type json_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; * * 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); * } * * @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. * * @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, memorize the "end" iterator prior * to any loop. * * @param obj JSON Object instance (MUST be of type json_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 * * @warning Any modification of the underlying pair * invalidates all iterators to that 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 an invalid or * "end" iterator is passed. * * @return 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. */ const char* json_object_iter_peek_name(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. * * @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 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. */ 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 * * @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 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_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 */