1 /** 2 ******************************************************************************* 3 * @file json_object_iterator.h 4 * 5 * Copyright (c) 2009-2012 Hewlett-Packard Development Company, L.P. 6 * 7 * This library is free software; you can redistribute it and/or modify 8 * it under the terms of the MIT license. See COPYING for details. 9 * 10 * @brief json-c forces clients to use its private data 11 * structures for JSON Object iteration. This API 12 * corrects that by abstracting the private json-c 13 * details. 14 * 15 * API attributes: <br> 16 * * Thread-safe: NO<br> 17 * * Reentrant: NO 18 * 19 ******************************************************************************* 20 */ 21 22 23 #ifndef JSON_OBJECT_ITERATOR_H 24 #define JSON_OBJECT_ITERATOR_H 25 26 #include <stddef.h> 27 28 #ifdef __cplusplus 29 extern "C" { 30 #endif 31 32 /** 33 * Forward declaration for the opaque iterator information. 34 */ 35 struct json_object_iter_info_; 36 37 /** 38 * The opaque iterator that references a name/value pair within 39 * a JSON Object instance or the "end" iterator value. 40 */ 41 struct json_object_iterator { 42 const void* opaque_; 43 }; 44 45 46 /** 47 * forward declaration of json-c's JSON value instance structure 48 */ 49 struct json_object; 50 51 52 /** 53 * Initializes an iterator structure to a "default" value that 54 * is convenient for initializing an iterator variable to a 55 * default state (e.g., initialization list in a class' 56 * constructor). 57 * 58 * @code 59 * struct json_object_iterator iter = json_object_iter_init_default(); 60 * MyClass() : iter_(json_object_iter_init_default()) 61 * @endcode 62 * 63 * @note The initialized value doesn't reference any specific 64 * pair, is considered an invalid iterator, and MUST NOT 65 * be passed to any json-c API that expects a valid 66 * iterator. 67 * 68 * @note User and internal code MUST NOT make any assumptions 69 * about and dependencies on the value of the "default" 70 * iterator value. 71 * 72 * @return json_object_iterator 73 */ 74 struct json_object_iterator 75 json_object_iter_init_default(void); 76 77 /** Retrieves an iterator to the first pair of the JSON Object. 78 * 79 * @warning Any modification of the underlying pair invalidates all 80 * iterators to that pair. 81 * 82 * @param obj JSON Object instance (MUST be of type json_object) 83 * 84 * @return json_object_iterator If the JSON Object has at 85 * least one pair, on return, the iterator refers 86 * to the first pair. If the JSON Object doesn't 87 * have any pairs, the returned iterator is 88 * equivalent to the "end" iterator for the same 89 * JSON Object instance. 90 * 91 * @code 92 * struct json_object_iterator it; 93 * struct json_object_iterator itEnd; 94 * struct json_object* obj; 95 * 96 * obj = json_tokener_parse("{'first':'george', 'age':100}"); 97 * it = json_object_iter_begin(obj); 98 * itEnd = json_object_iter_end(obj); 99 * 100 * while (!json_object_iter_equal(&it, &itEnd)) { 101 * printf("%s\n", 102 * json_object_iter_peek_name(&it)); 103 * json_object_iter_next(&it); 104 * } 105 * 106 * @endcode 107 */ 108 struct json_object_iterator 109 json_object_iter_begin(struct json_object* obj); 110 111 /** Retrieves the iterator that represents the position beyond the 112 * last pair of the given JSON Object instance. 113 * 114 * @warning Do NOT write code that assumes that the "end" 115 * iterator value is NULL, even if it is so in a 116 * particular instance of the implementation. 117 * 118 * @note The reason we do not (and MUST NOT) provide 119 * "json_object_iter_is_end(json_object_iterator* iter)" 120 * type of API is because it would limit the underlying 121 * representation of name/value containment (or force us 122 * to add additional, otherwise unnecessary, fields to 123 * the iterator structure). The "end" iterator and the 124 * equality test method, on the other hand, permit us to 125 * cleanly abstract pretty much any reasonable underlying 126 * representation without burdening the iterator 127 * structure with unnecessary data. 128 * 129 * @note For performance reasons, memorize the "end" iterator prior 130 * to any loop. 131 * 132 * @param obj JSON Object instance (MUST be of type json_object) 133 * 134 * @return json_object_iterator On return, the iterator refers 135 * to the "end" of the Object instance's pairs 136 * (i.e., NOT the last pair, but "beyond the last 137 * pair" value) 138 */ 139 struct json_object_iterator 140 json_object_iter_end(const struct json_object* obj); 141 142 /** Returns an iterator to the next pair, if any 143 * 144 * @warning Any modification of the underlying pair 145 * invalidates all iterators to that pair. 146 * 147 * @param iter [IN/OUT] Pointer to iterator that references a 148 * name/value pair; MUST be a valid, non-end iterator. 149 * WARNING: bad things will happen if invalid or "end" 150 * iterator is passed. Upon return will contain the 151 * reference to the next pair if there is one; if there 152 * are no more pairs, will contain the "end" iterator 153 * value, which may be compared against the return value 154 * of json_object_iter_end() for the same JSON Object 155 * instance. 156 */ 157 void 158 json_object_iter_next(struct json_object_iterator* iter); 159 160 161 /** Returns a const pointer to the name of the pair referenced 162 * by the given iterator. 163 * 164 * @param iter pointer to iterator that references a name/value 165 * pair; MUST be a valid, non-end iterator. 166 * 167 * @warning bad things will happen if an invalid or 168 * "end" iterator is passed. 169 * 170 * @return const char* Pointer to the name of the referenced 171 * name/value pair. The name memory belongs to the 172 * name/value pair, will be freed when the pair is 173 * deleted or modified, and MUST NOT be modified or 174 * freed by the user. 175 */ 176 const char* 177 json_object_iter_peek_name(const struct json_object_iterator* iter); 178 179 180 /** Returns a pointer to the json-c instance representing the 181 * value of the referenced name/value pair, without altering 182 * the instance's reference count. 183 * 184 * @param iter pointer to iterator that references a name/value 185 * pair; MUST be a valid, non-end iterator. 186 * 187 * @warning bad things will happen if invalid or 188 * "end" iterator is passed. 189 * 190 * @return struct json_object* Pointer to the json-c value 191 * instance of the referenced name/value pair; the 192 * value's reference count is not changed by this 193 * function: if you plan to hold on to this json-c node, 194 * take a look at json_object_get() and 195 * json_object_put(). IMPORTANT: json-c API represents 196 * the JSON Null value as a NULL json_object instance 197 * pointer. 198 */ 199 struct json_object* 200 json_object_iter_peek_value(const struct json_object_iterator* iter); 201 202 203 /** Tests two iterators for equality. Typically used to test 204 * for end of iteration by comparing an iterator to the 205 * corresponding "end" iterator (that was derived from the same 206 * JSON Object instance). 207 * 208 * @note The reason we do not (and MUST NOT) provide 209 * "json_object_iter_is_end(json_object_iterator* iter)" 210 * type of API is because it would limit the underlying 211 * representation of name/value containment (or force us 212 * to add additional, otherwise unnecessary, fields to 213 * the iterator structure). The equality test method, on 214 * the other hand, permits us to cleanly abstract pretty 215 * much any reasonable underlying representation. 216 * 217 * @param iter1 Pointer to first valid, non-NULL iterator 218 * @param iter2 POinter to second valid, non-NULL iterator 219 * 220 * @warning if a NULL iterator pointer or an uninitialized 221 * or invalid iterator, or iterators derived from 222 * different JSON Object instances are passed, bad things 223 * will happen! 224 * 225 * @return json_bool non-zero if iterators are equal (i.e., both 226 * reference the same name/value pair or are both at 227 * "end"); zero if they are not equal. 228 */ 229 json_bool 230 json_object_iter_equal(const struct json_object_iterator* iter1, 231 const struct json_object_iterator* iter2); 232 233 234 #ifdef __cplusplus 235 } 236 #endif 237 238 239 #endif /* JSON_OBJECT_ITERATOR_H */ 240
