1 /** 2 ******************************************************************************* 3 * @file json_object_iterator.c 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 ******************************************************************************* 11 */ 12 #include "config.h" 13 14 #include <stddef.h> 15 16 #include "json.h" 17 #include "json_object_private.h" 18 19 #include "json_object_iterator.h" 20 21 /** 22 * How It Works 23 * 24 * For each JSON Object, json-c maintains a linked list of zero 25 * or more lh_entry (link-hash entry) structures inside the 26 * Object's link-hash table (lh_table). 27 * 28 * Each lh_entry structure on the JSON Object's linked list 29 * represents a single name/value pair. The "next" field of the 30 * last lh_entry in the list is set to NULL, which terminates 31 * the list. 32 * 33 * We represent a valid iterator that refers to an actual 34 * name/value pair via a pointer to the pair's lh_entry 35 * structure set as the iterator's opaque_ field. 36 * 37 * We follow json-c's current pair list representation by 38 * representing a valid "end" iterator (one that refers past the 39 * last pair) with a NULL value in the iterator's opaque_ field. 40 * 41 * A JSON Object without any pairs in it will have the "head" 42 * field of its lh_table structure set to NULL. For such an 43 * object, json_object_iter_begin will return an iterator with 44 * the opaque_ field set to NULL, which is equivalent to the 45 * "end" iterator. 46 * 47 * When iterating, we simply update the iterator's opaque_ field 48 * to point to the next lh_entry structure in the linked list. 49 * opaque_ will become NULL once we iterate past the last pair 50 * in the list, which makes the iterator equivalent to the "end" 51 * iterator. 52 */ 53 54 /// Our current representation of the "end" iterator; 55 /// 56 /// @note May not always be NULL 57 static const void *kObjectEndIterValue = NULL; 58 59 /** 60 * **************************************************************************** 61 */ 62 struct json_object_iterator json_object_iter_begin(struct json_object *obj) 63 { 64 struct json_object_iterator iter; 65 struct lh_table *pTable; 66 67 /// @note json_object_get_object will return NULL if passed NULL 68 /// or a non-json_type_object instance 69 pTable = json_object_get_object(obj); 70 JASSERT(NULL != pTable); 71 72 /// @note For a pair-less Object, head is NULL, which matches our 73 /// definition of the "end" iterator 74 iter.opaque_ = pTable->head; 75 return iter; 76 } 77 78 /** 79 * **************************************************************************** 80 */ 81 struct json_object_iterator json_object_iter_end(const struct json_object *obj) 82 { 83 struct json_object_iterator iter; 84 85 JASSERT(NULL != obj); 86 JASSERT(json_object_is_type(obj, json_type_object)); 87 88 iter.opaque_ = kObjectEndIterValue; 89 90 return iter; 91 } 92 93 /** 94 * **************************************************************************** 95 */ 96 void json_object_iter_next(struct json_object_iterator *iter) 97 { 98 JASSERT(NULL != iter); 99 JASSERT(kObjectEndIterValue != iter->opaque_); 100 101 iter->opaque_ = ((const struct lh_entry *)iter->opaque_)->next; 102 } 103 104 /** 105 * **************************************************************************** 106 */ 107 const char *json_object_iter_peek_name(const struct json_object_iterator *iter) 108 { 109 JASSERT(NULL != iter); 110 JASSERT(kObjectEndIterValue != iter->opaque_); 111 112 return (const char *)(((const struct lh_entry *)iter->opaque_)->k); 113 } 114 115 /** 116 * **************************************************************************** 117 */ 118 struct json_object *json_object_iter_peek_value(const struct json_object_iterator *iter) 119 { 120 JASSERT(NULL != iter); 121 JASSERT(kObjectEndIterValue != iter->opaque_); 122 123 return (struct json_object *)lh_entry_v((const struct lh_entry *)iter->opaque_); 124 } 125 126 /** 127 * **************************************************************************** 128 */ 129 json_bool json_object_iter_equal(const struct json_object_iterator *iter1, 130 const struct json_object_iterator *iter2) 131 { 132 JASSERT(NULL != iter1); 133 JASSERT(NULL != iter2); 134 135 return (iter1->opaque_ == iter2->opaque_); 136 } 137 138 /** 139 * **************************************************************************** 140 */ 141 struct json_object_iterator json_object_iter_init_default(void) 142 { 143 struct json_object_iterator iter; 144 145 /** 146 * @note Make this a negative, invalid value, such that 147 * accidental access to it would likely be trapped by the 148 * hardware as an invalid address. 149 */ 150 iter.opaque_ = NULL; 151 152 return iter; 153 } 154
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