1 // Hello World example
2 // This example shows basic usage of DOM-style API.
3
4 #include "rapidjson/document.h" // rapidjson's DOM-style API
5 #include "rapidjson/prettywriter.h" // for stringify JSON
6 #include <cstdio>
7
8 using namespace rapidjson;
9 using namespace std;
10
main(int,char * [])11 int main(int, char*[]) {
12 ////////////////////////////////////////////////////////////////////////////
13 // 1. Parse a JSON text string to a document.
14
15 const char json[] = " { \"hello\" : \"world\", \"t\" : true , \"f\" : false, \"n\": null, \"i\":123, \"pi\": 3.1416, \"a\":[1, 2, 3, 4] } ";
16 printf("Original JSON:\n %s\n", json);
17
18 Document document; // Default template parameter uses UTF8 and MemoryPoolAllocator.
19
20 #if 0
21 // "normal" parsing, decode strings to new buffers. Can use other input stream via ParseStream().
22 if (document.Parse(json).HasParseError())
23 return 1;
24 #else
25 // In-situ parsing, decode strings directly in the source string. Source must be string.
26 char buffer[sizeof(json)];
27 memcpy(buffer, json, sizeof(json));
28 if (document.ParseInsitu(buffer).HasParseError())
29 return 1;
30 #endif
31
32 printf("\nParsing to document succeeded.\n");
33
34 ////////////////////////////////////////////////////////////////////////////
35 // 2. Access values in document.
36
37 printf("\nAccess values in document:\n");
38 assert(document.IsObject()); // Document is a JSON value represents the root of DOM. Root can be either an object or array.
39
40 assert(document.HasMember("hello"));
41 assert(document["hello"].IsString());
42 printf("hello = %s\n", document["hello"].GetString());
43
44 // Since version 0.2, you can use single lookup to check the existing of member and its value:
45 Value::MemberIterator hello = document.FindMember("hello");
46 assert(hello != document.MemberEnd());
47 assert(hello->value.IsString());
48 assert(strcmp("world", hello->value.GetString()) == 0);
49 (void)hello;
50
51 assert(document["t"].IsBool()); // JSON true/false are bool. Can also uses more specific function IsTrue().
52 printf("t = %s\n", document["t"].GetBool() ? "true" : "false");
53
54 assert(document["f"].IsBool());
55 printf("f = %s\n", document["f"].GetBool() ? "true" : "false");
56
57 printf("n = %s\n", document["n"].IsNull() ? "null" : "?");
58
59 assert(document["i"].IsNumber()); // Number is a JSON type, but C++ needs more specific type.
60 assert(document["i"].IsInt()); // In this case, IsUint()/IsInt64()/IsUInt64() also return true.
61 printf("i = %d\n", document["i"].GetInt()); // Alternative (int)document["i"]
62
63 assert(document["pi"].IsNumber());
64 assert(document["pi"].IsDouble());
65 printf("pi = %g\n", document["pi"].GetDouble());
66
67 {
68 const Value& a = document["a"]; // Using a reference for consecutive access is handy and faster.
69 assert(a.IsArray());
70 for (SizeType i = 0; i < a.Size(); i++) // rapidjson uses SizeType instead of size_t.
71 printf("a[%d] = %d\n", i, a[i].GetInt());
72
73 int y = a[0].GetInt();
74 (void)y;
75
76 // Iterating array with iterators
77 printf("a = ");
78 for (Value::ConstValueIterator itr = a.Begin(); itr != a.End(); ++itr)
79 printf("%d ", itr->GetInt());
80 printf("\n");
81 }
82
83 // Iterating object members
84 static const char* kTypeNames[] = { "Null", "False", "True", "Object", "Array", "String", "Number" };
85 for (Value::ConstMemberIterator itr = document.MemberBegin(); itr != document.MemberEnd(); ++itr)
86 printf("Type of member %s is %s\n", itr->name.GetString(), kTypeNames[itr->value.GetType()]);
87
88 ////////////////////////////////////////////////////////////////////////////
89 // 3. Modify values in document.
90
91 // Change i to a bigger number
92 {
93 uint64_t f20 = 1; // compute factorial of 20
94 for (uint64_t j = 1; j <= 20; j++)
95 f20 *= j;
96 document["i"] = f20; // Alternate form: document["i"].SetUint64(f20)
97 assert(!document["i"].IsInt()); // No longer can be cast as int or uint.
98 }
99
100 // Adding values to array.
101 {
102 Value& a = document["a"]; // This time we uses non-const reference.
103 Document::AllocatorType& allocator = document.GetAllocator();
104 for (int i = 5; i <= 10; i++)
105 a.PushBack(i, allocator); // May look a bit strange, allocator is needed for potentially realloc. We normally uses the document's.
106
107 // Fluent API
108 a.PushBack("Lua", allocator).PushBack("Mio", allocator);
109 }
110
111 // Making string values.
112
113 // This version of SetString() just store the pointer to the string.
114 // So it is for literal and string that exists within value's life-cycle.
115 {
116 document["hello"] = "rapidjson"; // This will invoke strlen()
117 // Faster version:
118 // document["hello"].SetString("rapidjson", 9);
119 }
120
121 // This version of SetString() needs an allocator, which means it will allocate a new buffer and copy the the string into the buffer.
122 Value author;
123 {
124 char buffer[10];
125 int len = sprintf(buffer, "%s %s", "Milo", "Yip"); // synthetic example of dynamically created string.
126
127 author.SetString(buffer, static_cast<size_t>(len), document.GetAllocator());
128 // Shorter but slower version:
129 // document["hello"].SetString(buffer, document.GetAllocator());
130
131 // Constructor version:
132 // Value author(buffer, len, document.GetAllocator());
133 // Value author(buffer, document.GetAllocator());
134 memset(buffer, 0, sizeof(buffer)); // For demonstration purpose.
135 }
136 // Variable 'buffer' is unusable now but 'author' has already made a copy.
137 document.AddMember("author", author, document.GetAllocator());
138
139 assert(author.IsNull()); // Move semantic for assignment. After this variable is assigned as a member, the variable becomes null.
140
141 ////////////////////////////////////////////////////////////////////////////
142 // 4. Stringify JSON
143
144 printf("\nModified JSON with reformatting:\n");
145 StringBuffer sb;
146 PrettyWriter<StringBuffer> writer(sb);
147 document.Accept(writer); // Accept() traverses the DOM and generates Handler events.
148 puts(sb.GetString());
149
150 return 0;
151 }
152