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 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
