| // Hello World example |
| // This example shows basic usage of DOM-style API. |
| |
| #include "rapidjson/document.h" // rapidjson's DOM-style API |
| #include "rapidjson/prettywriter.h" // for stringify JSON |
| #include <cstdio> |
| |
| using namespace rapidjson; |
| using namespace std; |
| |
| int main(int, char*[]) { |
| //////////////////////////////////////////////////////////////////////////// |
| // 1. Parse a JSON text string to a document. |
| |
| const char json[] = " { \"hello\" : \"world\", \"t\" : true , \"f\" : false, \"n\": null, \"i\":123, \"pi\": 3.1416, \"a\":[1, 2, 3, 4] } "; |
| printf("Original JSON:\n %s\n", json); |
| |
| Document document; // Default template parameter uses UTF8 and MemoryPoolAllocator. |
| |
| #if 0 |
| // "normal" parsing, decode strings to new buffers. Can use other input stream via ParseStream(). |
| if (document.Parse(json).HasParseError()) |
| return 1; |
| #else |
| // In-situ parsing, decode strings directly in the source string. Source must be string. |
| char buffer[sizeof(json)]; |
| memcpy(buffer, json, sizeof(json)); |
| if (document.ParseInsitu(buffer).HasParseError()) |
| return 1; |
| #endif |
| |
| printf("\nParsing to document succeeded.\n"); |
| |
| //////////////////////////////////////////////////////////////////////////// |
| // 2. Access values in document. |
| |
| printf("\nAccess values in document:\n"); |
| assert(document.IsObject()); // Document is a JSON value represents the root of DOM. Root can be either an object or array. |
| |
| assert(document.HasMember("hello")); |
| assert(document["hello"].IsString()); |
| printf("hello = %s\n", document["hello"].GetString()); |
| |
| // Since version 0.2, you can use single lookup to check the existing of member and its value: |
| Value::MemberIterator hello = document.FindMember("hello"); |
| assert(hello != document.MemberEnd()); |
| assert(hello->value.IsString()); |
| assert(strcmp("world", hello->value.GetString()) == 0); |
| (void)hello; |
| |
| assert(document["t"].IsBool()); // JSON true/false are bool. Can also uses more specific function IsTrue(). |
| printf("t = %s\n", document["t"].GetBool() ? "true" : "false"); |
| |
| assert(document["f"].IsBool()); |
| printf("f = %s\n", document["f"].GetBool() ? "true" : "false"); |
| |
| printf("n = %s\n", document["n"].IsNull() ? "null" : "?"); |
| |
| assert(document["i"].IsNumber()); // Number is a JSON type, but C++ needs more specific type. |
| assert(document["i"].IsInt()); // In this case, IsUint()/IsInt64()/IsUint64() also return true. |
| printf("i = %d\n", document["i"].GetInt()); // Alternative (int)document["i"] |
| |
| assert(document["pi"].IsNumber()); |
| assert(document["pi"].IsDouble()); |
| printf("pi = %g\n", document["pi"].GetDouble()); |
| |
| { |
| const Value& a = document["a"]; // Using a reference for consecutive access is handy and faster. |
| assert(a.IsArray()); |
| for (SizeType i = 0; i < a.Size(); i++) // rapidjson uses SizeType instead of size_t. |
| printf("a[%d] = %d\n", i, a[i].GetInt()); |
| |
| int y = a[0].GetInt(); |
| (void)y; |
| |
| // Iterating array with iterators |
| printf("a = "); |
| for (Value::ConstValueIterator itr = a.Begin(); itr != a.End(); ++itr) |
| printf("%d ", itr->GetInt()); |
| printf("\n"); |
| } |
| |
| // Iterating object members |
| static const char* kTypeNames[] = { "Null", "False", "True", "Object", "Array", "String", "Number" }; |
| for (Value::ConstMemberIterator itr = document.MemberBegin(); itr != document.MemberEnd(); ++itr) |
| printf("Type of member %s is %s\n", itr->name.GetString(), kTypeNames[itr->value.GetType()]); |
| |
| //////////////////////////////////////////////////////////////////////////// |
| // 3. Modify values in document. |
| |
| // Change i to a bigger number |
| { |
| uint64_t f20 = 1; // compute factorial of 20 |
| for (uint64_t j = 1; j <= 20; j++) |
| f20 *= j; |
| document["i"] = f20; // Alternate form: document["i"].SetUint64(f20) |
| assert(!document["i"].IsInt()); // No longer can be cast as int or uint. |
| } |
| |
| // Adding values to array. |
| { |
| Value& a = document["a"]; // This time we uses non-const reference. |
| Document::AllocatorType& allocator = document.GetAllocator(); |
| for (int i = 5; i <= 10; i++) |
| a.PushBack(i, allocator); // May look a bit strange, allocator is needed for potentially realloc. We normally uses the document's. |
| |
| // Fluent API |
| a.PushBack("Lua", allocator).PushBack("Mio", allocator); |
| } |
| |
| // Making string values. |
| |
| // This version of SetString() just store the pointer to the string. |
| // So it is for literal and string that exists within value's life-cycle. |
| { |
| document["hello"] = "rapidjson"; // This will invoke strlen() |
| // Faster version: |
| // document["hello"].SetString("rapidjson", 9); |
| } |
| |
| // This version of SetString() needs an allocator, which means it will allocate a new buffer and copy the the string into the buffer. |
| Value author; |
| { |
| char buffer2[10]; |
| int len = sprintf(buffer2, "%s %s", "Milo", "Yip"); // synthetic example of dynamically created string. |
| |
| author.SetString(buffer2, static_cast<SizeType>(len), document.GetAllocator()); |
| // Shorter but slower version: |
| // document["hello"].SetString(buffer, document.GetAllocator()); |
| |
| // Constructor version: |
| // Value author(buffer, len, document.GetAllocator()); |
| // Value author(buffer, document.GetAllocator()); |
| memset(buffer2, 0, sizeof(buffer2)); // For demonstration purpose. |
| } |
| // Variable 'buffer' is unusable now but 'author' has already made a copy. |
| document.AddMember("author", author, document.GetAllocator()); |
| |
| assert(author.IsNull()); // Move semantic for assignment. After this variable is assigned as a member, the variable becomes null. |
| |
| //////////////////////////////////////////////////////////////////////////// |
| // 4. Stringify JSON |
| |
| printf("\nModified JSON with reformatting:\n"); |
| StringBuffer sb; |
| PrettyWriter<StringBuffer> writer(sb); |
| document.Accept(writer); // Accept() traverses the DOM and generates Handler events. |
| puts(sb.GetString()); |
| |
| return 0; |
| } |