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