RapidJson是一个跨平台的c++的json的解析器和生成器；
相比较jsoncpp库，RapidJson只有头文件，容易安装;
RapidJSON 不依赖STL和boost等外部库独立;
只使用如下文件：<cstdio>, <cstdlib>, <cstring>, <inttypes.h>, <new>, <stdint.h>；
高性能，使用模版及内联函数去降低函数调用开销、内部经优化的 Grisu2 及浮点数解析实现、可选的 SSE2/SSE4.2 支持.

（2）RapidJson使用范例(DOM解析json字符串并修改json中指定元素的值)

#include <iostream>
#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"
using namespace std;
using namespace rapidjson;
int main(int argv ,char *argc[])
  //1.把JSON解析至DOM
  const char * strJson = "{\"key1\":\"value1\",\"key2\":\"value2\",\"key3\":100}";
  Document doc;
  doc.Parse(strJson);
  cout<< strJson << endl;
  //2.利用DOM作出修改
  Value& v1 = doc["key2"];
  v1="value_modify";
  //v1.SetString("value_modify");  

  Value& v2 = doc["key3"];
  v2.SetInt(v2.GetInt()+1);
  //SetString()
  //SetBool()
  //SetUint()
  //SetInt64()
  //SetUInt64()
  //SetDouble()
  //SetFloat()
  //SetArray()
  //SetObject()
  //SetNull()
  //3.将DOM stringfy 为json
  StringBuffer buffer;
  Writer<StringBuffer> writer(buffer);
  doc.Accept(writer);
  cout<< buffer.GetString() << endl;
  return 0;
{"key1":"value1","key2":"value2","key3":100}
{"key1":"value1","key2":"value_modify","key3":101}
  （3）文件对象模型（Document Object Model, DOM）API
    文件对象模型，在RapidJson中广泛的使用。
    1.构建json value到DOM：
#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"
using namespace std;
using namespace rapidjson;
int main(int argv ,char *argc[])
  // 1.准备数据
  string name = "MenAngel";
  string gender = "boy";
  int age = 23;
  vector<string> hobbys = {"语文","数学","英语"};
  map<string,double> score ={{"语文",80},{"数学",90},{"英语",100}};
  // 2.初始化DOM
  StringBuffer strBuffer;
  Writer<StringBuffer> writer(strBuffer);
  //2.1 根DOM开始
  writer.StartObject();
    writer.Key("name");
    writer.String(name.c_str());
    writer.Key("gender");
    writer.String(gender.c_str());
    writer.Key("age");
    writer.Int(age);
    writer.Key("hobby");
    writer.StartArray();
    for(auto &item : hobbys)
      writer.String(item.c_str());
    writer.EndArray();
    writer.Key("scores");
    writer.StartObject();
      for(auto &item : scores)
        writer.Key((item.first).c_str());
        writer.Double(item.second);
    writer.EndObject();
  //2.2 根DOM结束
  writer.EndObject();
  //3.将上述DOM组织的json数据写入json.txt文件
  string outFileName = "json.txt";
  ofstream outfile(outFileName,std::ios::trunc);
  outfile<<strBuffer.GetString()<<endl;
  outfile.flush();
  outfile.close();
  return 0;
{"name":"MenAngel","gender":"boy","age":23,"hobbys":["语文","数学","英语"],"scores":{"数学":90.0,"英语":100.0,"语文":80.0}}

    2.构建Json Value到DOM

#include <iostream>
#include <fstream>
#include <vector>
#include <map>
#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"
using namespace std;
using namespace rapidjson;
int main(int argv ,char *argc[])
  // 1.准备数据
  string name = "MenAngel";
  string gender = "boy";
  int age = 23;
  vector<string> hobbys = {"语文","数学","英语"};
  map<string,double> scores ={{"语文",80},{"数学",90},{"英语",100}};
  //2.初始化DOM
  Document doc;
  Document::AllocatorType& allocator = doc.GetAllocator();
  doc.SetObject();//实例化一个GenericValue到根DOM
  Value tempValue1;
  tempValue1.SetString(name.c_str(),allocator);
  doc.AddMember("name",tempValue1,allocator);
  Value tempValue2(rapidjson::kObjectType);
  tempValue2.SetString(gender.c_str(),allocator);
  doc.AddMember("gender",tempValue2,allocator);
  doc.AddMember("age",age,allocator);
  Value tempValue3(kArrayType);
  for(auto hobby:hobbys)
    Value hobbyValue(kStringType);
    hobbyValue.SetString(hobby.c_str(),allocator);
    tempValue3.PushBack(hobbyValue,allocator);
  doc.AddMember("hobbys",tempValue3,allocator);
  Value tempValue4(kObjectType);
  tempValue4.SetObject();
  for(auto score : scores)
    Value scoreValue(kNumberType);
    //cout<<score.second;
    scoreValue.SetInt(score.second);
    Value scoreName(kStringType);
    scoreName.SetString(score.first.c_str(),allocator);
    tempValue4.AddMember(scoreName,scoreValue,allocator);
  doc.AddMember("scores",tempValue4,allocator);
  StringBuffer strBuffer;
  Writer<StringBuffer> writer(strBuffer);
  doc.Accept(writer);
  string outFileName = "json.txt";
  ofstream outfile(outFileName,std::ios::trunc);
  outfile<<strBuffer.GetString()<<endl;
  outfile.flush();
  outfile.close();
  return 0;
{"name":"MenAngel","gender":"boy","age":23,"hobbys":["语文","数学","英语"],"scores":{"数学":90.0,"英语":100.0,"语文":80.0}}
    3.RapidJSon查询




    

#include <iostream>
#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"
using namespace std;
using namespace rapidjson;
int main(int argv,char *argc[])
  //1.构建json
  const char * strJson = "{\"name\":\"MenAngel\",\"age\":23,\"hobbys\":[\"语文\",\"数学\",\"英语\"]}";
  Document doc;
  doc.Parse(strJson);
  StringBuffer strBuffer;
  Writer<StringBuffer> writer(strBuffer);
  doc.Accept(writer);
  cout<<strBuffer.GetString()<<endl;
  //2.查询json值
  cout<<"遍历方法一："<<endl;
  int count = doc.MemberCount();
  cout<<"doc 的属性成员有 "<<count<<"个!"<<endl;
  static const char* kTypeNames[] =
    { "Null", "False", "True", "Object", "Array", "String", "Number" };
  int i = 0;
  for(Value::MemberIterator iter = doc.MemberBegin();iter != doc.MemberEnd();++iter)
    cout<<++i<<".property "<<iter->name.GetString()<<" is "<<kTypeNames[iter->value.GetType()]<<endl;
    if(iter->value.GetType() == 4)
      //3.遍历Array
      for(auto &item : iter->value.GetArray())
        //IsBool、IsObject、IsInt、IsNull、IsNumber、IsDouble
        if(item.IsString())
          cout<<"item = "<<item.GetString()<<endl;
  //4.查询某个成员是否存在
  Value::ConstMemberIterator it = doc.FindMember("scores");
  if(it != doc.MemberEnd())
    cout<<"Has Finded!"<<endl;
    cout<<"Not Finded!"<<endl;
  //5.遍历doc的所有成员
  cout<<"遍历方法二："<<endl;
  for(auto &m :doc.GetObject())
    cout<<"Has member :"<<m.name.GetString()<<" = ";
    if(m.value.IsString())
      cout<<m.value.GetString()<<endl;
    if(m.value.IsInt())
      cout<<m.value.GetInt()<<endl;
    if(m.value.IsBool())
      cout<<m.value.GetBool()<<endl;
    if(m.value.IsArray())
      cout<<"is array"<<endl;
  return 0;
{"name":"MenAngel","age":23,"hobbys":["语文","数学","英语"]}
遍历方法一：
doc 的属性成员有 3个!
1.property name is String
2.property age is Number
3.property hobbys is Array
item = 语文
item = 数学
item = 英语
Not Finded!
遍历方法二：
Has member :name = MenAngel
Has member :age = 23
Has member :hobbys = is array
    4.RapidJson属性获取
#include <iostream>
#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"
using namespace std;
using namespace rapidjson;
int main(int argv,char *argc[])
  //1.构建json
  const char * strJson = "{\"name\":\"MenAngel\",\"age\":23,\"hobbys\":[\"语文\",\"数学\",\"英语\"]}";
  Document doc;
  doc.Parse(strJson);
  StringBuffer strBuffer;
  Writer<StringBuffer> writer(strBuffer);
  doc.Accept(writer);
  cout<<strBuffer.GetString()<<endl;
  //2.DOM根是一个对象
  if(doc.IsObject())
    cout<<"doc is object!"<<endl;
  //3.doc不为j空
  if(!doc.IsNull())
    cout<<"doc is not null!"<<endl;
  Document document;
  if(document.IsNull())
    cout<<"document is null!"<<endl;
    cout<<"Set Object"<<endl;
    document.SetObject();
  if(!document.IsNull())
    cout<<"document is not null!"<<endl;
  //4.DOM 的大小.
  cout<<"doc.MemmberCount() = "<<doc.MemberCount()<<endl;
  //5.增加HasMember判断防止断言错误
  if(doc.HasMember("hobbys") && !doc["hobbys"].Empty())
    cout<<"doc[\"hobbys\"] is not empty!"<<endl;
    cout<<"member not exits!"<<endl;
  //6.取键值
  Value::ConstMemberIterator iter = doc.FindMember("age");
  if(iter != doc.MemberEnd())
    cout<<"Member age is exits!"<<endl;
    cout<<iter->name.GetString()<<":"<<iter->value.GetInt()<<endl;
  //7.Array的大小
  cout<<"doc[\"hobbys\"].Capacity() = "<<doc["hobbys"].Capacity()<<endl;
  //8.字符串的大小 当字符中存在\u0000时strlen会到此截断
  cout<<"doc[\"name\"].length = "<<strlen(doc["name"].GetString())<<endl;
  cout<<"doc[\"name\"].length = "<<doc["name"].GetStringLength()<<endl;
  doc.AddMember("test","a\u0000b",doc.GetAllocator());
  //只能当test成员存在时才能直接赋值
  //doc["test"] = "a\u0000b";
  cout<<"doc[\"test\"].length = "<<strlen(doc["test"].GetString())<<endl;
  cout<<"doc[\"test\"].length = "<<doc["test"].GetStringLength()<<endl;
  return 0;
{"name":"MenAngel","age":23,"hobbys":["语文","数学","英语"]}
doc is object!
doc is not null!
document is null!
Set Object
document is not null!
doc.MemmberCount() = 3
doc["hobbys"] is not empty!
Member age is exits!
age:23
doc["hobbys"].Capacity() = 3
doc["name"].length = 8
doc["name"].length = 8
doc["test"].length = 1
doc["test"].length = 3
    5.RapidJson一些特性




    

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"
using namespace std;
using namespace rapidjson;
int main(int argv,char *argc[])
  //1.构建json
  const char * strJson = "{\"name\":\"MenAngel\",\"age\":23,\"hobbys\":[\"语文\",\"数学\",\"英语\"]}";
  Document doc;
  doc.Parse(strJson);
  StringBuffer strBuffer;
  Writer<StringBuffer> writer(strBuffer);
  doc.Accept(writer);
  cout<<strBuffer.GetString()<<endl;
  //2.const char *、string、value(kStringType)之间比较大小
  if(doc["name"] == "MenAngel")
    cout<<"(1)doc[\"name\"] equal MenAngel!"<<endl;
  if(doc["name"].GetString() == string("MenAngel"))
    cout<<"(2)doc[\"name\"] equal MenAngel!"<<endl;
  if( 0 == strcmp(doc["name"].GetString(),"MenAngel"))
    cout<<"(3)doc[\"name\"] equal MenAngel!"<<endl;
  if(doc["name"].GetString() != "MenAngel")
    cout<<"(4)不成立!"<<endl;
  //3.value赋值
  Value v;//v is NULL && v is not Object
  if(v.IsNull())
    cout<<"v is Null()"<<endl;
  v.SetObject();
  if(v.IsObject())
    cout<<"v is Object"<<endl;
  Value tValue(kObjectType);//tValue is not Null,tValue is  Object
  if(!tValue.IsNull())
    cout<<"tVlaue is not NULL!"<<endl;
  if(tValue.IsObject())
    cout<<"tValue is Object"<<endl;
  //4.转移语义，避免value深赋值
  //AddMember(), PushBack()、赋值均采用深赋值
  Value a(123);
  Value b(456);
  a = b;
  if(b.IsNull())
    cout<<"b is Null,"<<"a = "<<a.GetInt()<<endl;
  Value c(kArrayType);
  Document::AllocatorType& allocator = doc.GetAllocator();
  c.PushBack(Value(11), allocator);
  c.PushBack(Value().SetInt(22), allocator); // fluent API
  c.PushBack(Value(33).Move(), allocator);   // 转移语义
  cout<<"c.Capacity() = "<<c.Capacity()<<endl;
  cout<<"c.Size() = "<<c.Size()<<endl;
  for(auto &m : c.GetArray())
    cout<<"item = "<<m.GetInt()<<endl;
  //字符串的容量及大小
  cout<<"doc[\"hobbys\"].Size() = "<<doc["hobbys"].Size()<<endl;
  cout<<"doc[\"hobbys\"].Capacity() = "<<doc["hobbys"].Capacity()<<endl;
  //5.交换value
  Value d(123);
  Value e("string");
  d.Swap(e);
  if(!d.IsNull() && !e.IsNull())
    cout<<"d is not null,e is not null!"<<endl;
    cout<<"d = "<<d.GetString()<<" e = "<<e.GetInt()<<endl;
  //6.创建string
  //复制字符串
  Value f(kStringType);
  char str[20] = "My first string!";
  f.SetString(str,doc.GetAllocator());
  cout<<f.GetString()<<endl;
  Value g;
  char buffer[20];
  int len = sprintf(buffer, "%s -> %s", "name", "value"); // 动态创建的字符串。
  g.SetString(buffer,len,doc.GetAllocator());
  //g.SetString(buffer,doc.GetAllocator())
  cout<<g.GetString()<<endl;
  //简单引用常量字符串
  Value h;
  h.SetString("My third String!");// h = "My thrid String!"
  cout<<h.GetString()<<endl;
   //简单引用常量l字符串
  Value i;
  const char * tempStr = "my fourth string";
  size_t cstr_len = strlen(tempStr);
  i.SetString(StringRef(tempStr));
  //i.SetString(StringRef(tempStr,cstr_len));
  //i = StringRef(tempStr,cstr_len)
  //i = StringRef(tempStr)
  //i.SetString(tempStr); 不合法
  cout<<i.GetString()<<endl;
  return 0;
{"name":"MenAngel","age":23,"hobbys":["语文","数学","英语"]}
(1)doc["name"] equal MenAngel!
(2)doc["name"] equal MenAngel!
(3)doc["name"] equal MenAngel!
(4)不成立!
v is Null()
v is Object
tVlaue is not NULL!
tValue is Object
b is Null,a = 456
c.Capacity() = 16
c.Size() = 3
item = 11
item = 22
item = 33
doc["hobbys"].Size() = 3
doc["hobbys"].Capacity() = 3
d is not null,e is not null!
d = string e = 123
My first string!
name -> value
My third String!
my fourth string