本节主要介绍RapidJson是如何使用的。

  （1）RapidJson是什么

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()+);

  //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 ;

}
{"key1":"value1","key2":"value2","key3":}

{"key1":"value1","key2":"value_modify","key3":}

  （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 = ;

  vector<string> hobbys = {"语文","数学","英语"};

  map<string,double> score ={{"语文",},{"数学",},{"英语",}};

  // 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 ;

}
{"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 = ;

  vector<string> hobbys = {"语文","数学","英语"};

  map<string,double> scores ={{"语文",},{"数学",},{"英语",}};

  //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 ;

}
{"name":"MenAngel","gender":"boy","age":,"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 = ;

  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() == )

    {

      //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;

  else

    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 ;

}
{"name":"MenAngel","age":,"hobbys":["语文","数学","英语"]}

遍历方法一：

doc 的属性成员有 3个!

.property name is String

.property age is Number

.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 =

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;

  else

    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 ;

}
{"name":"MenAngel","age":,"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() =

doc["hobbys"] is not empty!

Member age is exits!

age:

doc["hobbys"].Capacity() =

doc["name"].length =

doc["name"].length =

doc["test"].length =

doc["test"].length =

    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(  == 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();

  Value b();

  a = b;

  if(b.IsNull())

    cout<<"b is Null,"<<"a = "<<a.GetInt()<<endl;

  Value c(kArrayType);

  Document::AllocatorType& allocator = doc.GetAllocator();

  c.PushBack(Value(), allocator);

  c.PushBack(Value().SetInt(), allocator); // fluent API

  c.PushBack(Value().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();

  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[] = "My first string!";

  f.SetString(str,doc.GetAllocator());

  cout<<f.GetString()<<endl;

  Value g;

  char buffer[];

  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 ;

}
{"name":"MenAngel","age":,"hobbys":["语文","数学","英语"]}

()doc["name"] equal MenAngel!

()doc["name"] equal MenAngel!

()doc["name"] equal MenAngel!

()不成立!

v is Null()

v is Object

tVlaue is not NULL!

tValue is Object

b is Null,a =

c.Capacity() =

c.Size() =

item =

item =

item =

doc["hobbys"].Size() =

doc["hobbys"].Capacity() =

d is not null,e is not null!

d = string e =

My first string!

name -> value

My third String!

my fourth string

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