jsoncpp使用筆記

1. jsoncpp 中部分函數一覽：

Value類型判斷	值獲取	操作
isNll()（bool類型）	asBool()	數組操作[index]
isBool()	asInt()	isMember(key):bool
isInt()	asString()	數組添加append(value)
isString()	asDouble()	removeMenber(key):Value
isArray()	asArray()	removeIndex(index,value):bool
isObject()	size()

2. jsoncpp讀入文件

#include <string>
#include <json/json.h>
#include <iostream>
#include <fstream>
using namespace std;
 
void readFileJson(); //從文件中讀取JSON，一個存儲了JSON格式字符串的文件
 
int main(int argc, char *argv[]) 
{
	readFileJson();
	
	return 0;
}
 
//從文件中讀取JSON
void readFileJson()
{
	Json::Reader reader;
	Json::Value root;
 
	//從文件中讀取，保證當前文件有test.json文件
	ifstream in("test.json", ios::binary);
	//in.open("test.json", ios::binary);
 
	if( !in.is_open() )  
	{ 
	cout << "Error opening file\n"; 
	return; 
	}
 
	/*
	//test.json內容如下：
	{
		"name":"Tsybius",
		"age":23,
		"sex_is_male":true,
		"partner":
		{
			"partner_name":"Galatea",
			"partner_age":21,
			"partner_sex_is_male":false
		},
		"achievement":["ach1","ach2","ach3"]
	}
	*/
 
	if(reader.parse(in,root))
	{
	//讀取根節點信息
	string name = root["name"].asString();
	int age = root["age"].asInt();
	bool sex_is_male = root["sex_is_male"].asBool();
 
	cout << "My name is " << name << endl;
	cout << "I'm " << age << " years old" << endl;
	cout << "I'm a " << (sex_is_male ? "man" : "woman") << endl;
 
	//讀取子節點信息
	string partner_name = root["partner"]["partner_name"].asString();
	int partner_age = root["partner"]["partner_age"].asInt();
	bool partner_sex_is_male = root["partner"]["partner_sex_is_male"].asBool();
 
	cout << "My partner's name is " << partner_name << endl;
	cout << (partner_sex_is_male ? "he" : "she") << " is "
		<< partner_age << " years old" << endl;
 
	//讀取數組信息
	cout << "Here's my achievements:" << endl;
	for(unsigned int i = 0; i < root["achievement"].size(); i++)
	{
		string ach = root["achievement"][i].asString();
		cout << ach << '\t';
	}
	cout << endl;
 
	cout << "Reading Complete!" << endl;
	}
	else
	{
	cout << "parse error\n" << endl;	
	}
 
	in.close();
}

3.轉載： jsoncpp寫出文件

#include <string>
#include <json/json.h>
#include <iostream>
#include <fstream>
using namespace std;
 
void writeFileJson();//將信息保存爲JSON格式
 
int main(int argc, char *argv[]) 
{
	writeFileJson();
	
	return 0;
}
 
//將信息保存爲JSON格式
void writeFileJson()
{
	//根節點
	Json::Value root;
	
	//根節點屬性
	root["name"] = Json::Value("Mike Jiang");
	root["age"] = Json::Value(23);
	root["sex_is_male"] = Json::Value(true);
	
	//子節點
	Json::Value partner;
	
	//子節點屬性
	partner["partner_name"] = Json::Value("Galatea");
	partner["partner_age"] = Json::Value(21);
	partner["partner_sex_is_male"] = Json::Value(false);
	
	//子節點掛到根節點上
	root["partner"] = Json::Value(partner);
	
	//數組形式
	root["achievement"].append("ach1");
	root["achievement"].append("ach2");
	root["achievement"].append("ach3");
	
	//直接輸出
	cout << "FastWriter:" << endl;
	Json::FastWriter fw;
	cout << fw.write(root) << endl << endl;
	
	//縮進輸出
	cout << "StyledWriter:" << endl;
	Json::StyledWriter sw;
	cout << sw.write(root) << endl << endl;
	
	//輸出到文件
	ofstream os;
	os.open("demo.json");
	os << sw.write(root);
	os.close();
	
	/*
	//json文件內容如下：
	{
		"achievement" : [ "ach1", "ach2", "ach3" ],
		"age" : 23,
		"name" : "Mike Jiang",
		"partner" : {
			"partner_age" : 21,
			"partner_name" : "Galatea",
			"partner_sex_is_male" : false
		},
		"sex_is_male" : true
	}
	*/
 

5. jsoncpp 讀入字符串

#include <string>
#include <json/json.h>
#include <iostream>
#include <fstream>
using namespace std;
 
void readStrJson(); //從字符串中讀取JSON
void readStrProJson(); //從字符串中讀取JSON（內容複雜些）
 
int main(int argc, char *argv[]) 
{
	readStrJson();
	
	cout << "\n\n";
	readStrProJson();
	
	return 0;
}
 
//從字符串中讀取JSON
void readStrJson() 
{
	//字符串
  const char* str = 
      "{\"praenomen\":\"Gaius\",\"nomen\":\"Julius\",\"cognomen\":\"Caezar\","
      "\"born\":-100,\"died\":-44}";
      
  /*
  //json內容如下：
  {
		"praenomen":"Gaius",
		"nomen":"Julius",
		"cognomen":"Caezar",
		"born":-100,
		"died":-44 
	}
  */
 
  Json::Reader reader;
  Json::Value root;
 
  //從字符串中讀取數據
  if(reader.parse(str,root))
  {
      string praenomen = root["praenomen"].asString();
      string nomen = root["nomen"].asString();
      string cognomen = root["cognomen"].asString();
      int born = root["born"].asInt();
      int died = root["died"].asInt();
 
      cout << praenomen + " " + nomen + " " + cognomen
          << " was born in year " << born 
          << ", died in year " << died << endl;
  }
  
}
 
//從字符串中讀取JSON（內容複雜些）
void readStrProJson() 
{
	string strValue = "{\"name\":\"json\",\"array\":[{\"cpp\":\"jsoncpp\"},{\"java\":\"jsoninjava\"},{\"php\":\"support\"}]}";
	/*
	//json內容如下：
	{
    "name": "json″,
    "array": [
        {
            "cpp": "jsoncpp"
        },
        {
            "java": "jsoninjava"
        },
        {
            "php": "support"
        }
    ]
	}
	*/
 
 
	Json::Reader reader;
	Json::Value value;
 
	if (reader.parse(strValue, value))
	{
		string out = value["name"].asString();
		cout << out << endl;
		const Json::Value arrayObj = value["array"];
		for (unsigned int i = 0; i < arrayObj.size(); i++)
		{
			if (!arrayObj[i].isMember("cpp")) 
				continue;
			out = arrayObj[i]["cpp"].asString();
			cout << out;
			if (i != (arrayObj.size() - 1))
				cout << endl;
		}
	}