C++构造和解析JSON

JSON是一种轻量级的数据交互格式，易于人阅读和编写，同时也易于机器解析和生成，并有效地提升网络传输效率，实际项目中经常用到，相比xml有很多优点，问问度娘，优点一箩筐。

第三方库

json解析选用jsoncpp作为第三方库，jsoncpp使用广泛，c++开发首选。

jsoncpp目前已经托管到了github上，地址：https://github.com/open-source-parsers/jsoncpp

使用

使用c++进行构造json和解析json，选用vs2010作为IDE。工程中使用jsoncpp的源码进行编译，没有使用jsoncpp的库，为方便大家使用把dll和lib库也放到了我的工程jsoncpplib文件夹下，有需要的可以直接引用库。

待解析的json数据格式如下图：

/********************************************************
Copyright (C), 2016-2017,
FileName: 	main
Author: 	woniu201
Email: 		wangpengfei.201@163.com
Created: 	2017/09/06
Description:use jsoncpp src , not use dll, but i also provide dll and lib.
********************************************************/

#include "stdio.h"
#include <string>
#include "jsoncpp/json.h"

using namespace std;

/************************************
@ Brief:		read file
@ Author:		woniu201
@ Created: 		2017/09/06
@ Return:		file data
************************************/
char *getfileAll(char *fname)
{
	FILE *fp;
	char *str;
	char txt[1000];
	int filesize;
	if ((fp=fopen(fname,"r"))==NULL){
		printf("open file %s fail \n",fname);
		return NULL;
	}

	fseek(fp,0,SEEK_END); 

	filesize = ftell(fp);
	str=(char *)malloc(filesize);
	str[0]=0;

	rewind(fp);
	while((fgets(txt,1000,fp))!=NULL){
		strcat(str,txt);
	}
	fclose(fp);
	return str;
}

/************************************
@ Brief:		write file
@ Author:		woniu201
@ Created: 		2017/09/06
@ Return:
************************************/
int writefileAll(char* fname,const char* data)
{
	FILE *fp;
	if ((fp=fopen(fname, "w")) == NULL)
	{
		printf("open file %s fail \n", fname);
		return 1;
	}

	fprintf(fp, "%s", data);
	fclose(fp);

	return 0;
}

/************************************
@ Brief:		parse json data
@ Author:		woniu201
@ Created: 		2017/09/06
@ Return:
************************************/
int parseJSON(const char* jsonstr)
{
	Json::Reader reader;
	Json::Value  resp;

	if (!reader.parse(jsonstr, resp, false))
	{
		printf("bad json format!\n");
		return 1;
	}
	int result = resp["Result"].asInt();
	string resultMessage = resp["ResultMessage"].asString();
	printf("Result=%d; ResultMessage=%s\n", result, resultMessage.c_str());

	Json::Value & resultValue = resp["ResultValue"];
	for (int i=0; i<resultValue.size(); i++)
	{
		Json::Value subJson = resultValue[i];
		string cpuRatio = subJson["cpuRatio"].asString();
		string serverIp = subJson["serverIp"].asString();
		string conNum = subJson["conNum"].asString();
		string websocketPort = subJson["websocketPort"].asString();
		string mqttPort = subJson["mqttPort"].asString();
		string ts = subJson["TS"].asString();

		printf("cpuRatio=%s; serverIp=%s; conNum=%s; websocketPort=%s; mqttPort=%s; ts=%s\n",cpuRatio.c_str(), serverIp.c_str(),
			conNum.c_str(), websocketPort.c_str(), mqttPort.c_str(), ts.c_str());
	}
	return 0;
}

/************************************
@ Brief:		create json data
@ Author:		woniu201
@ Created: 		2017/09/06
@ Return:
************************************/
int createJSON()
{
	Json::Value req;
	req["Result"] = 1;
	req["ResultMessage"] = "200";

	Json::Value	object1;
	object1["cpuRatio"] = "4.04";
	object1["serverIp"] = "42.159.116.104";
	object1["conNum"] = "1";
	object1["websocketPort"] = "0";
	object1["mqttPort"] = "8883";
	object1["TS"] = "1504665880572";
	Json::Value	object2;
	object2["cpuRatio"] = "2.04";
	object2["serverIp"] = "42.159.122.251";
	object2["conNum"] = "2";
	object2["websocketPort"] = "0";
	object2["mqttPort"] = "8883";
	object2["TS"] = "1504665896981";

	Json::Value jarray;
	jarray.append(object1);
	jarray.append(object2);

	req["ResultValue"] = jarray;

	Json::FastWriter writer;
	string jsonstr = writer.write(req);

	printf("%s\n", jsonstr.c_str());

	writefileAll("createJson.json", jsonstr.c_str());
	return 0;
}

int main()
{
	char* json = getfileAll("parseJson.json");
	parseJSON(json);
	printf("===============================\n");
	createJSON();

	getchar();
	return 1;
}

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