轻量简单好用的C++JSON库CJsonObject

1. JSON概述

JSON： JavaScript 对象表示法（ JavaScript Object Notation）。是一种轻量级的数据交换格式。它基于ECMAScript的一个子集。许多编程语言都很容易找到JSON 解析器和 JSON 库。 JSON 文本格式在语法上与创建 JavaScript 对象的代码相同。不同语言的不同json库对json标准的支持不尽相同，为了能让尽可能多的json库都能正常解析和生成json，定义JSON的规范很重要，推荐一个JSON规范《JSON风格指南》。

2. 常用C&C++ JSON库

常用且知名度较高的C&C++的JSON库有cJSON、json-c、JsonCpp等，腾讯员工开源的一个RapidJSON以高性能著称。C&C++的JSON库比较见RapidJSON作者的比较nativejson-benchmark。

3. 非常简单易用的CJsonObject

CJsonObject是基于cJSON全新开发一个C++版的JSON库，CJsonObject的最大优势是轻量（只有4个文件，拷贝到自己代码里即可，无须编译成库，且跨平台和编译器）、简单好用，开发效率极高，对多层嵌套json的读取和生成使用非常简单（大部分json解析库如果要访问多层嵌套json的最里层非常麻烦）。我一直使用的json库是一个较老版本的cJSON，cJSON的好处是简单易用，而且只有两个文件，直接复制到自己的代码中就可以用。cJSON也有一个非常容易让初用者头痛的地方，一不小心就造成内存泄漏了。为此，我基于cJSON封装了一个C++版的CJsonObject，该库比cJSON更简单易用，且只要不是有意不释放内存就不会发生内存泄漏。用CJsonObject的好处在于完全不用文档，看完Demo马上就会用，不明白的看一下头文件就知道，所有函数都十分通俗易懂，最为关键的一点是解析JSON和生成JSON的编码效率非常高。当然，毕竟是经过cJSON封装而来，效率会略低于cJSON，cJSON不支持的CJsonObject也不支持。个人认为，既然已经选了json，那一点点的解析性能差异就不重要了，如果追求性能可以选protobuf。CJsonObject在我最近5年做过的8个项目中广泛应用。CJsonObject非常简单易用，且表现稳定，2018年5月我把它开源https://github.com/Bwar/CJsonObject，并将持续维护。

来看看CJsonObject是如何简单易用：

demo.cpp：

#include <string>

#include <iostream>

#include "../CJsonObject.hpp"

int main()

{

    int iValue;

    std::string strValue;

    neb::CJsonObject oJson("{\"refresh_interval\":60,"

                        "\"dynamic_loading\":["

                            "{"

                                "\"so_path\":\"plugins/User.so\", \"load\":false, \"version\":1,"

                                "\"cmd\":["

                                     "{\"cmd\":2001, \"class\":\"neb::CmdUserLogin\"},"

                                     "{\"cmd\":2003, \"class\":\"neb::CmdUserLogout\"}"

                                "],"

                                "\"module\":["

                                     "{\"path\":\"im/user/login\", \"class\":\"neb::ModuleLogin\"},"

                                     "{\"path\":\"im/user/logout\", \"class\":\"neb::ModuleLogout\"}"

                                "]"

                             "},"

                             "{"

                             "\"so_path\":\"plugins/ChatMsg.so\", \"load\":false, \"version\":1,"

                                 "\"cmd\":["

                                      "{\"cmd\":2001, \"class\":\"neb::CmdChat\"}"

                                 "],"

                             "\"module\":[]"

                             "}"

                        "]"

                    "}");

     std::cout << oJson.ToString() << std::endl;

     std::cout << "-------------------------------------------------------------------" << std::endl;

     std::cout << oJson["dynamic_loading"][]["cmd"][]("class") << std::endl;

     oJson["dynamic_loading"][]["cmd"][].Get("cmd", iValue);

     std::cout << "iValue = " << iValue << std::endl;

     oJson["dynamic_loading"][]["module"][].Get("path", strValue);

     std::cout << "strValue = " << strValue << std::endl;

     std::cout << "-------------------------------------------------------------------" << std::endl;

     oJson.AddEmptySubObject("depend");

     oJson["depend"].Add("nebula", "https://github.com/Bwar/Nebula");

     oJson["depend"].AddEmptySubArray("bootstrap");

     oJson["depend"]["bootstrap"].Add("BEACON");

     oJson["depend"]["bootstrap"].Add("LOGIC");

     oJson["depend"]["bootstrap"].Add("LOGGER");

     oJson["depend"]["bootstrap"].Add("INTERFACE");

     oJson["depend"]["bootstrap"].Add("ACCESS");

     std::cout << oJson.ToString() << std::endl;

     std::cout << "-------------------------------------------------------------------" << std::endl;

     std::cout << oJson.ToFormattedString() << std::endl;

}

Demo执行结果：

[bwar@nebula demo]$ ./CJsonObjectTest

{"refresh_interval":60,"dynamic_loading":[{"so_path":"plugins/User.so","load":false,"version":1,"cmd":[{"cmd":2001,"class":"neb::CmdUserLogin"},{"cmd":2003,"class":"neb::CmdUserLogout"}],"module":[{"path":"im/user/login","class":"neb::ModuleLogin"},{"path":"im/user/logout","class":"neb::ModuleLogout"}]},{"so_path":"plugins/ChatMsg.so","load":false,"version":1,"cmd":[{"cmd":2001,"class":"neb::CmdChat"}],"module":[]}]}

-------------------------------------------------------------------

neb::CmdUserLogout

iValue = 2001

strValue = im/user/login

-------------------------------------------------------------------

{"refresh_interval":60,"dynamic_loading":[{"so_path":"plugins/User.so","load":false,"version":1,"cmd":[{"cmd":2001,"class":"neb::CmdUserLogin"},{"cmd":2003,"class":"neb::CmdUserLogout"}],"module":[{"path":"im/user/login","class":"neb::ModuleLogin"},{"path":"im/user/logout","class":"neb::ModuleLogout"}]},{"so_path":"plugins/ChatMsg.so","load":false,"version":1,"cmd":[{"cmd":2001,"class":"neb::CmdChat"}],"module":[]}],"depend":{"nebula":"https://github.com/Bwar/Nebula","bootstrap":["BEACON","LOGIC","LOGGER","INTERFACE","ACCESS"]}}

-------------------------------------------------------------------

{

	"refresh_interval":	60,

	"dynamic_loading":	[{

			"so_path":	"plugins/User.so",

			"load":	false,

			"version":	1,

			"cmd":	[{

					"cmd":	2001,

					"class":	"neb::CmdUserLogin"

				}, {

					"cmd":	2003,

					"class":	"neb::CmdUserLogout"

				}],

			"module":	[{

					"path":	"im/user/login",

					"class":	"neb::ModuleLogin"

				}, {

					"path":	"im/user/logout",

					"class":	"neb::ModuleLogout"

				}]

		}, {

			"so_path":	"plugins/ChatMsg.so",

			"load":	false,

			"version":	1,

			"cmd":	[{

					"cmd":	2001,

					"class":	"neb::CmdChat"

				}],

			"module":	[]

		}],

	"depend":	{

		"nebula":	"https://github.com/Bwar/Nebula",

		"bootstrap":	["BEACON", "LOGIC", "LOGGER", "INTERFACE", "ACCESS"]

	}

}

再来看看头文件，一看就知道如何使用：

/*******************************************************************************

 * Project:  neb

 * @file     CJsonObject.hpp

 * @brief    Json

 * @author   bwarliao

 * @date:    2014-7-16

 * @note

 * Modify history:

 ******************************************************************************/

#ifndef CJSONOBJECT_HPP_

#define CJSONOBJECT_HPP_

#include <stdio.h>

#include <stddef.h>

#include <malloc.h>

#include <errno.h>

#include <unistd.h>

#include <limits.h>

#include <math.h>

#include <float.h>

#include <string>

#include <map>

#include "cJSON.h"

namespace neb

{

class CJsonObject

{

public:     // method of ordinary json object or json array

    CJsonObject();

    CJsonObject(const std::string& strJson);

    CJsonObject(const CJsonObject* pJsonObject);

    CJsonObject(const CJsonObject& oJsonObject);

    virtual ~CJsonObject();

    CJsonObject& operator=(const CJsonObject& oJsonObject);

    bool operator==(const CJsonObject& oJsonObject) const;

    bool Parse(const std::string& strJson);

    void Clear();

    bool IsEmpty() const;

    bool IsArray() const;

    std::string ToString() const;

    std::string ToFormattedString() const;

    const std::string& GetErrMsg() const

    {

        return(m_strErrMsg);

    }

public:     // method of ordinary json object

    bool AddEmptySubObject(const std::string& strKey);

    bool AddEmptySubArray(const std::string& strKey);

    CJsonObject& operator[](const std::string& strKey);

    std::string operator()(const std::string& strKey) const;

    bool Get(const std::string& strKey, CJsonObject& oJsonObject) const;

    bool Get(const std::string& strKey, std::string& strValue) const;

    bool Get(const std::string& strKey, int32& iValue) const;

    bool Get(const std::string& strKey, uint32& uiValue) const;

    bool Get(const std::string& strKey, int64& llValue) const;

    bool Get(const std::string& strKey, uint64& ullValue) const;

    bool Get(const std::string& strKey, bool& bValue) const;

    bool Get(const std::string& strKey, float& fValue) const;

    bool Get(const std::string& strKey, double& dValue) const;

    bool Add(const std::string& strKey, const CJsonObject& oJsonObject);

    bool Add(const std::string& strKey, const std::string& strValue);

    bool Add(const std::string& strKey, int32 iValue);

    bool Add(const std::string& strKey, uint32 uiValue);

    bool Add(const std::string& strKey, int64 llValue);

    bool Add(const std::string& strKey, uint64 ullValue);

    bool Add(const std::string& strKey, bool bValue, bool bValueAgain);

    bool Add(const std::string& strKey, float fValue);

    bool Add(const std::string& strKey, double dValue);

    bool Delete(const std::string& strKey);

    bool Replace(const std::string& strKey, const CJsonObject& oJsonObject);

    bool Replace(const std::string& strKey, const std::string& strValue);

    bool Replace(const std::string& strKey, int32 iValue);

    bool Replace(const std::string& strKey, uint32 uiValue);

    bool Replace(const std::string& strKey, int64 llValue);

    bool Replace(const std::string& strKey, uint64 ullValue);

    bool Replace(const std::string& strKey, bool bValue, bool bValueAgain);

    bool Replace(const std::string& strKey, float fValue);

    bool Replace(const std::string& strKey, double dValue);

public:     // method of json array

    int GetArraySize();

    CJsonObject& operator[](unsigned int uiWhich);

    std::string operator()(unsigned int uiWhich) const;

    bool Get(int iWhich, CJsonObject& oJsonObject) const;

    bool Get(int iWhich, std::string& strValue) const;

    bool Get(int iWhich, int32& iValue) const;

    bool Get(int iWhich, uint32& uiValue) const;

    bool Get(int iWhich, int64& llValue) const;

    bool Get(int iWhich, uint64& ullValue) const;

    bool Get(int iWhich, bool& bValue) const;

    bool Get(int iWhich, float& fValue) const;

    bool Get(int iWhich, double& dValue) const;

    bool Add(const CJsonObject& oJsonObject);

    bool Add(const std::string& strValue);

    bool Add(int32 iValue);

    bool Add(uint32 uiValue);

    bool Add(int64 llValue);

    bool Add(uint64 ullValue);

    bool Add(int iAnywhere, bool bValue);

    bool Add(float fValue);

    bool Add(double dValue);

    bool AddAsFirst(const CJsonObject& oJsonObject);

    bool AddAsFirst(const std::string& strValue);

    bool AddAsFirst(int32 iValue);

    bool AddAsFirst(uint32 uiValue);

    bool AddAsFirst(int64 llValue);

    bool AddAsFirst(uint64 ullValue);

    bool AddAsFirst(int iAnywhere, bool bValue);

    bool AddAsFirst(float fValue);

    bool AddAsFirst(double dValue);

    bool Delete(int iWhich);

    bool Replace(int iWhich, const CJsonObject& oJsonObject);

    bool Replace(int iWhich, const std::string& strValue);

    bool Replace(int iWhich, int32 iValue);

    bool Replace(int iWhich, uint32 uiValue);

    bool Replace(int iWhich, int64 llValue);

    bool Replace(int iWhich, uint64 ullValue);

    bool Replace(int iWhich, bool bValue, bool bValueAgain);

    bool Replace(int iWhich, float fValue);

    bool Replace(int iWhich, double dValue);

private:

    CJsonObject(cJSON* pJsonData);

private:

    cJSON* m_pJsonData;

    cJSON* m_pExternJsonDataRef;

    std::string m_strErrMsg;

    std::map<unsigned int, CJsonObject*> m_mapJsonArrayRef;

    std::map<std::string, CJsonObject*> m_mapJsonObjectRef;

};

}

#endif /* CJSONHELPER_HPP_ */

如果觉得CJsonObject不错，别忘了给个star，谢谢。