C++JSON库CJsonObject详解(轻量简单好用)

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"][0]["cmd"][1]("class") << std::endl;
     oJson["dynamic_loading"][0]["cmd"][0].Get("cmd", iValue);
     std::cout << "iValue = " << iValue << std::endl;
     oJson["dynamic_loading"][0]["module"][0].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。