nlohamman解析json的问题

Question

使用c++ 解析json, 输出一直是 subit11 is array， 不知道哪里出了问题?

json文件:

{
  "ver": "1.0",
  "login": {
    "user": "zhangsan",
    "pwd": "123456"
  },  
  "data": [
    {   
      "ProjName": "文件夹1-1-1-1-1",
      "FileName": "emp.cdr",
      "ProjNumber": 11, 
      "JpgFile": "emp.jpg",
      "Comments": "cdr for employee",
      "ProjType": "graphic design",
      "ProjState": 1,
      "version": 1,
      "CreateTime": "20230728",
      "UpdateTime": "20230608",
      "id": 8,
      "pid": 6
    },  
    {   
      "ProjName": "文件夹1-1-1-1-2",
      "FileName": "emp.cdr",
      "ProjNumber": 11, 
      "JpgFile": "emp.jpg",
      "Comments": "cdr for employee",
      "ProjType": "graphic design",
      "ProjState": 1,
      "version": 1,
      "CreateTime": "20230728",
      "UpdateTime": "20230608",
      "id": 7,
      "pid": 6
    },  
{
      "ProjName": "文件夹1-1-1-1",
      "FileName": "emp.cdr",
      "ProjNumber": 11,
      "JpgFile": "emp.jpg",
      "Comments": "cdr for employee",
      "ProjType": "graphic design",
      "ProjState": 1,
      "version": 1,
      "CreateTime": "20230728",
      "UpdateTime": "20230608",
      "id": 6,
      "pid": 5
    },  
    {
      "ProjName": "文件夹1-1-1",
      "FileName": "emp.cdr",
      "ProjNumber": 11,
      "JpgFile": "emp.jpg",
      "Comments": "cdr for employee",
      "ProjType": "graphic design",
      "ProjState": 1,
      "version": 1,
      "CreateTime": "20230728",
      "UpdateTime": "20230608",
      "id": 5,
      "pid": 2
    },
    {
      "ProjName": "文件夹1-2-1",
      "FileName": "emp.cdr",
      "ProjNumber": 11,
      "JpgFile": "emp.jpg",
      "Comments": "cdr for employee",
      "ProjType": "graphic design",
      "ProjState": 1,
      "version": 1,
      "CreateTime": "20230728",
      "UpdateTime": "20230608",
      "id": 4,
      "pid": 3
    },

 {
      "ProjName": "文件夹1-2",
      "FileName": "emp.cdr",
      "ProjNumber": 11,
      "JpgFile": "emp.jpg",
      "Comments": "cdr for employee",
      "ProjType": "graphic design",
      "ProjState": 1,
      "version": 1,
      "CreateTime": "20230728",
      "UpdateTime": "20230608",
      "id": 3,
      "pid": 1
    },
    {
      "ProjName": "文件夹1-1",
      "FileName": "emp.cdr",
      "ProjNumber": 11,
      "JpgFile": "emp.jpg",
      "Comments": "cdr for employee",
      "ProjType": "graphic design",
      "ProjState": 1,
      "version": 1,
      "CreateTime": "20230728",
      "UpdateTime": "20230608",
      "id": 2,
      "pid": 1
    },
    {
      "ProjName": "文件夹1",
      "FileName": "emp.cdr",
      "ProjNumber": 11,
      "JpgFile": "emp.jpg",
      "Comments": "cdr for employee",
      "ProjType": "graphic design",
      "ProjState": 1,
      "version": 1,
      "CreateTime": "20230728",
      "UpdateTime": "20230608",
      "id": 1,
      "pid": -1
    }
  ]
}
        

完整c++ 代码:

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include "json.hpp"

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include "ProtocolParser.h"

#include <iostream>
#include <fstream>
#include <string>
#include <vector>

using std::cin;
using std::cout;
using std::endl;
using std::string;
using nlohmann::json;

#define filename "data.json"

bool parsejsonbody(json submit);
 
int main(void)
{
    ifstream file(filename, ios::in | ios::binary);
    if(!file.is_open()){
        throw runtime_error("Faile open the file.");
        }   

    file.seekg(0,ios::end);
    streamsize fileSize = file.tellg();
    if(fileSize <=0){
        throw runtime_error("File is emppty");
        }   

    char *buffer = new char[fileSize];
    
    file.seekg(0,ios::beg);
    file.read(buffer, fileSize);
    cout << fileSize << "filesize" << endl;

   if(!file) {
        throw runtime_error("Reading failed or did not read all data from the file.");
        }   

    file.close();
    ProtocolParser parse;
    json j = parse.doParse(buffer);
    for (auto it = j.begin(); it != j.end(); ++it){
                    if (it->is_string()){
                    string vstr = it.value().get<string>();
                    cout << "it key: " <<  it.key() << endl;
                    cout << "it value: " <<  vstr << endl;
                    }
                    if (it->is_object()){
                    cout << "it is object " << endl;
                    }
    if (it->is_array() || it -> is_object()){
                    cout << "it is array " << endl;
            parsejsonbody(*it);
    }
    }
  return 0;
}

bool parsejsonbody(json subit){
                            for (auto &subit11 :  subit.items()){
                        if (subit11.value().is_string()){
                            cout << "subit11: " <<  *subit11 << endl;
                            string vstri = subit11.value().get<string>();
                             cout << "it key: " <<  subit11.key() << endl;
                             cout << "it value: " <<  vstri << endl;
                            }
                        if (subit11.value().is_array() || subit11.value().is_object()){
                            cout << "subit11 is array " <<   endl;
                            parsejsonbody(subit11);
                            }
                    }}

Answer 1

以下内容来自ChatGPT 4：
在你的C++代码中，你正尝试使用nlohmann::json库来解析一个JSON文件并打印其内容。我注意到了一些可能导致你遇到问题的地方。具体而言，问题出现在如何遍历JSON对象和数组以及如何正确引用subit11。

首先，subit11.value().is_array() || subit11.value().is_object()这一行的递归调用parsejsonbody(subit11);是不正确的。这是因为subit11是一个由subit.items()返回的迭代器项，它的类型是std::pair<const Key, Value>，因此直接传递subit11给parsejsonbody函数是不合适的，应该传递subit11.value()。

其次，当你尝试打印一个字符串时，你使用了*subit11，这是不正确的，因为subit11是一个pair类型，不是指针类型，你不能对它进行解引用操作。应该使用subit11.key()来获取键，使用subit11.value()来获取值。

以下是一些修改后的建议，旨在修正这些问题并改进代码的部分：

#include <fstream>
#include <iostream>
#include <string>
#include "json.hpp"

using json = nlohmann::json;
using namespace std;

bool parsejsonbody(const json& submit);

int main() {
    ifstream file("data.json");
    if (!file.is_open()) {
        cerr << "Failed to open the file." << endl;
        return 1;
    }

    json j;
    file >> j;
    file.close();

    if (j.is_object()) {
        for (auto& el : j.items()) {
            cout << "Key: " << el.key() << endl;
            if (el.value().is_array() || el.value().is_object()) {
                cout << "Processing JSON body..." << endl;
                parsejsonbody(el.value());
            } else if (el.value().is_string()) {
                cout << "Value: " << el.value().get<string>() << endl;
            }
        }
    }

    return 0;
}

bool parsejsonbody(const json& submit) {
    if (submit.is_array()) {
        for (const auto& subItem : submit) {
            for (auto& subIt : subItem.items()) {
                if (subIt.value().is_string()) {
                    cout << "Key: " << subIt.key() << " - Value: " << subIt.value().get<string>() << endl;
                }
            }
        }
    } else if (submit.is_object()) {
        for (auto& subIt : submit.items()) {
            if (subIt.value().is_string()) {
                cout << "Key: " << subIt.key() << " - Value: " << subIt.value().get<string>() << endl;
            } else if (subIt.value().is_array() || subIt.value().is_object()) {
                cout << "Sub-item is a nested object or array" << endl;
                parsejsonbody(subIt.value());
            }
        }
    }
    return true;
}

这个版本的代码进行了以下修改：

1. 直接从文件流中解析JSON，避免了先将文件内容读入字符串再解析的步骤。
2. 在parsejsonbody函数中，增加了对JSON对象和数组的递归处理逻辑。
3. 修正了对subit11的错误引用。

这应该会解决你遇到的“subit11 is array”一直被输出的问题，并能够正确地遍历和打印JSON文件中的所有项。