Question

我试图用c ++解析以下JSON文件。我想重复一下＆＃39;属性＆＃39;数组并获取字符串的值：＆＃39; value＆＃39;对于字符串的特定值：＆＃39; name＆＃39;该属性对象。例如：我想解析这个JSON文件并获得＆＃39;值＆＃39;为了质量＆＃39;。

{
"active": true,
"apiTier": 0,
"attributes": [
    {
        "description": "Given in the datasheet as '0.33 kg (0.73 lbm)'.",
        "maximumValue": "",
        "measurementUnit": "kg",
        "minimumValue": "",
        "name": "mass",
        "productConfiguration": "base",
        "value": "0.33"
    },    
    {
        "description": "",
         "maximumValue": "",
        "measurementUnit": "",
        "minimumValue": "",
        "name": "propellant-type",
        "productConfiguration": "base",
        "value": "hydrazine"
    },
    {
        "description": "Given in the datasheet as 'Thrust/Steady State' and the specified value is also reported as '(0.05-0.230) lbf'.",
        "maximumValue": "1.02",
        "measurementUnit": "N",
        "minimumValue": "0.22",
        "name": "thrust",
        "productConfiguration": "base",
        "value": ""
    }
]

我试图在C ++中使用rapidjson库来解析JSON文件。下面是我解析JSON文件的实现。我想做的是在for循环中，对于一个特定的值＆＃39;一个字符串＆＃39; name＆＃39; （例如：大众）获得其他价值＆＃39;对于字符串，例如＆quot; maximumValue＆＃39;，＆＃39; minimumValue＆＃39;，＆＃39; value＆＃39;等。

#include <fstream>
#include <sstream>
#include <string>
#include <rapidjson/document.h>

int main()
{
   std::ifstream inputFile( "/path/to/json/file/" );
   std::stringstream jsonDocumentBuffer;
   std::string inputLine;

   while ( std::getline( inputFile, inputLine ) )
   {
      jsonDocumentBuffer << inputLine << "\n";
   }
   rapidjson::Document config;
   config.Parse( jsonDocumentBuffer.str( ).c_str( ) );



   assert(config.IsObject()); 

   const rapidjson::Value& attributes   = config["attributes"];
   assert(attributes.IsArray()); 

   int counter = 0; 

   for (rapidjson::Value::ConstValueIterator itr = attributes.Begin(); itr != attributes.End(); ++itr) 
   {
      const rapidjson::Value& attribute = *itr;
      assert(attribute.IsObject()); // each attribute is an object
      for (rapidjson::Value::ConstMemberIterator itr2 = attribute.MemberBegin(); itr2 != attribute.MemberEnd(); ++itr2) 
      {
         std::cout << itr2->name.GetString() << " : " << itr2->value.GetString() << std::endl;
      }
}

编辑1：我找到了一个关于如何迭代属性数组并访问属性数组中每个对象的每个字符串及其值的解决方案。但是，我想要做的是获取任何字符串的值（例如：＆＃39; maximumValue＆＃39;，＆＃39; minimumValue＆＃39;，＆＃39;值＆＃39;）等特定值（ Ex：mass）字符串＆＃39; name＆＃39;。

Answer 1

如果您只想获取所选属性的指定属性，可以使用以下函数：

#include <iostream>
#include <vector>
#include <map>
#include "rapidjson/document.h"

std::map<std::string, std::string> mapForAttributeThatMatchesName(const rapidjson::Value& attributes, const std::string& findMemberName, const std::string& findMemberValue, const std::vector<std::string>& keysToRetrieve) {

    std::map<std::string, std::string> result;
    for (rapidjson::Value::ConstValueIterator itr = attributes.Begin(); itr != attributes.End(); ++itr) {

        const rapidjson::Value::ConstMemberIterator currentAttribute = itr->FindMember(findMemberName.c_str());
        if (currentAttribute != itr->MemberEnd() && currentAttribute->value.IsString()) {

            if (currentAttribute->value == findMemberValue.c_str()) {

                for (auto &keyToRetrieve : keysToRetrieve) {

                    const rapidjson::Value::ConstMemberIterator currentAttributeToReturn = itr->FindMember(keyToRetrieve.c_str());
                    if (currentAttributeToReturn != itr->MemberEnd() && currentAttributeToReturn->value.IsString()) {

                        result[keyToRetrieve] = currentAttributeToReturn->value.GetString();
                    }
                }
                return result;
            }
        }
    }
    return result;
}

你可以这样测试：

const rapidjson::Value& attributes = config["attributes"];
assert(attributes.IsArray());

std::vector<std::string> keysToRetrieve = {"maximumValue", "minimumValue"};
std::map<std::string, std::string> mapForResult = mapForAttributeThatMatchesName(attributes, "name", "mass", keysToRetrieve);
for (auto &mapItem : mapForResult) {

    std::cout << mapItem.first << ":" << mapItem.second << "\n";
}

使用rapidjson在C ++中解析对象数组

1 个答案: