使用RapidJson在C 中解析一系列对象

Parse an array of objects in C++ using rapidjson

本文关键字：一系列 对象 RapidJson 使用      更新时间：2023-10-16

我正在尝试在C 中解析以下JSON文件。我想迭代"属性"数组，并获得字符串的值："值"的字符串值：该属性对象的"名称"。对于Ex：我想解析此JSON文件并获得"质量"的"值"。

{
"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": ""
    }
]

我正在尝试使用RapidJson库在C 中进行此操作，以解析JSON文件。以下是我对JSON文件解析的实现。我想做的是在for循环中，对于字符串'名称'的特定"值"(for ex：mass(获取字符串的其他"值"，例如'maximutvalue'，'mixumbvalue'，'minimumvalue'，'value'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的解决方案，并访问每个字符串及其值，及其值为属性数组中的每个对象。但是，我想做的是获得任何字符串的值(ex：'maximumValue'，'miximunvalue'，'value'(

如果要获得所选属性的指定属性，则可以使用以下函数：

#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;
}

您可以这样测试：

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";
}
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