Why I receive error while compiling RapidJSON

问题

Using RapidJSON for parsing a JSON file, I get these errors.

This is part of the JSON file:

{
   "header":{
      "protocolVersion":2,
      "messageID":2,
      "stationID":224
   },
   "cam":{
      "generationDeltaTime":37909,
      "camParameters":{
         "basicContainer":{
            "stationType":5,

This is the code

 doc.Parse(pr);   
           
  
    const auto& header = doc["header"];

    header.protocolVersion = doc["header"]["protocolVersion"].GetInt();   
    header.messageID = doc["header"]["messageID"].GetInt(); 
    header.stationID = doc["header"]["stationID"].GetInt(); 

    
    const auto& cam = doc["cam"];
    
    
    cam.camParameters.basicContainer.stationType = doc["cam"]["camParameters"]["basicContainer"]["stationType"].GetInt();
     
    const auto& referencePosition = doc["cam"]["camParameters"]["basicContainer"]["referencePosition"];

I get this error. I don't know what it says they have no member.

 In member function ‘void MqttApplication::sendm(const std::__cxx11::basic_string<char>&)’:
.cpp:389:12: error: ‘const class rapidjson::GenericValue<rapidjson::UTF8<> >’ has no member named ‘protocolVersion’
  389 |     header.protocolVersion = doc["header"]["protocolVersion"].GetInt();
      |            ^~~~~~~~~~~~~~~
mqtt_application.cpp:390:12: error: ‘const class rapidjson::GenericValue<rapidjson::UTF8<> >’ has no member named ‘messageID’
  390 |     header.messageID = doc["header"]["messageID"].GetInt();
      |            ^~~~~~~~~
mqtt_application.cpp:391:12: error: ‘const class rapidjson::GenericValue<rapidjson::UTF8<> >’ has no member named ‘stationID’
  391 |     header.stationID = doc["header"]["stationID"].GetInt();
      |            ^~~~~~~~~
mqtt_application.cpp:402:9: error: ‘const class rapidjson::GenericValue<rapidjson::UTF8<> >’ has no member named ‘generationDeltaTime’
  402 |     cam.generationDeltaTime = doc["cam"]["generationDeltaTime"].GetInt();
      |         ^~~~~~~~~~~~~~~~~~~
mqtt_application.cpp:405:9: error: ‘const class rapidjson::GenericValue<rapidjson::UTF8<> >’ has no member named ‘camParameters’
  405 |     cam.camParameters.basicContainer.stationType = doc["cam"]["camParameters"]["basicContainer"]["stationType"].GetInt();

回答1:

header is object of rapidjson::Value type and doesn't have protocolVersion, messageID and stationID members. You should provide your custom object type to store values from header. The same goes for other variables (cam and referencePosition). For example:

struct MessageHeader
{
    int protocolVersion;
    int messageID;
    int stationID;
};

//...

const auto& header = doc["header"];

MessageHeader messageHeader;
messageHeader.protocolVersion = header["protocolVersion"].GetInt();
messageHeader.messageID = header["messageID"].GetInt();
messageHeader.stationID = header["stationID"].GetInt();

std::cout << "message header protocol version: " << messageHeader.protocolVersion << std::endl;

来源：https://stackoverflow.com/questions/64839622/why-i-receive-error-while-compiling-rapidjson

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c++

json

parsing

rapidjson