How to create read write JSON files in Qt5

Question

Qt5 has a new JSON parser and I want to use it  The problem is that it isn t too clear about what the functions do in layman s terms and how to write code with it  That or I could be reading it wrong  I want to know the code on creating a JSON file in Qt5 and what  quot encapsulates quot  mean

User · Answer

An example on how to use that would be great. There is a couple of examples at the Qt forum, but you're right that the official documentation should be expanded.

QJsonDocument on its own indeed doesn't produce anything, you will have to add the data to it. That's done through the QJsonObject, QJsonArray and QJsonValue classes. The top-level item needs to be either an array or an object (because 1 is not a valid json document, while {foo: 1} is.)

User · Answer

Sadly  many JSON C   libraries have APIs that are non trivial to use  while JSON was intended to be easy to use   So I tried jsoncpp from the gSOAP tools on the JSON doc shown in one of the answers above and this is the code generated with jsoncpp to construct a JSON object in C   which is then written in JSON format to std  cout   value x ctx   x  appDesc    description      SomeDescription   x  appDesc    message      SomeMessage   x  appName    description      Home   x  appName    message      Welcome   x  appName    imp   0     awesome   x  appName    imp   1     best   x  appName    imp   2     good   std  cout  lt  lt  x  lt  lt  std  endl    and this is the code generated by jsoncpp to parse JSON from std  cin and extract its values  replace USE VAL as needed    value x ctx   std  cin  gt  gt  x  if  x soap- gt error    exit EXIT FAILURE      error parsing JSON  define USE VAL path  val  std  cout  lt  lt  path  lt  lt         lt  lt  val  lt  lt  std  endl if  x has  appDesc        if  x  appDesc   has  description        USE VAL    appDesc description   x  appDesc    description       if  x  appDesc   has  message        USE VAL    appDesc message   x  appDesc    message       if  x has  appName        if  x  appName   has  description        USE VAL    appName description   x  appName    description       if  x  appName   has  message        USE VAL    appName message   x  appName    message       if  x  appName   has  imp            for  int i2   0  i2  lt  x  appName    imp   size    i2          USE VAL    appName imp     x  appName    imp   i2            This code uses the JSON C   API of gSOAP 2 8 28  I don t expect people to change libraries  but I think this comparison helps to put JSON C   libraries in perspective

User · Answer

Example  Read json from file     test json          appDesc            description    SomeDescription          message    SomeMessage            appName            description    Home          message    Welcome          imp    awesome   best   good            void readJson              QString val        QFile file        file setFileName  test json          file open QIODevice  ReadOnly   QIODevice  Text         val   file readAll          file close          qWarning    lt  lt  val        QJsonDocument d   QJsonDocument  fromJson val toUtf8           QJsonObject sett2   d object          QJsonValue value   sett2 value QString  appName           qWarning    lt  lt  value        QJsonObject item   value toObject          qWarning    lt  lt  tr  QJsonObject of description      lt  lt  item            in case of string value get value and convert into string         qWarning    lt  lt  tr  QJsonObject appName  of description      lt  lt  item  description          QJsonValue subobj   item  description          qWarning    lt  lt  subobj toString              in case of array get array and convert into string         qWarning    lt  lt  tr  QJsonObject appName  of value      lt  lt  item  imp          QJsonArray test   item  imp   toArray          qWarning    lt  lt  test 1  toString             OUTPUT  QJsonValue object  QJsonObject   description    Home   imp     awesome   best   good    message    YouTube        QJsonObject of description    QJsonObject   description    Home   imp     awesome   best   good    message    YouTube      QJsonObject appName  of description    QJsonValue string   Home     Home    QJsonObject appName  of value    QJsonValue array  QJsonArray   awesome   best   good        best       Example  Read json from string  Assign json to string as below and use the readJson   function shown before   val                   appDesc                description    SomeDescription              message    SomeMessage                    appName                description    Home              message    Welcome              imp    awesome   best   good                        OUTPUT  QJsonValue object  QJsonObject   description    Home   imp     awesome   best   good    message    YouTube        QJsonObject of description    QJsonObject   description    Home   imp     awesome   best   good    message    YouTube      QJsonObject appName  of description    QJsonValue string   Home     Home    QJsonObject appName  of value    QJsonValue array  QJsonArray   awesome   best   good        best

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