Styjun

There is a JSON file, how can I add information there so that the past is left? Did something like this, does not work:

QFile File(pathJSONProject);
File.open(QIODevice::ReadOnly | QIODevice::Text);
QJsonParseError JsonParseError;
QJsonDocument JsonDocument = QJsonDocument::fromJson(File.readAll(), &JsonParseError);

QJsonObject json = JsonDocument.object();

json.insert("Расстояние", dlgOpen->distance);
json.insert("Размер", dlgOpen->size);
json.insert("Путь", pathFolder);
QJsonDocument document(json);
File.open(QFile::WriteOnly | QFile::Text | QFile::Truncate);
File.write(document.toJson());
File.close();

I want to add entries to the file. Can't do it. It does not change.

First, is the file like this? How does he have to add new entries?

 "Name": "45",
 "Path": "C:/Users/Dmitry/Desktop/45.json"

How to add a new entry to the array?

Always handle the return value of QFile::open() to check whether it was successful or not.

There can be multiple ways to insert an array in JSON. Here's an example:

#include <QDebug>
#include <QJsonDocument>
#include <QJsonObject>
#include <QJsonArray>

int main()

 const auto data = R"( "Name": "45", "Path": "C:file.json" )";

 auto doc = QJsonDocument::fromJson( data );
 qDebug() << "BEFORE:nn"
 << qPrintable( doc.toJson( QJsonDocument::Indented ) );

 // Create an array and add objects
 const auto obj1 = QJsonObject "name", "abc" , "default", 11 ;
 const auto obj2 = QJsonObject "name", "xyz" , "default", 22 ;

 auto obj = doc.object();
 obj.insert( "array", QJsonArray obj1, obj2 );

 doc.setObject( obj );
 qDebug() << "nAFTER:n"
 << qPrintable( doc.toJson( QJsonDocument::Indented ) );

 // Add more objects to array

 const auto obj3 = QJsonObject
 
 "name", "def" ,
 "default", 33 ,
 "new1", "1" ,
 "new2", "2" // Add any number of objects...
 ;

 const auto obj4 = QJsonObject "name", "jkl" , "default", 44 ;

 // Get existing array to append more elements
 auto arr = doc.object()[ "array" ].toArray();
 arr.append( obj3 );
 arr.append( obj4 );

 // Set old array to newly updated one
 obj[ "array" ] = arr;

 doc.setObject( obj );
 qDebug() << "nAFTER THAT:n"
 << qPrintable( doc.toJson( QJsonDocument::Indented ) );

 return 0;

Output:

BEFORE:

 
 "Name": "45",
 "Path": "C:file.json"



AFTER:
 
 "Name": "45",
 "Path": "C:file.json",
 "array": [
 
 "default": 11,
 "name": "abc"
 ,
 
 "default": 22,
 "name": "xyz"
 
 ]



AFTER THAT:
 
 "Name": "45",
 "Path": "C:file.json",
 "array": [
 
 "default": 11,
 "name": "abc"
 ,
 
 "default": 22,
 "name": "xyz"
 ,
 
 "default": 33,
 "name": "def",
 "new1": "1",
 "new2": "2"
 ,
 
 "default": 44,
 "name": "jkl"
 
 ]

Also, take a look at QJsonArray::fromStringList() and QJsonArray::fromVariantList().

Check the return value of

File.open(QFile::WriteOnly | QFile::Text | QFile::Truncate);

It's most likely going to be false since you already have the file open for ReadOnly access and haven't closed it.

To modify the data, given your example, you need to check if the contained data in the QJsonDocument is an array or a simple object. In your case, I suppose you want to append data to an array. Try something like this:

// Read the data
const QString filename = "example.json";
QJsonDocument doc = read(filename);

// Check that it's an array and append new data
if (doc.isArray()) 
 auto array = doc.array();
 array.append(QJsonObject
 "Name", "mohabouje", "Path", "whatever"
 );

 array.append(QJsonObject
 "Name", "mojito", "Path", "whatever"
 );
 doc.setArray(array);

// Write the new data
write(filename, doc); 

A helper functions to read/write JSON documents may avoid the mistake of open/closing a file:

QJsonDocument read(const QString& filename) 
 QFile file(filename);
 file.open(QIODevice::ReadOnly 

void write(const QString& filename, const QJsonDocument& document) 
 QFile file(filename);
 file.open(QFile::WriteOnly