JSON read and write values

another_one

Hello!

I have got simple json file:
{
"PORT": "COM3",
"RATE": "BAUD115200",
"PARITY": "PAR_NONE",
"STOPBIT": "STOP_2",
"BITS": "8",
"LD_ADDR": "FFFFFFF085000020",
"ST_ADDR": "FFFFFFF085000020",
"MEM_TYPE": "LWord",
"MEM_ADDR": "FFFFFFF085000000",
"FILE_LOAD": "C:/tmp",
}
And I need to change FILE_LOAD
I read it by the following construction:

 QString strReply = (QString)file_json.readAll();
 QJsonDocument jsonResponse = QJsonDocument::fromJson(strReply.toUtf8());
 QJsonObject jsonObject = jsonResponse.object();

 g_FILE_LOAD = jsonObject.value("FILE_LOAD").toString();
 qDebug()  << "file" << g_FILE_LOAD;

And I see in debug what root is correct
Now I need to change g_FILE_LOAD and store it back

And I don't understand how to do that
The following link unfortunally give an example but in my case I dont use an Array
link text

Please help!

SGaist

Hi,

Why are you doing a C style cast to QString from a QByteArray object ? This is wrong, they are not the same at all. Even more, you turn it back to a QByteArray in the following line.

JonB

@another_one
Did you try

jsonObject["FILE_LOAD"] = newValue;

?

For saving back to file you have to save the whole document back.

mzimmers

@another_one note the final line in this code snippet:

    QByteArray qba = "{ \
                     \"PORT\": \"COM3\", \
                     \"RATE\": \"BAUD115200\", \
                     \"PARITY\": \"PAR_NONE\", \
                     \"STOPBIT\": \"STOP_2\", \
                     \"BITS\": \"8\", \
                     \"LD_ADDR\": \"FFFFFFF085000020\", \
                     \"ST_ADDR\": \"FFFFFFF085000020\", \
                     \"MEM_TYPE\": \"LWord\", \
                     \"MEM_ADDR\": \"FFFFFFF085000000\", \
                     \"FILE_LOAD\": \"C:/tmp\" \
                     }";

    QJsonDocument qjd = QJsonDocument::fromJson(qba);
    QJsonObject qjo = qjd.object();
    qjo["FILE_LOAD"] = "D:/tmp";
    qjd.setObject(qjo);

JonB

@mzimmers said in JSON read and write values:

qjd.setObject(qjo);

Quite right! I find the docs quite unobvious that this is necessary.

another_one

@JonB
Thanks, I tried but I place new line instead of rewriting appropriate value:
"
{
"PORT": "COM3",
"RATE": "BAUD115200",
"PARITY": "PAR_NONE",
"STOPBIT": "STOP_2",
"BITS": "8",
"LD_ADDR": "FFFFFFFF08000020",
"ST_ADDR": "FFFFFFFF08000020",
"MEM_TYPE": "LWord",
"MEM_ADDR": "FFFFFFF085000000",
"FILE_LOAD": "C:/tmp",
}

{
"FILE_LOAD": "C:/temp"
}
{
"FILE_LOAD": "C:/temp"
}
{
"FILE_LOAD": "C:/temp"
}
{
"FILE_LOAD": "C:/temp"
}
{
"FILE_LOAD": "C:/temp"
}
{
"FILE_LOAD": "C:/temp"
}
{
"FILE_LOAD": "C:/temp"
}

"

JonB

@another_one said in JSON read and write values:

I tried but I place new line

I don't know what this means. JSON does not have "new lines".

You asked to "change g_FILE_LOAD and store it back". @mzimmers code is correct for updating the FILE_LOAD item to a new value, and then as I wrote "you have to save the whole document back", i.e. overwrite the existing file with the new QJsonDocument.

another_one

@mzimmers

is it necessary to repeat json context as "constant" in QByteArray, can I use already readed from json file?

JonB

@another_one Yes, of course you can read from file, @mzimmers was just a standalone example.

another_one

@JonB
Now I completely didnt understand)

JonB

@another_one
I don't know what to say to that. Everything is really so straightforward.

Open the file for read, read in the JSON, close the file.
Make the change in memory to the FILE_LOAD value, as per @mzimmers code.
Open the file for write/overwrite, save the JSON, close the file.

another_one

@JonB
ok,
At first I have got the following values in json file:
"
{
"PORT": "COM3",
"RATE": "BAUD115200",
"PARITY": "PAR_NONE",
"STOPBIT": "STOP_2",
"BITS": "8",
"LD_ADDR": "FFFFFFF085000020",
"ST_ADDR": "FFFFFFF085000020",
"MEM_TYPE": "LWord",
"MEM_ADDR": "FFFFFFF085000000",
"FILE_LOAD": "C:/tmp",
}
"

And in code I do the followin:

open json file:

 QFile file_json(QString::fromStdString("monMK.json"));
    if (!file_json.open(QFile::WriteOnly | QFile::Text | QFile::Append)) {
        qDebug() << "json didnt opened";

   }
    else
    {
        qDebug() << "json oponed";
        QString strReply = (QString)file_json.readAll();
        QJsonDocument jsonResponse = QJsonDocument::fromJson(strReply.toUtf8());

Here I ment what my json file is already copied in memory (in jsonResponse), so I close the file:
file_json.close();
Now I do edition:

 QJsonObject jsonObject = jsonResponse.object();
 jsonObject["FILE_LOAD"] = "C:/temp";
jsonResponse.setObject(jsonObject);

And now I store it back:

  file_json.open(QFile::WriteOnly | QFile::Text | QFile::ReadWrite);
  file_json.write(jsonResponse.toJson());

As a result I have got the following jnson file context:
"
{
"FILE_LOAD": "C:/temp"
}
15200",
"PARITY": "PAR_NONE",
"STOPBIT": "STOP_2",
"BITS": "8",
"LD_ADDR": "FFFFFFF085000020",
"ST_ADDR": "FFFFFFF085000020",
"MEM_TYPE": "LWord",
"MEM_ADDR": "FFFFFFF085000000",
"FILE_LOAD": "C:/tmp",
}
"

JonB

@another_one
This is getting crazy. You already had code which read in your JSON from file. Now you open a file for WriteOnly + Append initially, even though we said to open it for read, and then you try to read from it.

Further in the second stage you open a file for WriteOnly + ReadWrite when we said to overwrite.

mzimmers

@another_one your JSON logic now looks OK, but your file handling is wrong.

    QFile qf("./test.json");
    QByteArray qba;
    QJsonParseError qjpe;
    QJsonDocument qjd;

    qf.open(QFile::ReadOnly);
    qba = qf.readAll();
    qf.close();
    qjd = QJsonDocument::fromJson(qba, &qjpe);
    QJsonObject qjo = qjd.object();
    qjo["FILE_LOAD"] = "D:/tmp";
    qjd.setObject(qjo);

    qf.open(QFile::WriteOnly);
    qba = qjd.toJson();
    qf.write(qba);
    qf.close();

SGaist

In addition to what @mzimmers wrote, stop your C style casting. This is very wrong. QByteArray and QString are two very different beasts.

another_one

@SGaist Thank you!

almost everything worked
At the setup ui I write values to JSON file
But when I trying to write during filedialog launched by button clicking its not working

 QFile file_json2(QString::fromStdString("./monMK.json"));
            if (!file_json2.open(QFile::ReadOnly))
            {
                qDebug() << "json didnt opened";
            }
            else
            {
                qDebug() << "json oponed";
                QString strReply2 = (QString)file_json2.readAll();
                qDebug() << strReply2;

                file_json2.close();
                QJsonDocument jsonResponse2 = QJsonDocument::fromJson(strReply2.toUtf8());
                QJsonObject jsonObject2 = jsonResponse2.object();

                jsonObject2["FILE_LOAD"] = g_FILE_LOAD;
                jsonResponse2.setObject(jsonObject2);
                file_json2.open(QFile::WriteOnly);

                file_json2.write(jsonResponse2.toJson());
                qDebug() << "g_FILE_LOAD" << g_FILE_LOAD;
                file_json2.close();
                qDebug() << strReply2;

            }

As I understand its not possible cause of another processing
and I should do JSON file storing by slot function emitted from filedialog of button processing
But I don't undestand how to do an object which has to be as emitter of signal

Please help!

JonB

@another_one
None of the "file dialog" or "slot" or "signal" stuff you mention should be of any relevance. Your code looks like it should work OK. Why don't you say something descriptive rather than "its not working" if you're a programmer and you want help?

another_one

@JonB
Thank you for your replay!

I'm trying to strore the file path in JSON value "FILE_LOAD" in processing of selecting *.bin file in windows folder
To do what I click on "open_folder" button below:

void M_m::on_open_folder_clicked()
{

        QDir dir2;
        dir2.setCurrent(g_FILE_LOAD);
        QString nameFile2 = QFileDialog::getOpenFileName(this, tr("load bin"),"",        tr("*.bin"));
        if (nameFile2.isEmpty())	
        {
            return;
        }
        else
        {
            QFile file;
            file.setFileName(nameFile2);
            ui->lineEdit->setStyleSheet("color: green;  background-color: white");
            ui->lineEdit->setText(nameFile2);
            QFileInfo nameSt(file);
            QString name = nameSt.fileName();
            qDebug()<<"objectNAme="<<file.objectName();//.fileName();
            dir2 = nameSt.dir();//.absoluteDir();
            g_FILE_LOAD = nameFile2;
            qDebug() << QString::number((unsigned int)fls, 16);
            fs2->setValue(3);
        }
}

where fs2->setValue(3); launch Slot function in which I do the following:

  QFile file_json3(QString::fromStdString("monMK.json"));
            if (!file_json3.open(QFile::ReadOnly))
            {
                qDebug() << "json didnt opened";
            }
            else
            {
                qDebug() << "json value3 opened";
                QString strReply3 = (QString)file_json3.readAll();
                qDebug() << strReply3; // read JSON in debug
                QJsonDocument jsonResponse3 = QJsonDocument::fromJson(strReply3.toUtf8());
                QJsonObject jsonObject3 = jsonResponse3.object();
                file_json3.close();
                jsonObject3["FILE_LOAD"] =g_FILE_LOAD;
                jsonResponse3.setObject(jsonObject3);
                file_json3.open(QFile::WriteOnly);
                file_json3.write(jsonResponse3.toJson());
                qDebug() << "g_FILE_LOAD" << "C:/temp"; // g_FILE_LOAD;
                file_json3.close();
                qDebug() << strReply3;
                qDebug() << "store finished";

            }

And only in what case my writing to JSON file is not working
Also I do the almost the same - I store another value from another button clicking in which I use more simplier processing whithout file dialog and it is working
And I compared whese two cases and as result I got the following:
In more simplier case I read JSON in debug and that is correct:
"
json value 1 oponed
QJsonValue(string, "FFFFFFF085000020")
"{\n "BITS": "8",\n "FILE_COMP": "Undefined",\n "FILE_LOAD": "C:/temp",\n "FLOAD": "C:/temp",\n "LD_ADDR": "FFFFFFF085000020",\n "MEM_ADDR": "FFFFFFF085000000",\n "MEM_TYPE": "LWord",\n "PARITY": "PAR_NONE",\n "PORT": "COM3",\n "RATE": "115200",\n "STOPBIT": "STOP_2",\n "ST_ADDR": "FFFFFFF085000000"\n}\n"
"
In case with problem of storing I read JSON in debug and that is not correct:
"
json value3 oponed
"{\n "FILE_LOAD": "C:/tmp",\n "PORT": "PORT20"\n}\n"
g_FILE_LOAD C:/temp
"{\n "FILE_LOAD": "C:/tmp",\n "PORT": "PORT20"\n}\n"
"
And maybe because of what I can not do right writing

So please help to figure out

Thanks!

JonB

@another_one
I don't know. suggest you put qDebug() statements after each line as you change the JSON to see what's going on where. The fact that you use a dialog to get a pathname from the user cannot be relevant.

QString strReply3 = (QString)file_json3.readAll(); do not use this. Use a suitable QString method.

jsulm

@JonB said in JSON read and write values:

do not use this. Use a suitable QString method.

@another_one @SGaist wrote that several times already, don't know why you're not lisening...