csv file

[micheal15]

I am writing each time on filetmp1 the problem is that when I close the application and I open it again the code will delete the old data

code :

//open csv1
        if(!filetmp.open(QFile::ReadOnly | QFile::Text))
            {
            qDebug()<<"error opening:"<<filetmp.fileName();
            return;
            }

        //open csv2
        QFile filetmp1("c:/Users/LattePanda/Desktop/MOBILTOX/Paramétre_tmp1.csv"); // Vérifiaction l'exsitance de fichier d'indentification
        if(!filetmp1.open(QFile::ReadWrite | QFile::Text))
            {
            qDebug()<<"error opening:"<<filetmp1.fileName();
            return;
            }

        // read header csv1
        QString h1=filetmp.readLine();
        h1=h1.trimmed();  // get rid of ending /n
        qDebug()<<h1;
        // read header csv2
        QString h2=filetmp1.readLine();
        h2=h2.trimmed();
        qDebug()<<h2;

        // get field lists
        QStringList h1List=h1.split(';');
        QStringList h2List=h2.split(';');

        while(!filetmp.atEnd())   // read lines csv1
            {
            QString line=filetmp.readLine();
            line=line.trimmed();
            QStringList val1List=line.split(';');
            QString val2;

            for(const QString h : h2List)   // browse all csv2 fields
                {
                if(h1List.contains(h))  // does it exist in csv1 ?
                    {
                    int index=h1List.indexOf(h); // at what index
                    val2.append(val1List.at(index)); // write value
                    }
                if(h!=h2List.last())
                    val2.append(';');
                }
            val2.append("\n");
            qDebug()<<val2;
            filetmp1.write(val2.toUtf8());
            }
        filetmp.close();
        filetmp1.close();

[jsulm]

@micheal15 said in csv file:

filetmp.open(QFile::ReadOnly | QFile::Text)

Basics, open in append mode:

filetmp.open(QIODeviceBase::ReadOnly | QIODeviceBase::Text | QIODeviceBase::Append)

[micheal15]

@jsulm in fact I will read each time the filetmp and write on filetmp1 i have tried
if(!filetmp1.open(QFile::ReadWrite | QFile::Text | QFile::Append )) but it write nothing on this file

[JonB]

@micheal15
Your code does a read from filetmp1 and later writes to it. Personally I do not like reading from a file and then appending to it without re-opening. If you must I would call seek() before writing to it, a common restriction of read/write IO is that you must seek after changing between reading and writing.

I do not know whether Qt's QFile::Append file open flag guarantees to do this for you. Nor how it interacts with QFile::ReadWrite. Nor what you expect/want to happen if the destination file already has anything more in it than the header line you read.

[jsulm]

@micheal15 said in csv file:

but it write nothing on this file

Then debug your code, there is a reason why there are debugers. What does open(...) return?