Opening file in one function and reading text in other slot(qt)

Question

5.00/5 (1 vote)

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project code is ..

C#

QFile logfile;
bool Candump::openConnection()
{
    QString CandumpFileName = "C:/xamDevelopment/readfiles/P_1.trc";
    QFile logfile(CandumpFileName);

    if (!logfile.open(QIODevice::ReadOnly | QIODevice::Text))
    {
        logger()->error("Error occured while opening CANdump file");
    }
QTimer *CanIOtimer = new QTimer(this);
    CanIOtimer->start(20);
    connect(CanIOtimer, SIGNAL(timeout()), this, SLOT(ReadTextFileData()));
}

Slot is as following

void Candump::ReadTextFileData()
{
 qDebug()<<logfile.isOpen(); //here file is going to close. I want file opened in this slot
}

how i can do this?? please share your experience and knowledge..

What I have tried:

I want to in following step
1: open file
2:start timer
3: connect sink timeout() with slot ReadTextFileData()

in ReadTextFileData
read one line

Posted 23-Jun-16 1:59am

Member 12587659

Updated 23-Jun-16 4:35am

v2

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2 solutions

Solution 1

you must make the logFile a member of the class. The normal way is to declare it in the header or class interface.

Be careful in error handling: check whether the file exists and is open and close it somewhere (destructor).

Tip: Dont use hard code file names and path

Posted 23-Jun-16 2:21am

KarstenK

Comments

Member 12587659 23-Jun-16 8:47am

thanks for your suggestion
I did bbut i am getting error
no match for call to '(qfile) (qstring &)'
in .h FILE -> qFile logfile;
in .cpp file ->
QString CandumpFileName = "C:/XamDevelopment/readfiles/P_1.trc";
logfile(CandumpFileName); //getting error on this line

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Jochen Arndt · Accepted Answer · 2016-06-23T04:35:00

Karsten is right that you should make the QFile a member of a class instead of using a global instance.

But the real problem is that you have a global instance declared on top and use a local instance with the same name in your openConnection function. So the global instance never gets a file name assigned and is never opened.

It should work this way:

C++

#include <qfile>

// Better make this a member of your Candump class
QFile logfile;

bool Candump::openConnection()
{
    QString CandumpFileName = "C:/xamDevelopment/readfiles/P_1.trc";
    // This creates a new (local) QFile instance with the same name as the global one.
    //QFile logfile(CandumpFileName);
    // Use the global / class instance instead:
    logfile.setFileName(CandumpFileName);
 
    if (!logfile.open(QIODevice::ReadOnly | QIODevice::Text))
    {
        logger()->error("Error occured while opening CANdump file");
    }
    // ...
}</qfile>