How to use QProcess to show tail command output of a log file on QTextEdit Window?
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There are so many problems in this piece of code, that I don't know where to begin. To name a few:
You are connecting to the signal of an empty QProcess instance, that is not doing anything
In your loadTextFile function, you create a new QProcess on each invokation
That new instance is not the one declared in your class under the same name...
The new process isn't connected to anything
You should really create one QProcess instance, connect to that objects signals, and work from there.
Alternatively, you might look into using QFileSystemWatcher on that file instead of using tail via QProcess.
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You can mimic part of tail -f by holding a QTimer that for example fires every second. In a slot connected to the timout signal of that timer, you just check the still open file for new data and read that.
@
class logFile: QObject (or QWidget) {
public:
logFile(QObject *parent);protected slots:
readData();private:
QTimer timer;
QFile logFile;
QTextStream logStream;
};logFile::logFile(QObject *parent)
{
logFile.setFileName("/var/log/system.log");
logFile.open(QIODevice::ReadOnly|QIODevice::Text);
logStream.setDevice(logFile);
// read the current file contents here if neededconnect(&timer, SIGNAL(timeout()), this, SLOT(readData())); timer.start(1000);}
void logFile::readData()
{
while(!logStream.atEnd()) {
QString line = logStream.readLine();
// supposing logTextEdit is a QPlainTextEdit
ui->logTextEdit->appendPlainText(line);
ui->logTextEdit->appendPlainText("\n");
}
}
@[Brain to terminal, not tested.]
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as suggested i have changed the code and am using QFileSystemWatcher.But i am still not getting the result,i think there is some mistake somewhere in my code,i can't figure out.
Ui form appears for a fraction of second and then the application terminates unexpectedly.
here's the code:-
LOGFILE.h
@
public slots:
void readContents(QString);
@LOGFILE.cpp
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logFile::logFile(QWidget *parent):QMainWindow(parent),ui(new Ui::logFile)
{
QFile *logFile = new QFile("/path/to/log/file");
new QTextStream(logFile);
QFileSystemWatcher fileWatcher = new QFileSystemWatcher(this) ;
fileWatcher->addPath("/path/to/log/file");
QObject::connect(fileWatcher, SIGNAL(fileChanged(QString)), this, SLOT(readContents(QString))) ;
}void logFile::readContents(QString path)
{
QFile *logFile;
QString textAppended ;
int newSize = logFile->size();
int oldSize;
if(newSize > oldSize)
{
if(!logFile->open(QIODevice::ReadOnly))
{
textAppended = "Error in opening the File";
//showOutput();
ui->logTextEdit->setPlainText(textAppended);
return;
}
else
{
logFile->seek((logFile->size() - 1) - (newSize - oldSize));
QTextStream txtStream(logFile);
while(!txtStream.atEnd())
{
textAppended = txtStream.readLine();
}
// showOutput();
ui->logTextEdit->setPlainText(textAppended);
}
oldSize = newSize;
logFile->close();
}
}
@ -
In readContents(), logFile is not initialized. Your program crashes.
In the constructor, you create a QTextStream, but don't keep it anywhere.
May I ask if you have any experience with C++ at all? It dosen't look so, and I would suggest to take the time for some online tutorial on C++ before you continue with Qt.
