How to call a variable defined in one function in another function

[jeremy_k]

@Fred-Barclay said in How to call a variable defined in one function in another function:

taz.cpp: In member function ‘void Taz::on_chooseButton_clicked()’:
taz.cpp:40:9: error: ‘cout’ was not declared in this scope
cout << fileNames.at(i);
^
Makefile:945: recipe for target 'taz.o' failed
make: *** [taz.o] Error 1

How should I declare cout?

#include <iostream> and change the reference to std::cout to fix the error reported by the compiler, but that's not going to produce useful results. cout is an output file stream. cout << fileName.at(i) will write one file name at a time to standard output, without a newline or space to separate them. The commented-out process.start("srm" <<cout ) definitely isn't right.

You may want to find a basic C++ tutorial such as http://www.cplusplus.com/doc/tutorial/classes/

[Fred Barclay]

@jeremy_k Thanks - I'll read this more thoroughly in a moment, but the commented-out process.start("srm" <<cout ) is a typo. Fixing now. :)

[mrjj]

hi
Just a note:
The arguments for QProcess should be put in a list

//Example
QString program = "./path/to/srm";
QStringList arguments;
arguments << "file1" << "file 2";
QProcess myProcess(parent);
myProcess.start(program, arguments);

since fileNames is such list, you can use it directly.
as in
myProcess.start(program, fileNames );

Also sorry for cout. what just to write out the names to check
for (int i = 0; i < fileNames.size(); ++i)
cout << fileNames.at(i); // <<< this prints the entry [i] from the list

[Fred Barclay]

@mrjj Would this be correct? I'm just trying to get the contents of fileName echoed into a text file - before I try calling srm -r fileNames with another button.

void Taz::on_chooseButton_clicked()
{
// New behavior
    QFileDialog dialog(this);
    dialog.setViewMode(QFileDialog::Detail);
    dialog.setFileMode(QFileDialog::ExistingFiles);
    QStringList fileNames;
    if (dialog.exec())
        fileNames = dialog.selectedFiles();

    QObject *parent;
    QString program = "/bin/echo";
    QStringList arguments;
    arguments << "fileNames" << ">> /home/fred/fn.txt";
    QProcess *myProcess = new QProcess(parent);
    myProcess->start(program, arguments);

}

When compiling with make I get a warning:

taz.cpp: In member function ‘void Taz::on_chooseButton_clicked()’:
taz.cpp:41:46: warning: ‘parent’ may be used uninitialized in this function [-Wmaybe-uninitialized]
     QProcess *myProcess = new QProcess(parent);

The GUI does finish compiling, though. However, nothing is echoed into /home/fred/fn.txt. :(
Thanks!

[mrjj]

Hi
well, this is not ok.
QObject *parent;
..
QProcess *myProcess = new QProcess(parent);
as parent is a dangling pointer so its invalid to do.
( its just points to random location)
( that is what it means with warning: ‘parent’ may be used uninitialized)
so just use
QProcess *myProcess = new QProcess(this); // this being Taz ( mainwinow i guess)

also, you are not really processing the list
but you should get "fileNames" in the fn.txt?

maybe you can do
fileNames << ">> /home/fred/fn.txt";
and
myProcess->start(program, fileNames );

But in any case
"fileNames" do not expand to the real list as it would in say bash.
it just is text. like "hello".

[Fred Barclay]

@mrjj Thanks - unallocated error fixed. You're right, I'm definitely not processing the list fileNames. I was just hoping I could get something (even the word "fileNames") to be echoed into a file.

This yields nothing; is it what you are talking about?

void Taz::on_chooseButton_clicked()
{
// New behavior
    QFileDialog dialog(this);
    dialog.setViewMode(QFileDialog::Detail);
    dialog.setFileMode(QFileDialog::ExistingFiles);
    QStringList fileNames;
    if (dialog.exec())
        fileNames = dialog.selectedFiles();

    QString program = "/bin/echo";
    QStringList arguments;
    fileNames << ">> /home/fred/fn.txt";
    QProcess *myProcess = new QProcess(this);
    myProcess->start(program, fileNames );
}

BTW: here is my entire taz.cpp file: https://gist.github.com/Fred-Barclay/f0454d31681fe3744659cd18dfd62403

and here is a screenshot (just in case...)

[mrjj]

Hi
it looks ok now.

you should use qDebug() to check stuff out
(#include <QDebug>)

and do
qDebug() << " numfiles:" << fileNames.size();
It will show in Creator in output window.
Should give you a non zero value.

also
QProcess has a error() function u should also call to see if any errors.

for test u can also try
QProcess sh;
sh.start("sh", QStringList() << "-c" << "ifconfig" << ">> /home/fred/fn.txt");

[SGaist]

Hi,

IIRC, you should split >> and /home/fred/fn.txt and add both separately to your argument list.

[Fred Barclay]

@SGaist Hmm... that would make sense but even then nothing seems to happen when or after I press the button ("Choose File" in the screenshot above):

void Taz::on_chooseButton_clicked()
{
// New behavior
    QFileDialog dialog(this);
    dialog.setViewMode(QFileDialog::Detail);
    dialog.setFileMode(QFileDialog::ExistingFiles);
    QStringList fileNames;
    if (dialog.exec())
        fileNames = dialog.selectedFiles();

    QString program = "/bin/echo";
    QStringList arguments;
    arguments << "fileName" << ">>" << "/home/fred/fn.txt";
    QProcess *myProcess = new QProcess(this);
    myProcess->start(program, arguments);
}

[SGaist]

You should add some error checking to your code. That would help pinpoint the problem.

[jeremy_k]

@Fred-Barclay said in How to call a variable defined in one function in another function:

@SGaist Hmm... that would make sense but even then nothing seems to happen when or after I press the button ("Choose File" in the screenshot above):

void Taz::on_chooseButton_clicked()
{
// New behavior
    QFileDialog dialog(this);
    dialog.setViewMode(QFileDialog::Detail);
    dialog.setFileMode(QFileDialog::ExistingFiles);
    QStringList fileNames;
    if (dialog.exec())
        fileNames = dialog.selectedFiles();

    QString program = "/bin/echo";
    QStringList arguments;
    arguments << "fileName" << ">>" << "/home/fred/fn.txt";
    QProcess *myProcess = new QProcess(this);
    myProcess->start(program, arguments);
}

Is the expectation that "fileName" will be appended to the file /home/fred/fn.txt?

Neither echo nor QProcess have special handling for ">>" as far as I am aware. Redirection to a file using this syntax is usually the domain of a shell such as bash. QProcess either redirects output to the enclosing program's output, or makes it available via QProcess::readChannel().

What you'll get instead is the string "fileName >> /home/fred/fn.txt" written to standard output.

#include <QCoreApplication>
#include <iostream>
#include <QProcess>
#include <QObject>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QProcess p;
    p.setProcessChannelMode(QProcess::ForwardedChannels);
    QStringList arguments;
    arguments << "fileName" << ">>" << "/home/fred/fn.txt";
    QObject::connect<void(QProcess::*)(int)>(&p, &QProcess::finished, [=](){ std::cout << "process done" << std::endl; });
    p.start("/bin/echo", arguments);

    return a.exec();
}

[mjsurette]

Hi. For a non c++ programmer, you seem to be catching on. Your posting of...

void Taz::on_chooseButton_clicked()
{
// New behavior
    QFileDialog dialog(this);
    dialog.setViewMode(QFileDialog::Detail);
    dialog.setFileMode(QFileDialog::ExistingFiles);
    QStringList fileNames;
    if (dialog.exec())
        fileNames = dialog.selectedFiles();

    QString program = "/bin/echo";
    QStringList arguments;
    arguments << "fileName" << ">>" << "/home/fred/fn.txt";
    QProcess *myProcess = new QProcess(this);
    myProcess->start(program, arguments);
}

isn't too bad. Just a little overly complex, so this

void Taz::on_chooseButton_clicked()
{
// New behavior
    QFileDialog dialog(this);
    dialog.setViewMode(QFileDialog::Detail);
    dialog.setFileMode(QFileDialog::ExistingFiles);
    QStringList fileNames;
    if (dialog.exec())
    {
        fileNames = dialog.selectedFiles();
        QProcess::execute("echo", fileNames);
    }
}

should echo the filenames to your Application Output screen. This is actually a lot closer to what you're end game should look like.

HTH

Mike