how to echo directly from dynamic input

[Mijaz]

@jsulm
No input is not a directory it is the string in which I have stored value in about command like this:

QString input = ui->lineEdit_1->text();
ui->lineEdit_2->setText(input);
Now I want to use this "input" in which I already stored value to update my out_altvoltage1_TX_LO_frequency.
//
Detail explenation of my work:
Step 1:
I firstly executed following commands on my board where I am deploying my project like this:

cd /sys/bus/iio/devices/iio:device1/
echo 111111 > out_altvoltage1_TX_LO_frequency
This worked fine;
Step 2:
I create project on my PC using following commands and GUI.

system("cd /sys/bus/iio/devices/iio:device1/; echo 222222 > out_altvoltage1_TX_LO_frequency");
QProcess process1;
process1.start("cat /sys/bus/iio/devices/iio:device1/out_altvoltage1_TX_LO_frequency");
process1.waitForFinished(-1); // will wait forever until finished
QString stdout1 = process1.readAllStandardOutput();
qDebug() << stdout1;
ui->lineEdit_3->setText(stdout1);
This also work correctly.
Step 3:
Now, because it is my task requirement that I need update register (out_altvoltage1_TX_LO_frequency) value at real-time, depends on the situation not remained fixed like (222222), therefore I update code like this:

QString input = ui->lineEdit_1->text();
ui->lineEdit_2->setText(input);
QFile f("/sys/bus/iio/devices/iio:device1/input");
if (f.open(QIODevice::ReadOnly | QIODevice::Text))
{
QByteArray ba = f.readAll();
ui->lineEdit_3->setText(QString(ba));
f.close();
}

whenever I will enter a new value to lineEdit_1 that should update register (out_altvoltage1_TX_LO_frequency) immediately,

this code not working as my requirements.

[jsulm]

@Mijaz OK, that means you want to write to /sys/bus/iio/devices/iio:device1/out_altvoltage1_TX_LO_frequency file, because

cd /sys/bus/iio/devices/iio:device1/
echo 111111 > out_altvoltage1_TX_LO_frequency

does exactly that.
Then simply use QFile to write:

QFile f("/sys/bus/iio/devices/iio:device1/out_altvoltage1_TX_LO_frequency");
if (f.open(QIODevice::WriteOnly | QIODevice::Text)) {
    f.write(ui->lineEdit_2->text().toLatin1());
    f.close();
}

[Mijaz]

@jsulm

QFile f("/sys/bus/iio/devices/iio:device1/out_altvoltage1_TX_LO_frequency");
if (f.open(QIODevice::WriteOnly | QIODevice::Text))
{
f.write(ui->lineEdit_2->text().toLatin1());
f.close();
}

this still not updating register ( out_altvoltage1_TX_LO_frequency) value.

[jsulm]

@Mijaz You still did not answer any of my previous questions?
Did you check what happens? Please use debugger and see whether your if block was executed at all.
Did you check return value of open()?
Did you check what https://doc.qt.io/qt-5/qiodevice.html#errorString returns?

[JonB]

@jsulm
Do you realise this thread is just a rehash of @Mijaz's own https://forum.qt.io/topic/107974/system-vs-process-command/ ? He asks exactly the same question there. You will see the same questions about the cat command and the same answers about using QFile, the same issue about the current directory and paths, .... I tried to help, but he chose not to supply the necessary information, and is just going through the same stuff again. It gets so frustrating here when people choose not to follow through the advice they are given when they do not like it, and instead create a new thread to get the information all over again...

[jsulm]

@JonB Yes, I saw that thread and I agree that it is very frustrating if people do not answer questions and do not follow advices - what's the point to ask then in a forum? But it is how it is...

[Mijaz]

@jsulm
Thank you so much for your kind help to find a proper solution.

[jsulm]

@Mijaz Does it work now?

[Mijaz]

@jsulm
yes, it is working correctly.

[Mijaz]

@jsulm
Now, If I want to update two different register (out_altvoltage0_TX_LO_frequency and out_altvoltage1_TX_LO_frequency ) with same value.
The how can execute code using single QFile .
I tried like follows but not worked:

QFile f("/sys/bus/iio/devices/iio:device1/out_altvoltage0_TX_LO_frequency | out_altvoltage1_TX_LO_frequency");
if (f.open(QIODevice::WriteOnly | QIODevice::Text)) {
f.write(ui->lineEdit_2->text().toLatin1());
f.close();
}

[SGaist]

Hi,

You can't open two files at the same time like that. You can use a loop and open one after the other.