Qt program crash why?

ChrisW67

@Wasee Could you please put your code in tags so the forum treats it as code. You start or end a code block with three backticks `.

Why do you think that is wrong? 2147483648 (decimal) is 0x80000000, which looks suspiciously like what you asked for.

Since you still have not shared exactly what devmem2 gives you in both cases I can only guess that devmem2 is failing completely when run in the environment that Qt Creator provides. In this environment it is quite possible sudo will not function.

Wasee

@ChrisW67 thanks;
"sudo devmem2 0x80000000" gives value in terminal is 0x0 but in qt code its value is 2147483648 which I stated above in previous post.
thanks

KroMignon

@Wasee said in Qt program crash why?:

"sudo devmem2 0x80000000" gives value in terminal is 0x0 but in qt code its value is 2147483648 which I stated above in previous post.

I would try to do thing step by step.
First ensure the QProcess call is working, and then try to parse result.
I am not sure that the way you are using QProcess with sudo is the best way.
I would do it this way:

QProcess proc;
QStringList args;

proc.setProcessChannelMode(QProcess::MergedChannels);
args << "devmem2" << "0x80000000";

proc.start("sudo", args);
if(proc.waitForFinished())
{
    QString result = QString(proc.readAll());
    qDebug() << "devmem2 done and returning" << result;
}
else
    qDebug() << "failled to start devmem2";

NOTE: to add code in your post, please use </> button, this made it easier to read

Wasee

@KroMignon thanks for your help:
I coded as you suggested my output is:
devmem2 done and returning: "/dev/mem opened. Memory mapped at address 0xb6f90000. Value at address 0x80000000 (0xb6f90000): 0x0 "
This is very long string I just needed value 0x0 not whole string.

Thanks your help!

jsulm

@Wasee said in Qt program crash why?:

This is very long string I just needed value 0x0 not whole string

Then simply split the string using ':' character and take the second part, see https://doc.qt.io/qt-5/qstring.html#split-5.
This of course assumes that there is only one ':' in the result string. If not, you will need to use split() with regular expression.

KroMignon

@Wasee said in Qt program crash why?:

I coded as you suggested my output is:
devmem2 done and returning: "/dev/mem opened. Memory mapped at address 0xb6f90000. Value at address 0x80000000 (0xb6f90000): 0x0 "
This is very long string I just needed value 0x0 not whole string.
Thanks your help!

That is only a simple string manipulation.
The easiest way is to search for the first occurence of 0x by starting from the end and then parse this string part.
Take a look a QString documentation, you should be able to find this yourself.

Wasee

@KroMignon Hi;
I added following lines in code:

QProcess proc;
QStringList args;

proc.setProcessChannelMode(QProcess::MergedChannels);
args << "devmem2" << "0x80000000";

proc.start("sudo", args);
if(proc.waitForFinished())
{
    QString result = QString(proc.readAll());
    qDebug() << "devmem2 done and returning" << result;
   args = result.split(QRegExp("\\:"));
   args.removeFirst();
 qDebug()<<"Truncated:"<<args;
}
else
    qDebug() << "failled to start devmem2";

Its giving value ("0x0") I need it without bracket 0x0.
Thanks

KroMignon

@Wasee said in Qt program crash why?:

Its giving value ("0x0") I need it without bracket 0x0.
Thanks

Why doing so complicated?
Have your read QString documentation?
You should found QString::lastIndexOf()

QString result = QString(proc.readAll());
QString value =  result.mid(result.lastIndexOf("0x"));
qDebug()<<"Truncated:"<<value;

Wasee

@KroMignon Hi;
Truncated: "0x1
"
Why its not "0x0"? Last quotation mark is on next line.

KroMignon

@Wasee said in Qt program crash why?:

Why its not "0x0"? Last quotation mark is on next line.

perhaps because the return value has changed?
Did you display QProcess output to compare with result?

QString result = QString(proc.readAll());
QString value =  result.mid(result.lastIndexOf("0x"));
qDebug()<<"Returned value:"<<result ;
qDebug()<<"Truncated:"<<value;

Note: it seems that returned string contains also a carriage return byte, you could remove this by using QString::simplified() (cf. https://doc.qt.io/qt-5/qstring.html#simplified)

Wasee

@KroMignon Hi;

qDebug()<<"Returned value:"<<result ;

Returned value:"/dev/mem opened.
Memory mapped at address 0xb6f90000.
Value at address 0x80000000 (0xb6f90000): 0x1
"

thanks

Wasee

Hi everyone;
I code following and getting ASSERT: "count > 0" error. The program has unexpectedly finished. Why?

QProcess proc;
QStringList args;

proc.setProcessChannelMode(QProcess::MergedChannels);
args << "devmem2" << "0x80000000";

proc.start("sudo", args);
if(proc.waitForFinished())
{
    QString result = QString(proc.readAll());
    qDebug() << "devmem2 done and returning" << result;
    QString dds_en = result.mid(result.lastIndexOf("0x"));
    QString test=dds_en.simplified();
    qDebug()<<"Detected:"<<dds_en;
    if(test="0x0"){
    QProcess p1 ;
                    p1.startDetached("/bin/bash", QStringList() << "-c" << "/home/ijaz/bashScripts/script1.sh");
                    QProcess Rx_CF;
                    Rx_CF.start("cat /sys/bus/iio/devices/iio:device1/out_altvoltage0_RX_LO_frequency");
                    Rx_CF.waitForFinished(-1); // will wait forever until finished
                    Rx_CF_read =Rx_CF.readAllStandardOutput();
                     qDebug() << "RX LO"<<Rx_CF_read;
}
                 if(test="0x1"){
                 ac=Rx_CF_read;
                  QFile f("/sys/bus/iio/devices/iio:device1/out_altvoltage1_TX_LO_frequency");
                  if (f.open(QIODevice::WriteOnly))
                  {
                      qint64 count = f.write(ac.toUtf8());
                      Q_ASSERT(count > 0);
                      f.close();
                     qDebug()<<"QFile Run"<<count;
                  }
}

}
else
    qDebug() << "failled to start devmem2";

Thanks

KroMignon

This post is deleted!

Wasee

@KroMignon Hi;
Rx_CF_read and ac are define in header file as QString. Rx_CF_read is RX LO value which is reading from device continuously.
Thanks

jsulm

@Wasee said in Qt program crash why?:

Why?

Ask https://doc.qt.io/qt-5/qfiledevice.html#error

KroMignon

@Wasee said in Qt program crash why?:

Rx_CF_read and ac are define in header file as QString. Rx_CF_read is RX LO value which is reading from device continuously.
Thanks

@Wasee

Are you sure Rx_CF_read contains a valid value?
Why are you using an extra copy to ac?
Are you are writing into a linux virtual file, I don't think it supports UTF-8, but should be latin1.

I would change to code as follow, to understand what's happening:

    if(test=="0x1"){
        QFile f("/sys/bus/iio/devices/iio:device1/out_altvoltage1_TX_LO_frequency");
        qDebug() << "Try to set out_altvoltage1_TX_LO_frequency to" << Rx_CF_read;
        if (f.open(QIODevice::WriteOnly))
        {
            qint64 count = f.write(Rx_CF_read.toLatin1());
            Q_ASSERT(count > 0);
            f.close();
            qDebug()<<"QFile Run"<<count;
        }
    }

EDIT ==> = is to set a value, to compare use ==!!!!
if(test="0x0") ==> if(test=="0x0")
if(test="0x1") ==> if(test=="0x1")

Wasee

@KroMignon Hi;
I change the code but getting ASSERT: "count > 0" error. The program has unexpectedly finished.

Try to set out_altvoltage1_TX_LO_frequency to ""
Thanks

KroMignon

@Wasee said in Qt program crash why?:

Try to set out_altvoltage1_TX_LO_frequency to ""

According to the debug message, you are writing an empty string.
So why should count be greater than 0?

Have you also change the if statements?
if(test="0x1") will change test to "0x1" and not compare test with string "0x1"

In C/C++ the comparison operator is ==

Wasee

@KroMignon Hi;
If statement is working for if(test=="0x0") but not for if(test=="0x1"). Even test value in terminal is "0x1". at this point not entertaining to this if condition.
thanks

JonB

@Wasee
You really need to use a debugger, or even just debug statements, to find out for yourself things like what is in a variable, how should asking here help, other people don't know whether you get 0x0 versus 0x1 or whatever back, you are best placed to discover that....