Qt program crash why?

ChrisW67

Further to @J.Hilk's suggestion, it would fail here because either the output of devmem2 was not as expected, or because it failed outright (as it does on my machine).

Assuming devmem2 works at all, you are expecting something like this on stdout:

/dev/mem opened.
Memory mapped at address 0x7f5c34dc3000.
Value at address 0x0 0x7f5c34dc3000 0xF000EEF3

This is what your split1 array looks like:

(
"/dev/mem opened.\nMemory mapped at address ", 
"7f5c34dc3000.\nValue at address ", 
"0 ", 
"7f5c34dc3000 ", 
"F000EEF3\n"
)

So, split1 is not what you are expecting and one or both attempts to convert toLongLong() is probably failing. What you do with that information later is not what you expect.

If devmem2 fails completely then the split1 array contains only a single entry and the split.at() calls seg fault.

J.Hilk

@Wasee
you need to check the length of your split vector, I don't see that run your corrected code ?

if(auto split1 = dds.split("0x"); split1.size() >3) {
    //your code
    QString dds_en("%1:%2");
              dds_en = dds_en.arg(split1.at(1).toLongLong(nullptr,16)).arg(split1.at(2).toLongLong(nullptr,16));
              //str2 =QString::number(split1.at(2),16);
                   qDebug()<<"Detected:"<<dds_en;
                dds_control();
} else {
    qDebug() << "String was not the expected format/length";
}

Wasee

@J-Hilk I run the above code it giving me error at this line.

if(auto split1 = dds.split("0x") && split1.size() >3)

use of split1 before deduction

I remove your ; between your code lines giving error expected token ';' then I replace it with "&&"
thanks

Christian Ehrlicher

@Wasee This is a c++17 feature - either enable c++17 or write move auto split1 = dds.split("0x") outside the if statement.

J.Hilk

@Wasee

if(auto split1 = dds.split("0x"); split1.size() >3) {

is most definitely the correct syntax, I even test compiled a small minimal example.

can you post what you actually wrote ? and what version of c++ did you set? the init statement is a c++17 feature. If you're using an older version, you have to move that before the if case

Wasee

@J-Hilk Hi;
/@

           QProcess DD;
           DD.start("sudo devmem2 0x80000000");
           DD.waitForFinished(); // will wait forever until finished
          QString dds (DD.readAllStandardOutput());
          dds = dds.replace("(","").replace(")","").replace(":","");

        if( ( auto split1 = dds.split("0x"); split1.size()>3{
            if(dds_en=="0:0"){
                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();
                //QString ac = Rx_CF_read;
            }
            else{
                 ac = Rx_CF_read;
                QString ab="cd /sys/bus/iio/devices/iio\:device1 && echo";
                //QString ac=ui->CF_new->text();

                qDebug() << "Tx_LO Tunned ON= " << ac ;

                QString ad = " > out_altvoltage1_TX_LO_frequency";
                             ab.append(ac) ;
                QProcess band1_on;
                //  band1_on.start(band1_1.append(third_arry));
                 band1_on.start(ab.append(ad));
                 band1_on.waitForFinished(-1); //
                  qDebug() << "band1_on  = " << ab ;
                 // //////////////////////////////
          QString dds_en("%1:%2");
         // dds_en = dds_en.arg(split.at(1).toLongLong(nullptr,16)).arg(split.at(2).toLongLong(nullptr,16));
          dds_en =QString::number(split.at(1),16);
               qDebug()<<"Detected:"<<dds_en;
           // dds_control();

}
} else{
qDebug() << "String was not the expected format/length";
}
@/

J.Hilk

@Wasee said in Qt program crash why?:

if( ( auto split1 = dds.split("0x"); split1.size()>3{

remove one of the opening ( and add the missing closing ) before the {

Wasee

@J-Hilk Hi;
I added this but got error expected token ';'
if( auto split1 = dds.split("0x"); split1.size()>3){
//my code
}

Christian Ehrlicher

I added this but got error expected token ';'

@Christian-Ehrlicher said in Qt program crash why?:

This is a c++17 feature

Repeating myself...

J.Hilk

@Christian-Ehrlicher
its the wrong error message for that, it should be
language feature 'init-statements in if/switch' requires compiler flag '/std:c++17'

the missing ; is somewhere else in the ops code.

JonB

@Wasee said in Qt program crash why?:

if( ( auto split1 = dds.split("0x"); ...

The doubled (s are wrong, and the cause of the error message. I think @J-Hilk has already pointed this out earlier....

Wasee

Hi everyone when I run this code I am getting the value of Detected "0:2147483648" which is wrong in terminal I am getting value 0x0 which is correct why wrong in qtcreator?
/@
QProcess DD;
DD.start("sudo devmem2 0x80000000");
DD.waitForFinished(); // will wait forever until finished
QString dds (DD.readAllStandardOutput());
dds = dds.replace("(","").replace(")","").replace(":","");
auto split = dds.split("0x");
QString dds_en("%1:%2");
dds_en = dds_en.arg(split.at(1).toLongLong(nullptr,16)).arg(split.at(2).toLongLong(nullptr,16));
// dds_en =QString::number(split.at(1),16);
qDebug()<<"Detected:"<<dds_en;

@/

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;