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Qt program crash why?



  • Dear all;
    I code following when I called this function in timer event or any other place then my program crashes why?```
    /@
    void secbox::dds_control(){

               QProcess DD;
               DD.start("sudo devmem2 0x80000000");
               DD.waitForFinished(); // will wait forever until finished
              QString dds (DD.readAllStandardOutput());
              dds = dds.replace("(","").replace(")","").replace(":","");
              auto split1 = dds.split("0x");
              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();
                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() << "third arry = " << third_arry ;
    
                    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 ;
                     // //////////////////////////////
                }
    

    @/
    When I run the mu application after running its crashes.
    thanks


  • Lifetime Qt Champion

    @Wasee said in Qt program crash why?:

    running its crashes.

    Use a debugger, see where it crashes, fix it.


  • Moderators

    @Wasee said in Qt program crash why?:
    probably here:

    dds_en.arg(split1.at(1).toLongLong(nullptr,16)).arg(split1.at(2).toLongLong(nullptr,16));

    you do not check the length of the vector before accessing the 2nd and 3rd index of it.

    Don't trust, exercise control !

    [edit: fixed missing word SGaist]



  • @J-Hilk thanks for your reply
    I code following line
    /@
    dds_en =QString::number(split.at(1),16);
    @/
    Its give this error.
    error: no matching function for call to ‘QString::number(const QString&, int)’
    dds_en =QString::number(split.at(1),16);
    ^


  • Lifetime Qt Champion

    Hi,

    Read the documentation of the method. It expects one of C++ numeral types not a QString.



  • 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.


  • Moderators

    @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";
    }
    


  • @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


  • Lifetime Qt Champion

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


  • Moderators

    @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



  • @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";
    }
    @/


  • Moderators

    @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 {



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


  • Lifetime Qt Champion

    I added this but got error expected token ';'

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

    This is a c++17 feature

    Repeating myself...


  • Moderators

    @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.



  • @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....



  • 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;

    @/



  • @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.



  • @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



  • @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



  • @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!


  • Lifetime Qt Champion

    @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.



  • @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.



  • @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



  • @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;
    
    


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



  • @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)



  • @KroMignon Hi;

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

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

    thanks



  • 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



  • This post is deleted!


  • @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


  • Lifetime Qt Champion



  • @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")



  • @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



  • @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 ==



  • @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



  • @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....



  • @Wasee said in Qt program crash why?:

    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

    I don't want to hurt you, but it looks like you are not really understanding what you are doing.
    Why you don't use the debugger to set break points and running this part of code step by step to see what is really happening, as @JonB suggest to you?


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