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local string always corrupt

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  • J jsulm
    22 Oct 2018, 06:04

    @rohit713 As @Christian-Ehrlicher said: you implemented a nice example for stack overflow :-)
    You should use strncpy.

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    rohit713
    wrote on 22 Oct 2018, 06:07 last edited by
    #13

    @jsulm i also tried strncpy but the same problem occurs .

    J 1 Reply Last reply 22 Oct 2018, 06:07
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    • R rohit713
      22 Oct 2018, 06:07

      @jsulm i also tried strncpy but the same problem occurs .

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      jsulm
      Lifetime Qt Champion
      wrote on 22 Oct 2018, 06:07 last edited by
      #14

      @rohit713 Can you show how you used strncpy?

      https://forum.qt.io/topic/113070/qt-code-of-conduct

      R 2 Replies Last reply 22 Oct 2018, 06:12
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      • J jsulm
        22 Oct 2018, 06:07

        @rohit713 Can you show how you used strncpy?

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        rohit713
        wrote on 22 Oct 2018, 06:12 last edited by
        #15
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        • J jsulm
          22 Oct 2018, 06:07

          @rohit713 Can you show how you used strncpy?

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          rohit713
          wrote on 22 Oct 2018, 06:13 last edited by rohit713
          #16

          @jsulm strncpy(pr,ijl.toLocal8Bit().data(),ijl.length());

          J A 2 Replies Last reply 22 Oct 2018, 06:16
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          • R rohit713
            22 Oct 2018, 06:13

            @jsulm strncpy(pr,ijl.toLocal8Bit().data(),ijl.length());

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            jsulm
            Lifetime Qt Champion
            wrote on 22 Oct 2018, 06:16 last edited by
            #17

            @rohit713 This is same stack overflow as before...

            https://forum.qt.io/topic/113070/qt-code-of-conduct

            R 1 Reply Last reply 22 Oct 2018, 06:16
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            • J jsulm
              22 Oct 2018, 06:16

              @rohit713 This is same stack overflow as before...

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              rohit713
              wrote on 22 Oct 2018, 06:16 last edited by rohit713
              #18

              @jsulm can u share the stack overflow link

              J A 2 Replies Last reply 22 Oct 2018, 06:17
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              • R rohit713
                22 Oct 2018, 06:16

                @jsulm can u share the stack overflow link

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                jsulm
                Lifetime Qt Champion
                wrote on 22 Oct 2018, 06:17 last edited by
                #19

                @rohit713 What link? Think about what will happen if ijl.toLocal8Bit().data() is longer than pr.

                https://forum.qt.io/topic/113070/qt-code-of-conduct

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                • R rohit713
                  22 Oct 2018, 06:13

                  @jsulm strncpy(pr,ijl.toLocal8Bit().data(),ijl.length());

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                  aha_1980
                  Lifetime Qt Champion
                  wrote on 22 Oct 2018, 06:17 last edited by
                  #20

                  @rohit713

                  Use qstrncpy(pr, ijl.toLocal8Bit().constData(),sizeof(pr));

                  Qt has to stay free or it will die.

                  R 1 Reply Last reply 22 Oct 2018, 06:24
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                  • A aha_1980
                    22 Oct 2018, 06:17

                    @rohit713

                    Use qstrncpy(pr, ijl.toLocal8Bit().constData(),sizeof(pr));

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                    rohit713
                    wrote on 22 Oct 2018, 06:24 last edited by
                    #21

                    @aha_1980 same problem occur with qstrncpy.

                    J 1 Reply Last reply 22 Oct 2018, 06:43
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                    • R rohit713
                      22 Oct 2018, 06:24

                      @aha_1980 same problem occur with qstrncpy.

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                      jsulm
                      Lifetime Qt Champion
                      wrote on 22 Oct 2018, 06:43 last edited by
                      #22

                      @rohit713 So, you used exactly this line:

                      qstrncpy(pr, ijl.toLocal8Bit().constData(),sizeof(pr));
                      

                      ?
                      Use debugger and step by step execution to see what happens.

                      https://forum.qt.io/topic/113070/qt-code-of-conduct

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                      • R rohit713
                        22 Oct 2018, 06:16

                        @jsulm can u share the stack overflow link

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                        ambershark
                        wrote on 24 Oct 2018, 04:47 last edited by ambershark
                        #23

                        @rohit713 said in local string always corrupt:

                        @jsulm can u share the stack overflow link

                        Lol he means an actual stack overflow, i.e. you have the potential for overrunning the memory in your buffer with how you used strcpy and strncpy. Not stackoverflow.com the website. ;)

                        You also don't leave room for the null terminator (or copy it). So you're resulting string if used in any string function is almost guaranteed to crash, at least in release mode. I don't think either of these are your actual issue though.

                        before strcpy it contain "risk" after calling strcpy it gives not accesible.

                        What does that mean? What gives not accessible? The debugger? If it was truly not accessible then it would cause a crash. After it's "not accessible" can you output it via qdebug? My guess here is QString is just reallocating it's internal memory and you are now watching the wrong memory location.

                        If you could show us the backtrace from the crash log that would help. Like I said I tested the code and it worked. I realize Qt5 is different that 4, but that string memory should be good during your copy even in Qt4. It worked in 5 I suspect if I had easy access to Qt4 it would work there too. Can you give us more information on what the actual problem is? "Not accessible" doesn't mean much.

                        My L-GPL'd C++ Logger github.com/ambershark-mike/sharklog

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