System.NullReferenceException , why?

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  • Alex J.
    #1

    System.NullReferenceException , why?

    I just started to learn C# (my background is in C++), and right now I
    study the sockets, TCP/IP etc... so, I found a usefull source code at:
    http://www.codeguru.com/Csharp/Cshar...cle.php/c8781/.
    But there is a scenarion that throw a strange exception. So, the client
    is connected to the server, I send a message from client to server and
    viceversa and than I stop the server from the 'x' button from the right-up
    corner; in that moment the client throw System.NullRefe renceException:

    An unhandled exception of type 'System.NullRef erenceException ' occurred
    in system.dll
    Additional information: Object reference not set to an instance of an
    object.

    the cursor is placed here:
    000000a0 0F B6 F0 movzx esi,al

    and the Call Stack stopped here:
    system.dll!Syst em.Net.Sockets. OverlappedAsync Result.Completi onPortCallback( uint
    errorCode = 64, uint numBytes = 0, System.Threadin g.NativeOverlap ped*
    nativeOverlappe d = 1750608) + 0xa0 bytes

    There is a solution?

    Thank you in advance.

    ..:Alex:.


    Tags: None
    • Ignacio Machin \( .NET/ C# MVP \)
      #2
      Re: System.NullRefe renceException , why?

      Hi,

      What escenrio?

      What is the code you were executing when this exception is thrown

      That exception happen when you are access a variable that is null


      --
      Ignacio Machin,
      ignacio.machin AT dot.state.fl.us
      Florida Department Of Transportation

      "Alex J." <alex_77ro@yaho o.com> wrote in message
      news:%232FjcTWO GHA.2300@TK2MSF TNGP15.phx.gbl. ..[color=blue]
      > I just started to learn C# (my background is in C++), and right now I
      > study the sockets, TCP/IP etc... so, I found a usefull source code at:
      > http://www.codeguru.com/Csharp/Cshar...cle.php/c8781/.
      > But there is a scenarion that throw a strange exception. So, the
      > client is connected to the server, I send a message from client to server
      > and viceversa and than I stop the server from the 'x' button from the
      > right-up corner; in that moment the client throw
      > System.NullRefe renceException:
      >
      > An unhandled exception of type 'System.NullRef erenceException ' occurred
      > in system.dll
      > Additional information: Object reference not set to an instance of an
      > object.
      >
      > the cursor is placed here:
      > 000000a0 0F B6 F0 movzx esi,al
      >
      > and the Call Stack stopped here:
      >
      > system.dll!Syst em.Net.Sockets. OverlappedAsync Result.Completi onPortCallback( uint
      > errorCode = 64, uint numBytes = 0, System.Threadin g.NativeOverlap ped*
      > nativeOverlappe d = 1750608) + 0xa0 bytes
      >
      > There is a solution?
      >
      > Thank you in advance.
      >
      > .:Alex:.
      >[/color]


        Comment

        • Alex J.
          #3
          Re: System.NullRefe renceException , why?

          Hi,

          I don't know if you took a look at the source code from this url:
          http://www.codeguru.com/Csharp/Cshar...cle.php/c8781/
          Try to make 2 projects from these files a client and a server. 'Start
          Listen' the server and then connect the client to the server. Kill the
          server from procesess (task manager).
          You will se how the client throw the exeption in subject:
          System.NullRefe renceException

          Let me know if you understand me.

          Thank you for your attention.

          ..:Alex:.


          "Ignacio Machin ( .NET/ C# MVP )" <ignacio.mach in AT dot.state.fl.us > wrote
          in message news:OS7OEEXOGH A.2992@tk2msftn gp13.phx.gbl...[color=blue]
          > Hi,
          >
          > What escenrio?
          >
          > What is the code you were executing when this exception is thrown
          >
          > That exception happen when you are access a variable that is null
          >
          >
          > --
          > Ignacio Machin,
          > ignacio.machin AT dot.state.fl.us
          > Florida Department Of Transportation
          >
          > "Alex J." <alex_77ro@yaho o.com> wrote in message
          > news:%232FjcTWO GHA.2300@TK2MSF TNGP15.phx.gbl. ..[color=green]
          >> I just started to learn C# (my background is in C++), and right now I
          >> study the sockets, TCP/IP etc... so, I found a usefull source code at:
          >> http://www.codeguru.com/Csharp/Cshar...cle.php/c8781/.
          >> But there is a scenarion that throw a strange exception. So, the
          >> client is connected to the server, I send a message from client to server
          >> and viceversa and than I stop the server from the 'x' button from the
          >> right-up corner; in that moment the client throw
          >> System.NullRefe renceException:
          >>
          >> An unhandled exception of type 'System.NullRef erenceException '
          >> occurred in system.dll
          >> Additional information: Object reference not set to an instance of an
          >> object.
          >>
          >> the cursor is placed here:
          >> 000000a0 0F B6 F0 movzx esi,al
          >>
          >> and the Call Stack stopped here:
          >>
          >> system.dll!Syst em.Net.Sockets. OverlappedAsync Result.Completi onPortCallback( uint
          >> errorCode = 64, uint numBytes = 0, System.Threadin g.NativeOverlap ped*
          >> nativeOverlappe d = 1750608) + 0xa0 bytes
          >>
          >> There is a solution?
          >>
          >> Thank you in advance.
          >>
          >> .:Alex:.
          >>[/color]
          >
          >[/color]


            Comment

            • Alex J.
              #4
              Re: System.NullRefe renceException , why?

              > That exception happen when you are access a variable that is null

              ok, d'accord :), but where exactly it happens in that code?
              Do you have a ideea?


              "Ignacio Machin ( .NET/ C# MVP )" <ignacio.mach in AT dot.state.fl.us > wrote
              in message news:OS7OEEXOGH A.2992@tk2msftn gp13.phx.gbl...[color=blue]
              > Hi,
              >
              > What escenrio?
              >
              > What is the code you were executing when this exception is thrown
              >
              > That exception happen when you are access a variable that is null
              >
              >
              > --
              > Ignacio Machin,
              > ignacio.machin AT dot.state.fl.us
              > Florida Department Of Transportation
              >
              > "Alex J." <alex_77ro@yaho o.com> wrote in message
              > news:%232FjcTWO GHA.2300@TK2MSF TNGP15.phx.gbl. ..[color=green]
              >> I just started to learn C# (my background is in C++), and right now I
              >> study the sockets, TCP/IP etc... so, I found a usefull source code at:
              >> http://www.codeguru.com/Csharp/Cshar...cle.php/c8781/.
              >> But there is a scenarion that throw a strange exception. So, the
              >> client is connected to the server, I send a message from client to server
              >> and viceversa and than I stop the server from the 'x' button from the
              >> right-up corner; in that moment the client throw
              >> System.NullRefe renceException:
              >>
              >> An unhandled exception of type 'System.NullRef erenceException '
              >> occurred in system.dll
              >> Additional information: Object reference not set to an instance of an
              >> object.
              >>
              >> the cursor is placed here:
              >> 000000a0 0F B6 F0 movzx esi,al
              >>
              >> and the Call Stack stopped here:
              >>
              >> system.dll!Syst em.Net.Sockets. OverlappedAsync Result.Completi onPortCallback( uint
              >> errorCode = 64, uint numBytes = 0, System.Threadin g.NativeOverlap ped*
              >> nativeOverlappe d = 1750608) + 0xa0 bytes
              >>
              >> There is a solution?
              >>
              >> Thank you in advance.
              >>
              >> .:Alex:.
              >>[/color]
              >
              >[/color]


                Comment

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