Using + or & for concatenating strings - and an implicit cast

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  • FB's .NET Dev PC
    #1

    Using + or & for concatenating strings - and an implicit cast

    Interesting note, the code below as is will attempt to cast what is clearly
    indicated as a string into a double. This is becuase the use of + as a
    concatenation operator. The error message generated is included with the
    code. Use & instead and it works.



    Dim pstrSend As String = ""

    'ActionCode 1 and 2 are type BYTE, Msg is a byVal string parameter



    pstrSend = Chr(ActionCode1 ) + Chr(ActionCode2 ) + Msg + &HFF & vbCr

    'write and flush

    objSocketWriter .Write(pstrSend )

    objSocketWriter .Flush()

    End Function



    An unhandled exception of type 'System.Invalid CastException' occurred in
    microsoft.visua lbasic.dll

    Additional information: Cast from string "cThis is a longer test message" to
    type 'Double' is not valid.



    System.InvalidC astException: Cast from string "cThis is a longer test
    message" to type 'Double' is not valid. ---> System.FormatEx ception: Input
    string was not in a correct format.




    Tags: None
    • One Handed Man \( OHM - Terry Burns \)
      #2
      Re: Using + or & for concatenating strings - and an implicit cast

      Now try it with OPTION Strict = ON and see if it compiles

      --
      OHM ( Terry Burns ) * Use the following to email me *

      Dim ch() As Char = "ufssz/cvsotAhsfbuTpmv ujpotXjui/OFU".ToCharArra y()
      For i As Int32 = 0 To ch.Length - 1
      ch(i) = Convert.ToChar( Convert.ToInt16 (ch(i)) - 1)
      Next
      Process.Start(" mailto:" & New String(ch))
      --


      "FB's .NET Dev PC" <chipmonk3775@h otmail.com> wrote in message
      news:uy9bJq6rEH A.2136@TK2MSFTN GP14.phx.gbl...[color=blue]
      > Interesting note, the code below as is will attempt to cast what is
      > clearly indicated as a string into a double. This is becuase the use of +
      > as a concatenation operator. The error message generated is included with
      > the code. Use & instead and it works.
      >
      >
      >
      > Dim pstrSend As String = ""
      >
      > 'ActionCode 1 and 2 are type BYTE, Msg is a byVal string parameter
      >
      >
      >
      > pstrSend = Chr(ActionCode1 ) + Chr(ActionCode2 ) + Msg + &HFF & vbCr
      >
      > 'write and flush
      >
      > objSocketWriter .Write(pstrSend )
      >
      > objSocketWriter .Flush()
      >
      > End Function
      >
      >
      >
      > An unhandled exception of type 'System.Invalid CastException' occurred in
      > microsoft.visua lbasic.dll
      >
      > Additional information: Cast from string "cThis is a longer test message"
      > to type 'Double' is not valid.
      >
      >
      >
      > System.InvalidC astException: Cast from string "cThis is a longer test
      > message" to type 'Double' is not valid. ---> System.FormatEx ception: Input
      > string was not in a correct format.
      >
      >
      >
      >[/color]


        Comment

        • Jay B. Harlow [MVP - Outlook]
          #3
          Re: Using + or &amp; for concatenating strings - and an implicit cast

          FB,[color=blue]
          > pstrSend = Chr(ActionCode1 ) + Chr(ActionCode2 ) + Msg + &HFF & vbCr[/color]
          &HFF is an "number", Msg needs to be converted to a number so that the two
          numbers can be added together.

          Which is why I use & for concatenating strings, the only implicit
          conversions are to string.

          Also if you use Option Strict On, you will get a compile error instead of a
          runtime error.

          Hope this helps
          Jay

          "FB's .NET Dev PC" <chipmonk3775@h otmail.com> wrote in message
          news:uy9bJq6rEH A.2136@TK2MSFTN GP14.phx.gbl...[color=blue]
          > Interesting note, the code below as is will attempt to cast what is
          > clearly indicated as a string into a double. This is becuase the use of +
          > as a concatenation operator. The error message generated is included with
          > the code. Use & instead and it works.
          >
          >
          >
          > Dim pstrSend As String = ""
          >
          > 'ActionCode 1 and 2 are type BYTE, Msg is a byVal string parameter
          >
          >
          >
          > pstrSend = Chr(ActionCode1 ) + Chr(ActionCode2 ) + Msg + &HFF & vbCr
          >
          > 'write and flush
          >
          > objSocketWriter .Write(pstrSend )
          >
          > objSocketWriter .Flush()
          >
          > End Function
          >
          >
          >
          > An unhandled exception of type 'System.Invalid CastException' occurred in
          > microsoft.visua lbasic.dll
          >
          > Additional information: Cast from string "cThis is a longer test message"
          > to type 'Double' is not valid.
          >
          >
          >
          > System.InvalidC astException: Cast from string "cThis is a longer test
          > message" to type 'Double' is not valid. ---> System.FormatEx ception: Input
          > string was not in a correct format.
          >
          >
          >
          >[/color]


            Comment

            • Cor Ligthert
              #4
              Re: Using + or &amp; for concatenating strings - and an implicit cast

              Yes


                Comment

                • Herfried K. Wagner [MVP]
                  #5
                  Re: Using + or &amp; for concatenating strings - and an implicit cast

                  "FB's .NET Dev PC" <chipmonk3775@h otmail.com> schrieb:[color=blue]
                  > Interesting note, the code below as is will attempt to cast what is
                  > clearly indicated as a string into a double. This is becuase the use of +
                  > as a concatenation operator. The error message generated is included with
                  > the code. Use & instead and it works.[/color]

                  Add 'Option Strict On' on top of your source file and "try again".

                  --
                  Herfried K. Wagner [MVP]
                  <URL:http://dotnet.mvps.org/>

                    Comment

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