Null Pointer Exception

[Henning]

Hi,

The Print line throws a NULL Pointer Exception when run!?

Code: Select all

Dim BCnt As Integer
Dim Addr As Integer
Dim RecType As Byte
....
    For x = 0 To LineCount - 1
      BCnt = Val("0x0" & Mid(Buffer[x], 1, 2))
      Addr = Val("0x0" & Mid(Buffer[x], 3, 4))
      RecType = Val("0x0" & Mid(Buffer[x], 7, 2))
      pgmcode = Mid(Buffer[x], 9, Len(Buffer[x]) - 10)
      Print(String(x) & ": " & String(BCnt) & ", " & String(Addr) & ", " & String(RecType) & "\n")
      ....


Have I missed something? Mid to extract a substring is not in the reference???

/Henning

[Henning]

<<If I try to enter it as lower case (mid) it reverts to (Mid) when I leave the line in the editor...

This is a "bug" in the code editor. Will fix this.

There are three Mid

+ Mid assignment as you expect

+ Mid read out

+ and QString . mid (native Qt mid function)

[Slowdown]

Code: Select all

String = Mid(String, StartPos, NumOfChar)

Is the way to go and indeed it's Mid

[Henning]

From the Q7Basic's Language Reference:

Code: Select all

Keyword Mid
Mid(STRINGVARIABLE, Position As Integer, Length As Integer) = {STRINGEXPRESSION | ASCII-Code}

Replaces text inside a string by another text.

Sub Main()
Dim txt As String, replacement As String, originaltxt As String

replacement = "The power of Q7Basic"
originaltxt = "***********************"
Dim i As Integer
For i = 1 To Len(replacement)
Mid(originaltxt, 2, i) = replacement
MsgBox(originaltxt)
Next
End Sub

From the Reference Classes QString:

Code: Select all

Function mid(Position As Integer, N As Integer) As String

Confusing...

And I still don't understand why a NULL Pointer Exception on the line Print( .... ).

/Henning

[Slowdown]

I have used the Function several times but indeed the manual tell's something different.
But the code you posted also works
For replace i use,
Function Replace(Argument As String, Search As String, Replace As String, CaseSensitive As Boolean = True) As String

Replace(...) changes all occurrences of a string inside another string to a new string.

Dim s = "Das ist alles was wir brauchen. Fang nochmal von vorne an."
Dim search = "vorne"
Dim replace = "hinten"
MsgBox(Replace(s, search, replace))

And I still don't understand why a NULL Pointer Exception on the line Print( .... ).

One of the variables has no value you can check this by using stdout.

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Dim MyInt As Integer
MyInt = Null
Print String(MyInt)

Generate the same error you now get.

[Henning]

The problem is converting a Hex String to an Integer.

In VB that is "a piece of cake", Val("&H" & HexString). In Q7b there is no "&H", and Val( "0x0" & HexString) is not functioning... Therefor the integer variable is set to NULL.

HELP!!!

/Henning

[Slowdown]

There is a Function Integer>Hex but no Hex>Integer.
I think that Bernd is that one forgotten.

HELP!!!

to the rescue,

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Event Init()
  MyInt = HexToInt("&h8f")
  MsgBox("Hex to Dec", String(MyInt))
End Event

Function HexToInt(HexValue As String) As Integer
  Dim Lus As Integer
  Dim Power As Integer
  Dim CharValue As String
  Dim Result As Integer

  Result = 0
  HexValue = UCase(Trim(HexValue))
  ' Remove the two left characters &H
  HexValue = Right(HexValue, Len(HexValue) - 2)
  ' now we cycle from right to left taking one character (value) at a time
  For Lus = Len(HexValue) To 1 Step - 1
    Power = Len(HexValue) - Lus
    CharValue = Mid(HexValue, Lus - 1, 1)
    Select Case CharValue
      Case "A"
        CharValue = "10"
      Case "B"
        CharValue = "11"
      Case "C"
        CharValue = "12"
      Case "D"
        CharValue = "13"
      Case "E"
        CharValue = "14"
      Case "F"
        CharValue = "15"
    End Select
    Result = Result +(Integer(CharValue) * CMath.pow(16, Power))
  Next
  Return Result
End Function


Did test some conversions and they worked.

[berndnoetscher]

<<If I try to enter it as lower case (mid) it reverts to (Mid) when I leave the line in the editor...

This is a "bug" in the code editor. Will fix this.

There are three Mid

+ Mid assignment as you expect

+ Mid read out

+ and QString . mid (native Qt mid function)

[berndnoetscher]

<<And I still don't understand why a NULL Pointer Exception on the line Print( .... ).


Printing a Null value is not permitted here. I could change it though. What do you guys think?

[Henning]

The error originates from a Redim Preserve on a Byte Array.

I'm converting an Intel-hex file for an Atmel Mega u-processor programmer to binary to reduce size. It is then used to update firmware in my HW devices over narrowband radio.

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    i = PgmSize Mod 128
    x = PgmSize
    If i <> 0 Then
      i = PgmSize \ 128
      i = i + 1
      PgmSize = i * 128
    End If
    ReDim Preserve PgmBuffer[PgmSize]
'***
    If x <> PgmSize Then
      For i = x + 1 To PgmSize - 1
        PgmBuffer[i] = 255
      Next
    End If
'***


PgmBuffer needs to be exactly a power of 128 bytes.
Before adding the code betwen '***. the expanded part of Byte Array PgmBuffer[] is not by default initialized to a zero (0) value, but Null.
This is ported from VB, there the default value is "0".

Always, if not explicity set, by default initialize numeric variables to a zero value would IMO be prefered. Catching Null's in Print could be useful when testing.

/Henning