Why No BinaryStream.WriteCstring or ReadCString?

There are MemoryBlock.CString(offset) setter and getter methods, but why are there no BinaryStream.ReadCstring and WriteCString methods? Was it an oversight or is there a reason for not having them? If there is no reason not to have them I’ll put in a feature request

Writing an Extends method for BinaryStream.WriteCstring method is simple and would be consistent with the rest of the API (Just write the string and then a Null byte)… But doing ReadCString as an extends would mean (as far as I can see) doing something like read the stream byte by byte until i find a 0 (or reach the end of the MB) - which could be slow…

The better way would likely be to work with the memoryblock and do something like:

Dim S as string = MB.CString(Stream.Position) Stream.Postion = Stream.Postion + S.LenB + 1
So I can’t extend BinaryStream unless I also pass in the memoryblock… doable but not consistent with the API…

It really feels like this capability should be built in!

  • Karen

Submitted a feature request:

feedback://showreport?report_id=56095

Cstrings were never meant for general use. They’re really only there for use with declares.

Is not the same true for PStrings for which there are BinaryStream methods?

CStrings are useful for compact binary data formats… else one needs either to use fixed string sizes (padded with nulls when needed) or write longer strings analogously to PStrings where one uses more than 1 byte for string length.

Initially I was writing code to do the latter. but as i’m trying to be as compact as possible, I realized Cstrings only have 1byte overhead regardless of size- though I suspect with the penalty of more CPU usage for reading. I was surprised to find those methods were missing!

Anyway in the spirit consistency and completeness please consider adding those methods as they really are useful for things beyond declares.

  • Karen

to write long PStrings, I ended up with this :

[code]Public Sub WriteString(extends bs As BinaryStream, s As String)
If s.LenB<256 Then
bs.WriteUInt8(1)
bs.WriteUInt8(1)
bs.WritePString(s)
Elseif s.LenB<65536 Then
bs.WriteUInt8(1)
bs.WriteUInt8(2)
bs.WriteUInt16(s.LenB)
bs.Write(s)
Else
bs.WriteUInt8(1)
bs.WriteUInt8(4)
bs.WriteUInt32(s.LenB)
bs.Write(s)
End If

End Sub
[/code]

and this

[code]Public Function ReadString(extends bs as BinaryStream, Enc as TextEncoding = nil) as String
Dim detector As UInt8 = bs.ReadUInt8

If detector=1 Then
Dim psize As UInt8 = bs.ReadUInt8

If psize>0 Then
  Select Case psize
  Case 1
    ' standard 8 bits pstring
    Return bs.ReadPString( Enc)
  Case 2
    Dim size As UInt16 = bs.ReadUInt16
    Return bs.Read(size, Enc).DefineEncoding(Encodings.UTF8)
  Case 4
    Dim size As UInt32 = bs.ReadUInt32
    Return bs.Read(size, Enc).DefineEncoding(Encodings.UTF8)
  Else
    ' still original 8bits pstring
    bs.Position = bs.Position-2
    Return bs.ReadPString( Enc)
  End Select
Else
  Return ""
End If

Else
’ standard 8 bits pstring
bs.Position = bs.Position-1
Return bs.ReadPString( Enc)
End If

End Function
[/code]

[quote=441796:@Karen Atkocius]Is not the same true for PStrings for which there are BinaryStream methods?
[/quote]
CString, PString, WString and some others leaked out from being only available for declares years ago (pre-2008 ish)

As for writing compact binary formats the IDE does that with binary projects and doesnt need or use CStrings
It basically uses a lengtn/data format like Jean-Yves describes

For a CString something, whether its your code or framework code, has to read byte by byte until it hits the NUL byte

[quote=441858:@Norman Palardy]
As for writing compact binary formats the IDE does that with binary projects and doesnt need or use CStrings
It basically uses a lengtn/data format like Jean-Yves describes

For a CString something, whether its your code or framework code, has to read byte by byte until it hits the NUL byte[/quote]

As I said, the approach I originally took was including the length information… The tradeoff between the 2 approaches is processing speed vs compactness… which is more important (and if the difference is significant) depends on specific usage.

BTW I would think the framework code would be faster at finding the Nul byte than my code could be.

  • karen

[quote=441806:@Jean-Yves Pochez]to write long PStrings, I ended up with this :
[/quote]

That got me thinking… This code is meant to serialize generic recordsSets which could have a lot records and a lot of fields. Most text strings used as IDs or for descriptions in table fields tend to be shorter than 255 characters, so maybe this would be a little more efficient if a bit less elegant:

[code]Public Sub WriteString(extends bs As BinaryStream, s As String)
Const Bit8 = 253
Const Bit16 = 254
Const Bit32 = 255

Select Case S.LenB
Case Is < Bit8
bs.WritePString S

Case Is < 256
bs.WriteUInt8 Bit8
bs.Write S

Case Is <65536 Then
bs.WriteUInt8 Bit16
bs.Write S

Else
bs.WriteUInt8 Bit32
bs.Write(s)
End Select

End Sub
[/code]

and this

[code]Public Function ReadString(extends bs as BinaryStream, Enc as TextEncoding = nil) as String

Const Bit8 = 253
Const Bit16 = 254
Const Bit32 = 255

Select case bs.ReadUInt8
Case Is < Bit8
Return bs.ReadPString(Enc)
Case Bit8
Return bs.Read(bs.readUint8, Enc)
Case Bit16
Return bs.Read(bs.readUint16, Enc)
Else
Return bs.Read(bs.readUint32, Enc)
End If
End Function
[/code]

its still much the same loop in the framework or your code

dim buffer as string
while binarystream.eof = false
    dim c as Uint8 = binarystream.readUint8
    if c <> 0 then
        buffer = buffer + chrb(c)
   end if
wend

return buffer

Oops that should have been:

[code]Public Sub WriteString(extends bs As BinaryStream, s As String)
Const Bit8 = 253
Const Bit16 = 254
Const Bit32 = 255

Select Case S.LenB
Case Is < Bit8
bs.WritePString S

Case Is < 256
bs.WriteUInt8 Bit8
bs.WritePString S

Case Is <65536 Then
bs.WriteUInt8 Bit16
bs.WriteUInt16 S.LenB
bs.Write S

Else
bs.WriteUInt8 Bit32
bs.WriteUInt32 S.LenB
bs.Write(s)
End Select

End Sub
[/code]

and this

[code]Public Function ReadString(extends bs as BinaryStream, Enc as TextEncoding = nil) as String

Const Bit8 = 253
Const Bit16 = 254
Const Bit32 = 255

Select case bs.ReadUInt8
Case Is < Bit8
bs.Position = bs.position -1
Return bs.ReadPString(Enc)
Case Bit8
Return bs.Read(bs.readUint8, Enc)
Case Bit16
Return bs.Read(bs.readUint16, Enc)
Else
Return bs.Read(bs.readUint32, Enc)
End If
End Function
[/code]

This implementation saves one byte per string for strings > 255 characters