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Knowledge Base

BUG: All Characters Following CHR(0) are Ignored with MSComm

Article ID: 169502

Article Last Modified on 7/30/1999

APPLIES TO

Microsoft Visual FoxPro 5.0 Standard Edition
Microsoft Visual FoxPro 5.0a

This article was previously published under Q169502

SYMPTOMS

When an instance of the Microsoft Communication Control (MSComm Control) receives a CHR(0) it ignores that character and all characters that follow.

RESOLUTION

One of the following suggestions should resolve this problem:

Set the InputLen property of the Microsoft Communication Control to 1 and read one character at a time.
If possible, do not send CHR(0) or NULL to the Microsoft Communication control.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This has been corrected in Visual FoxPro 6.0.

MORE INFORMATION

The Microsoft Communication Control truncates all characters following, and including, a CHR(0) or NULL that is passed to its Input. This occurs when the "NullDiscard" of the Microsoft Communication control set to ".F."

Steps to Reproduce Behavior

Connect two computers via a NULL Modem cable. For example, COM1 port of a computer (PC1) connected to the COM1 port of another computer (PC2) via a Null Modem Cable.

On PC1, place the following commands into a Visual FoxPro program and then execute it, to create and run a form that sends serial output using the MS Communication Control:

       OUTFORM = CreateObject("comtst1")
       OUTFORM.Show
       READ EVENTS

       DEFINE CLASS COMTST1 AS FORM
         Top = 7
         Left = 88
         Height = 239
         Width = 288
         DOCREATE = .T.
         Caption = "Form1"
         Name = "Form1"
         OUTVAL = .F.
         ADD OBJECT TEXT1 AS TEXTBOX WITH ;
            HEIGHT = 37, ;
            LEFT = 29, ;
            TOP = 84, ;
            WIDTH = 229, ;
            Name = "Text1"
         ADD OBJECT Olecontrol1 AS Olecontrol WITH ;
            OLECLASS="MSCOMMLib.MSComm.1",;
            TOP = 12, ;
            LEFT = 0, ;
            HEIGHT = 100, ;
            WIDTH = 100, ;
            NULLDISCARD = .F., ;
            Name = "Olecontrol1"
         ADD OBJECT Command1 AS CommandBUTTON WITH ;
            TOP = 37, ;
            LEFT = 104, ;
            HEIGHT = 27, ;
            WIDTH = 84, ;
            CAPTION = "Open Port", ;
            TABINDEX = 2, ;
            Name = "Command1"
         ADD OBJECT Command2 AS CommandBUTTON WITH ;
            TOP = 133, ;
            LEFT = 104, ;
            HEIGHT = 27, ;
            WIDTH = 84, ;
            CAPTION = "Send", ;
            Name = "Command2"
         ADD OBJECT Command3 AS CommandBUTTON WITH ;
            TOP = 193, ;
            LEFT = 104, ;
            HEIGHT = 27, ;
            WIDTH = 84, ;
            CAPTION = "Exit", ;
            Name = "Command3"

         PROCEDURE Command1.Click
            IF This.CAPTION="Open Port"
               ThisForm.Olecontrol1.PORTOPEN=.T.
               This.Caption = "Close Port"
            Else
               ThisForm.Olecontrol1.PORTOPEN=.F.
               This.Caption = "Open Port"
            EndIf
         ENDPROC

         PROCEDURE Command2.Click
            *** Send CHR() representation of numbers entered ***
            OVAL1 = ALLTRIM(ThisForm.TEXT1.Value)
            OVAL2 = "chr(" + STRTRAN(OVAL1, " ", ")+chr(") + ")"
            ThisForm.Olecontrol1.OUTPUT=&OVAL2
         ENDPROC

         PROCEDURE Command3.Click
            ThisForm.Release
            CLEAR EVENTS
         ENDPROC

       ENDDEFINE

Switch to PC2 and place the following code into a Visual FoxPro program and execute it to create and run a form that receives serial input using the MS Communication Control:

       INFORM = CREATEOBJECT("comtst2")
       INFORM.SHOW
       READ EVENTS

       DEFINE CLASS comtst2 AS FORM
           Top = 5
           Left = 1
           Height = 216
           Width = 410
           DoCreate = .T.
           Caption = "Form1"
           Name = "Form1"
           inval1 = .F.
           inval2 = .F.
           ADD OBJECT Olecontrol1 AS OleCONTROL WITH ;
               OleCLASS="MSCOMMLib.MSComm.1",;
               TOP = 12, ;
               LEFT = 12, ;
               HEIGHT = 100, ;
               WIDTH = 100, ;
               NAME = "Olecontrol1", ;
               NullDiscard = .F., ;
               RThreshold = 10
           ADD OBJECT Command1 AS CommandBUTTON WITH ;
               TOP = 24, ;
               LEFT = 150, ;
               HEIGHT = 27, ;
               WIDTH = 84, ;
               CAPTION = "Open Port", ;
               NAME = "Command1"
           ADD OBJECT Edit1 AS EditBOX WITH ;
               FONTNAME = "Arial", ;
               HEIGHT = 64, ;
               LEFT = 24, ;
               TOP = 72, ;
               WIDTH = 252, ;
               NAME = "Edit1"
           ADD OBJECT Command2 AS CommandBUTTON WITH ;
               TOP = 108, ;
               LEFT = 298, ;
               HEIGHT = 27, ;
               WIDTH = 84, ;
               CAPTION = "Clear Text", ;
               NAME = "Command2"
           ADD OBJECT Command3 AS CommandBUTTON WITH ;
               TOP = 72, ;
               LEFT = 298, ;
               HEIGHT = 27, ;
               WIDTH = 84, ;
               CAPTION = "View Input", ;
               ENABLED = .F., ;
               NAME = "Command3"
           ADD OBJECT Command4 AS CommandBUTTON WITH ;
               TOP = 178, ;
               LEFT = 150, ;
               HEIGHT = 27, ;
               WIDTH = 84, ;
               CAPTION = "Exit", ;
               NAME = "Command4"

           PROCEDURE Command1.CLICK
               IF This.CAPTION="Open Port"
                   ThisForm.Olecontrol1.portopen=.T.
                   This.CAPTION = "Close Port"
                   ThisForm.Command3.ENABLED=.T.
               ELSE
                   ThisForm.Olecontrol1.portopen=.F.
                   This.CAPTION = "Open Port"
                   ThisForm.Command3.ENABLED=.F.
               ENDIF
           ENDPROC

           PROCEDURE Command2.CLICK
               ThisForm.Edit1.VALUE = ""
           ENDPROC

           PROCEDURE Command3.CLICK
               ThisForm.inval1 = ThisForm.Olecontrol1.INPUT
               FOR i = 1 TO LEN(ThisForm.inval1)
                   ThisForm.inval2 = ASC(SUBSTR(ThisForm.inval1, i, 1))
                   ThisForm.Edit1.VALUE=ThisForm.Edit1.VALUE+;
                           " "+ALLTRIM(STR(ThisForm.inval2))+" "
               ENDFOR
           ENDPROC

           PROCEDURE Command4.CLICK
               ThisForm.RELEASE
               CLEAR EVENTS
           ENDPROC

       ENDDEFINE

Click Open Port on the InForm form on PC2 to open the communication port on that computer.
Switch to PC1 and click Open Port on the OutForm form on PC1 to open the communication port on that computer.
Select the edit box on OutForm and enter the following numbers into the first line:
```
      15 255 13 10 25
                                
```
NOTE: Ensure that the numbers are entered with a space between them but with no space before the first (15) and after the last number (25).
Click SEND on OutForm to send the numbers.
Switch to PC2 and click View Input on InForm. Look at the contents of the edit box.

NOTE: The characters sent by OutForm are displayed in the edit box of InForm. So, the characters are being received and recognized by MS Communication Control on the receiving end.
Click Clear Text to clear the edit box.
Go back to PC1 and insert a "0" between the second and third number in the edit box of OutForm so that the entries look like the following:
```
       15 255 0 13 10 25
                                
```
Click SEND on OutForm to send the numbers.
Switch to PC1 and click View Input. Look at the contents of the edit box.

NOTE: Only the first and the second numbers (15 255), sent by OutForm on PC1, are displayed in the edit box of InForm. The "0" and the numbers following it are not displayed. This illustrates that after a receiving CHR(0) or NULL that the MS Communication Control ignores that particular character and all characters following it.

Keywords: kbbug kbfix kbinterop kbcode KB169502

Microsoft KB Archive/169502

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