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Q105010: How To Use the OpenComm() Function with FOXTOOLS.FLL

Article: Q105010
Product(s): Microsoft FoxPro
Version(s): 2.50 2.50a 2.50b 2.60 2.60a
Operating System(s): 
Keyword(s): kbcode
Last Modified: 11-AUG-1999

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft FoxPro for Windows, versions 2.5, 2.5a, 2.5b, 2.6, 2.6a 
-------------------------------------------------------------------------------

SUMMARY
=======

OpenComm() is a function that can be called using FOXTOOLS.FLL to open the COM
or LPT ports. Below is a complete description of OpenComm().

MORE INFORMATION
================

Purpose
-------

The OpenComm() function opens a communications device.

Function Syntax
---------------

  OpenComm(<port>, <in_q>, <out_q>)

  Argument       Description
  -----------------------------------------------------------------

  <port>         Points to a null-terminated string that specifies
                 the device in the form COM<n> or LPT<n>, where <n>
                 is the device number.

  <in_q>         Specifies the size, in bytes, of the receiving
                 queue. This parameter is ignored for LPT devices.

  <out_q>        Specifies the size, in bytes, of the transmission
                 queue. This parameter is ignored for LPT devices.

Returns
-------

The return value identifies the open device if the function is successful.
Otherwise, it is less than zero.

Errors
------

If the function fails, it may return one of the following error values:

  Value     Meaning
  --------------------------------------------------------------------

  -12       The device's baud rate is unsupported.
  -11       The specified byte size is invalid.
  -10       The hardware is not available (is locked by another device).
   -5       The default parameters are in error.
   -4       The function cannot allocate the queues.
   -3       The device is not open.
   -2       The device is already open.
   -1       The device identifier is invalid or unsupported.

If this function is called with both queue sizes set to zero, the return value is
-2 if the device is already open, or -4 if the device is not open.

Comments
--------

Windows allows COM ports 1 through 9 and LPT ports 1 through 3. If the device
driver does not support a communications port number, the OpenComm() function
will fail.

Sample Code
-----------

The following code example uses the OpenComm() function and FOXTOOLS.FLL to open
COM1. (This example can be found in FOXPROW\GOODIES\FOXTOOLS\DIALER.PRG.)

     *-------------------- dialer.prg ------------------------

     * Sample program to output to comm port
     * Uses FoxTools library for generic DLL access

     SET LIBRARY TO SYS(2004)+"foxtools.fll" ADDITIVE

     opencomm = REGFN("OpenComm", "CII", "I")
     writecomm = REGFN("WriteComm", "ICI", "I")
     closecomm = REGFN("CloseComm", "I", "I")

     com1 = CALLFN(opencomm, "COM1:", 100, 100)
     s = "ATDT 5551212" + chr(13)
     =CALLFN(writecomm, com1, s, len(s))

     WAIT WINDOW "Press any key to hang up"
     s = "ATH0" + chr(13)
     =CALLFN(writecomm, com1, s, len(s))

     =CALLFN(closecomm, com1)

     RELEASE LIBRARY SYS(2004)+"foxtools.fll"

NOTE: In reference to the applicability of the OpenComm() function to Visual
FoxPro for Windows, the 32-bit Foxtools.fll returns a handle to the RegFN() call
provided that it passes the optional 4th argument, which is "USER.DLL." Here is
an example:

     hnd = RegFN("OpenComm","CCC","I","User.dll")

REFERENCES
==========

The above information can also be found in the Microsoft Windows Software
Development Kit (SDK) "Programmer's Reference Volume 2: Functions" [describes
OpenComm()] and the "Programmer's Reference Volume 3: Messages, Structures, and
Macros" (describes the returned values). The online Help file for the
Professional Version of Visual C++ also contains this information.

Additional query words: FoxWin 2.50

======================================================================
Keywords          : kbcode 
Technology        : kbAudDeveloper kbFoxproSearch kbFoxPro260 kbFoxPro250 kbFoxPro250a kbFoxPro250b kbFoxPro260a
Version           : 2.50 2.50a 2.50b 2.60 2.60a

=============================================================================

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