ERDEV, ERDEV$ Functions
 ----------------------------------------------------------------------------


 Action

 Provide device-specific status information after an error.


 Syntax

  ERDEV
 ERDEV$


 Remarks

  ERDEV is an integer function that returns an error code from the last
 device that generated a critical error.  ERDEV$ is a string function that
 returns the name of the device that generated the error. Because  ERDEV and
 ERDEV$ return meaningful information only after an error, they usually are
 used in error-handling routines specified by an  ON ERROR statement.

  ERDEV$ contains the 8-byte character device name if the error is on a
 character device, such as a printer, or the 2-byte block name (A., B., etc.)
 if the device is not a character device. It contains the 3-byte block name
 (COM) if the communications port experiences a timeout.

  ERDEV is set by the critical error handler (interrupt 24H) when DOS detects
 a critical DOS call error. It also is set by a timeout error on the
 communications port and indicates which option in the  OPEN  COM statement
 (CD, CS, or DS) is experiencing the timeout.

  ERDEV returns an integer value that contains information about the error.
 For block and character device errors, the low byte of  ERDEV contains the
 DOS error code. For block devices only, the high byte contains
 device-attribute information.

 For  COM timeout errors,  ERDEV returns a value corresponding to the source
 of the timeout. For more information, see the entry for the  OPEN  COM
 statement.

 Assuming an  ERDEV return value of x, the following program lines generate
 the DOS error code (low byte) and device attribute information (high byte).

 DosErrCode = x AND &HFF' Low byte of ERDEV.
 DevAttr = (x AND &HFF00) \ 256   ' High byte of ERDEV.

 For more information about device-attribute words, see the  Microsoft MS-DOS
  Programmer's  Reference, or books such as  The Peter Norton Guide to the
 IBM PC or  Advanced MS-DOS.


 Use  ERDEV only in DOS.


 Example

 The following example prints the values of  ERDEV and  ERDEV$ after the
 program generates an error attempting to open a file.

 DEFINT A-Z
 ON ERROR GOTO ErrorHandler' Indicate first line of error handler.
 OPEN "A.JUNK.DAT" FOR INPUT AS #1' Attempt to open the file.
 END

 ErrorHandler.
 PRINT "ERDEV value is "; ERDEV
 PRINT "Device name is "; ERDEV$
 ON ERROR GOTO 0

 Output
 Running the program with drive A unlatched produces the following output (2 i

 ERDEV value is  2
 Device name is A.