In What Version of AutoCAD Was My File Saved?

As I start thinking about deploying AutoCAD^® Architecture and AutoCAD^® MEP 2018, I have been considering how to manage having multiple file formats in use at the same time. Not that we have not had to deal with that in the past; but we have been primarily using 2013-format releases for quite some time, so I will need to make and keep users aware of the fact that once a file is saved in the 2018 format, there is no going back.

One "trick" I personally have used to check on the file format of a file prior to opening it is discussed in this Autodesk Knowledge Network article. You can determine the file format of an AutoCAD^® drawing file by opening the file in a plain text editor (like Notepad) and looking at the first six characters. That article lists the "codes" for the 2000 through 2013 file formats. Shaan Hurley, in this article in his Between the Lines blog, has a more complete listing of the codes, including the fact that the new 2018 file format is AC1032. Scroll down to the bottom of the article, under the DWG File History header, for the full listing.

One drawback to that trick is that really large files can take quite some time to open in Notepad, and there is always the risk (however small) that you could accidentally make a change and then save the file in Notepad. It occurred to me that an AutoLISP routine ought to be able to use the read-line function to read the first line of a drawing file, extract the first six characters, and then report the results; this proved to be true. You do have to have an instance of AutoCAD open first, but if you do, the routine works much faster than opening in Notepad for large files, and there is no risk of changing the file. I chose to limit the versions for which it tests to the AC1001 (Version 2.2) format. I was not able to fully test all of those, as I was unable to find a file in my archives that was last saved in anything earlier than Release 9 (AC1004). If your archives include files of earlier vintage, you could extend the code for the earlier versions listed in Shaan's article, assuming that those older files have the "code" in the first six characters.

(defun C:FMT ( / file1 sfile1 sline1 stext1)
  (setq sfile1 (getfiled "Select Drawing File" "" "dwg" 0)
        file1  (open sfile1 "r")
  ) ;_ End setq.
  (if file1
    (progn
      (setq sline1 (read-line file1)
            stext1 (substr sline1 1 6)
      ) ;_ End setq.
      (close file1)
      (cond    ; Condition A.
        ((= "AC1032" stext1)
         (alert
           (strcat
             "Header = AC1032."
             "\nFile " sfile1
             "\nis saved in the 2018 file format."
           ) ;_ End strcat.
         ) ;_ End alert.
        ) ;_ End condition A1.
        ((= "AC1027" stext1)
         (alert
           (strcat
             "Header = AC1027."
             "\nFile " sfile1
             "\nis saved in the 2013 file format."
           ) ;_ End strcat.
         ) ;_ End alert.
        ) ;_ End condition A2.
        ((= "AC1024" stext1)
         (alert
           (strcat
             "Header = AC1024."
             "\nFile " sfile1
             "\nis saved in the 2010 file format."
           ) ;_ End strcat.
         ) ;_ End alert.
        ) ;_ End condition A3.
        ((= "AC1021" stext1)
         (alert
           (strcat
             "Header = AC1021."
             "\nFile " sfile1
             "\nis saved in the 2007 file format."
           ) ;_ End strcat.
         ) ;_ End alert.
        ) ;_ End condition A4.
        ((= "AC1018" stext1)
         (alert
           (strcat
             "Header = AC1018."
             "\nFile " sfile1
             "\nis saved in the 2004 file format."
           ) ;_ End strcat.
         ) ;_ End alert.
        ) ;_ End condition A5.
        ((= "AC1015" stext1)
         (alert
           (strcat
             "Header = AC1015."
             "\nFile " sfile1
             "\nis saved in the 2000 file format."
           ) ;_ End strcat.
         ) ;_ End alert.
        ) ;_ End condition A6.
        ((= "AC1014" stext1)
         (alert
           (strcat
             "Header = AC1014."
             "\nFile " sfile1
             "\nis saved in the R14 file format."
           ) ;_ End strcat.
         ) ;_ End alert.
        ) ;_ End condition A7.
        ((= "AC1012" stext1)
         (alert
           (strcat
             "Header = AC1012."
             "\nFile " sfile1
             "\nis saved in the R13 file format."
           ) ;_ End strcat.
         ) ;_ End alert.
        ) ;_ End condition A8.
        ((= "AC1009" stext1)
         (alert
           (strcat
             "Header = AC1009."
             "\nFile " sfile1
             "\nis saved in the R11/R12 file format."
           ) ;_ End strcat.
         ) ;_ End alert.
        ) ;_ End condition A9.
        ((= "AC1006" stext1)
         (alert
           (strcat
             "Header = AC1006."
             "\nFile " sfile1
             "\nis saved in the R10 file format."
           ) ;_ End strcat.
         ) ;_ End alert.
        ) ;_ End condition A10.
        ((= "AC1004" stext1)
         (alert
           (strcat
             "Header = AC1004."
             "\nFile " sfile1
             "\nis saved in the R9 file format."
           ) ;_ End strcat.
         ) ;_ End alert.
        ) ;_ End condition A11.
        ((= "AC1003" stext1)
         (alert
            (strcat
             "Header = AC1003."
             "\nFile " sfile1
             "\nis saved in the Version 2.60 file format."
           ) ;_ End strcat.
         ) ;_ End alert.
        ) ;_ End condition A12.
        ((= "AC1002" stext1)
         (alert
           (strcat
             "Header = AC1002."
             "\nFile " sfile1
             "\nis saved in the Version 2.50 file format."
           ) ;_ End strcat.
         ) ;_ End alert.
        ) ;_ End condition A13.
        ((= "AC1001" stext1)
         (alert
           (strcat
             "Header = AC1001."
             "\nFile " sfile1
             "\nis saved in the Version 2.22 file format."
           ) ;_ End strcat.
         ) ;_ End alert.
        ) ;_ End condition A14.
        (T
         (alert
           (strcat
             "Header = "
             stext1
             "\nFile " sfile1
             "\nis saved in an unknown file format."
           ) ;_ End strcat.
         ) ;_ End alert.
        ) ;_ End condition A15.
      ) ;_ End condition A.
    ) ;_ End progn.
    (prompt "\nNo file selected. ")
  ) ;_ End if.
  (prin1)
) ;_ End C:FMT

Here is an example of the alert message that will be displayed.