[Xlw-cvs] SF.net SVN: xlw: [547] branches/R030000f0-branch/xlw/docs/pages/faq.txt

[<eri...@us...>]

Revision: 547
          http://xlw.svn.sourceforge.net/xlw/?rev=547&view=rev
Author:   ericehlers
Date:     2008-06-01 07:15:24 -0700 (Sun, 01 Jun 2008)

Log Message:
-----------
update docs

Modified Paths:
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    branches/R030000f0-branch/xlw/docs/pages/faq.txt

Modified: branches/R030000f0-branch/xlw/docs/pages/faq.txt
===================================================================
--- branches/R030000f0-branch/xlw/docs/pages/faq.txt	2008-05-28 10:12:43 UTC (rev 546)
+++ branches/R030000f0-branch/xlw/docs/pages/faq.txt	2008-06-01 14:15:24 UTC (rev 547)
@@ -3,6 +3,16 @@
 
 \page faq Frequently Asked Questions
 
+\section faq_new New FAQ
+
+These are FAQs that have arisen since the release of XLW version 3.0.
+
+- \ref NumArgs
+
+\section faq_old Old FAQ
+
+This is the original FAQ that accompanied XLW version 1.0.
+
 - \ref WhenCom
 - \ref WhenNotCom
 - \ref IsItCpp
@@ -10,6 +20,28 @@
 - \ref diffxlldll
 - \ref sr1
 
+\section NumArgs How Many Arguments Are Supported For Addin Functions?
+
+Excel 2007 (and XLW 3.0) support user defined functions with up to 255
+arguments.
+
+Excel versions up to and including 2003 have a limit of 30 function arguments.
+But there is an effective limit of 20 arguments for user defined functions.
+This is because you must register your function by calling xlfRegister, which
+is itself limited to 30 arguments.  xlfRegister uses 10 of its arguments to
+register the function, leaving 20 slots for the descriptions of the arguments
+to your addin function.  XLW ought to raise an exception on an attempt to
+register a function with more than 20 arguments under Excel <= 2003, but it
+doesn't - the error is forwarded to Excel, which silently fails to register
+the function.
+
+It is in fact possible to register a user defined function with up to 30
+arguments, by omitting descriptions for arguments beyond the 20th.  The 21st
+and later arguments are valid but appear in the Function Wizard with no
+descriptions.  XLW doesn't support this trick.
+
+The limit can be circumvented in any case with an argument list.
+
 \section WhenCom When should I use COM?
 The COM interface based on former OLE 2.0 offers a different approach than the
 one used by the C API. A full discussion is beyond the scope of this document


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