I've been working on moving the book Creating XPCOM Components[1] from mozilla.org
over to developer.mozilla.org[2]. The migration is in essence complete -- all the
text (sans an XPCOM API Reference which is separately maintained) has been copied,
formatted, surface-edited, and cross-linked, and it is ready for use as long as
you can successfully read between the lines to decide what parts may be less
relevant now than when the book was written (mostly due to the suite->Firefox
transition). I'm now slowly working through the remaining problems I know exist
(with occasional supplements from people who make questions or post comments in
the wiki).
First question: the book contains two separate code snippets related to
AddCategoryEntry (one's explanatory while the other's part of an overall code
exhibit, so they *should* both be the same):
Exhibit A:
nsEmbedCString previous;
rv = catman->AddCategoryEntry("xpcom-startup",
"WebLock",
WebLock_ContractID,
PR_TRUE, // persist category
PR_TRUE, // replace existing
previous);
Exhibit B:
char* previous = nsnull;
rv = catman->AddCategoryEntry("xpcom-startup",
"WebLock",
WebLock_ContractID,
PR_TRUE,
PR_TRUE,
&previous);
Which of these is the preferred way? (We'll ignore the fact that in this
instance it doesn't matter as |previous| is immediately nsMemory::Free'd.)
From my reading of the source code I don't think there's a substantive
difference between the two, but there's no reason to be inconsistent.
Second: while investigating the previous question, I did some source browsing of
AddCategoryEntry[3] to see how the sixth parameter (which returns the "previous
entry, if any" according to IDL) is set. From my reading of the code it looks like
the parameter isn't even used, which would mean the IDL comments are out-of-date.
AddCategoryEntry doesn't itself touch the parameter (and hasn't since 2003), and the only
place it's passed (CategoryNode::AddLeaf[4]) seems to not touch it either. Am I horribly
misreading this code, or do the IDL comments need to be updated?
Thanks in advance for any help I can get here!
Jeff Walden
P.S. -- Any other comments on the migrated version of Creating XPCOM Components
are more than welcome. :-)
1. http://www.mozilla.org/projects/xpcom/book/cxc/html/
2. http://developer.mozilla.org/en/docs/Creating_XPCOM_Components
3.
http://lxr.mozilla.org/mozilla/source/xpcom/components/nsCategoryManager.cpp#583
4.
http://lxr.mozilla.org/mozilla/source/xpcom/components/nsCategoryManager.cpp#286
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