On 05/27/2018 05:49 PM, Nick Kew wrote: >> On 27 May 2018, at 03:40, Simon Walter <simon@xxxxxxxxxx> wrote: >> >> Hi everyone, >> >> First of all, I am not sure if this is the right place to ask this. >> Please send me to the appropriate mailing list. Thanks. > > What's the context? Given where you asked, I'll guess you're writing > a module for your web server, in which case, there's a modules-dev list > for the next question. Thanks. Maybe I will ask there next time. Though, no I am not writing a module. >> I want to know basically what the difference is between a table and a >> hash table - regarding the APR implementation. > > The best place to look at APR is the source header files, which are the > level at which it's most comprehensively documented and easy to follow. I looked at those just now and it seems that the Doxygen generated docs really are generated from the header files (as advertised) and don't explain much regarding my question. >> The one difference that stands out to me is that I can iterate over a >> hash. So is a hash like a table with a linked list? > > No. > >> Perhaps a table can also be iterated over too. I haven't used tables yet > > You can iterate over a table, too: use its underlying array. > >> I see function names containing >> "merge" and "append", but the docs do not state how this is done. > > The docs in the header files are pretty clear. Yes, except: "...the docs do not state how this is done." > > Also worth bearing in mind, apr_table's more esoteric functions originate in the > standards for manipulating HTTP headers. If in doubt, assume the behaviour > follows HTTP. Good to know, thanks. > > Why not start with the simple: a C array of pointers void* my_array[N_ELTS], > or a linked list? Once you've thought through the problems with those, you're > in a position to decide what struct will best serve you. > > FWIW, the situation where I find an APR array helps most often over a linked > list is in making life easier in a configuration merge function. > Interesting. Thanks. I thought maybe one of those "modules" (in the subject line) might be implemented like a linked list or some other good idea - since the APR is full of good ideas. I already use hash and tables. But I guess I will not use either for this data. To anyone else wondering the same thing: apr_array_append calls apr_array_cat which copies memory - not just a pointer or some trivial amount. apr_hash_merge allocates memory for the size of the combined hash. I didn't take time read further when I saw those lines. Tables are based on arrays. So I can't use those either in this situation. I can't see any copying with skip lists, but I haven't read the code in it's entirety. Best regards, Simon --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscribe@xxxxxxxxxxxxxxxx For additional commands, e-mail: users-help@xxxxxxxxxxxxxxxx
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