[PD-dev] symbol comparison vs strcmp()

IOhannes m zmölnig zmoelnig at iem.at
Thu Mar 11 22:13:11 CET 2021

On 3/11/21 9:34 PM, Christof Ressi wrote:
>> the main purpose of the the symbol table is, as i understand it, to 
>> make string comparison super-fast (as there's no need to compare each 
>> character but just a simple address). 
> It is only fast if both sides are `t_symbol *`, but if one side includes 
> a call to gensym(), it will be *slower* than a simple strcmp()!
> For example,
> flagsym == gensym("-lib")

funnily enough, this was exactly the line that triggered my query.
how did you know? (probably because you checked the background of my 
other post)

> is my all means worse than
> !strcmp(flag, "-lib")

well, no. all those specific comparisions for "-lib" are done in loop, 
so you would probably put the gensym("-lib") outside of that loop.

> First of all, these are not the performance critical parts of Pd and 
> most of the strings in question are very short, anyway.
> Secondly, for symbol comparison to make sense, you would have to create 
> all those symbols upfront and store them somewhere. This would indeed 
> pollute the symbol table and add many lines of extra code for no real 
> benefit.

i just find the code mostly more readable.
`!strcmp(flag, "-lib")` is of course fine (apart from the inverse logic 
of strcmp), but `!strcmp(argv[i].a_w.w_symbol->s_name, ">")` is not.
in this case i would happily swap that for a slow `(gensym(">") == 

anyhow, most of those symbols (with the exception of the actual flags), 
are also Pd-objects, so the symtable pollution shouldn't really matter.


-------------- next part --------------
A non-text attachment was scrubbed...
Name: OpenPGP_signature
Type: application/pgp-signature
Size: 840 bytes
Desc: OpenPGP digital signature
URL: <http://lists.puredata.info/pipermail/pd-dev/attachments/20210311/2aad3183/attachment.sig>

More information about the Pd-dev mailing list