Re: [Rd] string comparison

From: Duncan Murdoch <murdoch_at_stats.uwo.ca>
Date: Thu, 07 Aug 2008 13:50:51 -0400

On 8/7/2008 11:20 AM, Prof Brian Ripley wrote:
> It is not safe to rely on pointer comparisons until R 2.8.0. Currently it
> is easy to get CHARSXPs that are not in the cache: it is not impossible in
> 2.8.0, but you have to know how to 'break and enter'.
>
> In your code you are comparing a CHARSXP and a SYMSXP. You want to
> use charChance = mkChar("chance") and then make it precious
> (R_PreciousObject).

That's R_PreserveObject (which puts the object into an internal structure called R_PreciousList).

Duncan Murdoch

>
> On Thu, 7 Aug 2008, Kjell Konis wrote:
>
>> Hi,
>>
>> I have a package where I do things like this a lot:
>>
>> if(strncmp(CHAR(asChar(Scategory)), "chance", 6) == 0)
>> category = h_category_chance;
>> else if(strncmp(CHAR(asChar(Scategory)), "utility", 7) == 0)
>> category = h_category_utility;
>> else if(strncmp(CHAR(asChar(Scategory)), "decision", 8) == 0)
>> category = h_category_decision;
>> else if(strncmp(CHAR(asChar(Scategory)), "instance", 8) == 0)
>> category = h_category_instance;
>> else
>> category = h_category_error;
>>
>> I would like to replace the strncmps with pointer comparisons so I set up
>> some global variables in the R_init_myDLL function like this:
>>
>> charChance = install("chance")
>> <etc.>
>>
>> but I can't seem to get the comparison to work. I want to do something like
>>
>> if(CHAR(asChar(Scategory)) == charChance)
>> category = h_category_chance;
>>
>> but category always ends up being h_category_error. Any pointers would be
>> appreciated.
>>
>> Thanks,
>> Kjell
>>
>> ______________________________________________
>> R-devel_at_r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>



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https://stat.ethz.ch/mailman/listinfo/r-devel Received on Thu 07 Aug 2008 - 17:53:06 GMT

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