[R-pkg-devel] How to pass a connection into a C function (R 3.2)

[Duncan Murdoch]

On 21/01/2016 1:07 PM, Tom Quarendon wrote:
> So upshot is that I can only do why I want by using the function that's not part of the api, or just not using connections at all and just using normal C file io, opened from C, and simply pass the file name in instead, rather than a proper connection object?

You could also call R from C to do the I/O for you.

Duncan Murdoch

>> On 21 Jan 2016, at 6:04 pm, Duncan Murdoch <murdoch.duncan at gmail.com> wrote:
>>
>>> On 21/01/2016 12:50 PM, Tom Quarendon wrote:
>>> But that's what I want to do, create the connection in R code and pass it on to the C function.
>>> My question is, how do I do that?
>>> You appear to need the C getConnection entry point, but it's not part of the API.
>>> So I'm wondering how I'm supposed to do what you describe.
>>
>> Sorry, my advice was wrong.  I remembered that we exposed code to create new connections, and assumed it had some code to work with them, but it doesn't.
>>
>> Duncan Murdoch
>>>
>>> Sorry if I was unclear.
>>>
>>> Sent from my iPhone
>>>
>>>>> On 21 Jan 2016, at 5:44 pm, Duncan Murdoch <murdoch.duncan at gmail.com> wrote:
>>>>>
>>>>> On 21/01/2016 11:39 AM, Tom Quarendon wrote:
>>>>> I would like to implement a package that contains a C function that writes to a connection.
>>>>> So the R_ext/Connections.h defines what a connection IS, but not how to get one.
>>>>>
>>>>> What seems to work is to manually declare
>>>>> Rconnection getConnection(int n);
>>>>> In my C file, and while this works, and I can then use the connection object, it fails package validation with:
>>>>>
>>>>> �Found non-API call to R: �getConnection�
>>>>> Compiled code should not call non-API entry points in R.�
>>>>>
>>>>> So how am I supposed to do this? Is there a way? Or do I just live with the check warning (ideally not)?
>>>>
>>>> The usual way to do that would be to create the connection in R code, and pass it in with your call.
>>>>
>>>> If you don't know what connection you need at the time you call your C code, you can evaluate an R expression from C to do the same, but this is relatively tricky, so I'd advise the other method.
>>>>
>>>> Duncan Murdoch
>>