R: Management of .C argument conversion list

getNumCConverters {base} | R Documentation

## Management of .C argument conversion list

### Description

These functions provide facilities to manage the extensible list of converters used to translate R objects to C pointers for use in `.C` calls. The number and a description of each element in the list can be retrieved. One can also query and set the activity status of individual elements, temporarily ignoring them. And one can remove individual elements.

### Usage

    getNumCConverters()
    getCConverterDescriptions()
    getCConverterStatus()
    setCConverterStatus(id, status)
    removeCConverter(id)

### Arguments

`id` | either a number or a string identifying the element of interest in the converter list. A string sis matched against the description strings for each element to identify the element. Integers are specified starting at 1 (rather than 0).
`status` | a logical value specifying whether the element is to be considered active (`TRUE`) or not (`FALSE`).

### Details

The internal list of converters is potentially used when converting individual arguments in a `.C` call. If an argument has a non-trivial class attribute, we iterate over the list of converters looking for the first that ``matches''. If we find a matching converter, we have it create the C-level pointer corresponding to the R object. When the call to the C routine is complete, we use the same converter for that argument to reverse the conversion and create an R object from the current value in the C pointer. This is done separately for all the arguments.

The functions documented here provide R user-level capabilities for investigating and managing the list of converters. There is currently no mechanism for adding an element to the converter list within the R language. This must be done in C code using the routine `R_addToCConverter()`.

### Value

`getNumCConverters` returns an integer giving the number of elements in the list, both active and inactive.
`getCConverterDescriptions` returns a character vector containing the description string of each element of the converter list.
`getCConverterStatus` returns a logical vector with a value for each element in the converter list. Each value indicates whether that converter is active (`TRUE`) or inactive (`FALSE`). The names of the elements are the description strings returned by `getCConverterDescriptions`.
`setCConverterStatus` returns the logical value indicating the activity status of the specified element before the call to change it took effect. This is `TRUE` for active and `FALSE` for inactive.
`removeCConverter` returns `TRUE` if an element in the converter list was identified and removed. In the case that no such element was found, an error occurs.

### Author(s)

Duncan Temple Lang

### References

http://developer.R-project.org/CObjectConversion.pdf

### See Also

`.C`

### Examples

     getNumCConverters()
     getCConverterDescriptions()
     getCConverterStatus()

      old <- setCConverterStatus(1,FALSE)

      setCConverterStatus(1,old)

      removeCConverter(1)
      removeCConverter(getCConverterDescriptions()[1])

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