Utility functions for working with foreign C data types

Functions for low-level operations on C pointers as well as helper functions and objects to handle C float arrays and strings.

Usage

is.nullptr(x)

as.externalptr(x)
is.externalptr(x)

floatraw(n)
as.floatraw(x)
floatraw2numeric(x)

ptr2str(x)
strarrayptr(x)
strptr(x)

offset_ptr(x, offset)

Arguments

x: an R object.
n: number of elements to allocate.
offset: a offset given in bytes.

Details

is.nullptr tests if the external pointer given by x represents a C NULL pointer.

as.externalptr returns an external pointer to the data area of atomic vector given by x. The external pointer holds an additional reference to the x R object to prevent it from garbage collection.

is.externalptr tests if the object given by x is an external pointer.

floatraw creates an array with a capacity to store n single-precision C float values. The array is implemented via a raw vector.

as.floatraw coerces a numeric vector into a single-precision C float vector. Values given by x are converted to C float values and stored in the R raw vector via pack. This function is useful when calling foreign functions that expect a C float pointer via dyncall.

floatraw2numeric coerces a C float (raw) vector to a numeric vector.

ptr2str, strarrayptr, strptr are currently experimental.

offset_ptr creates a new external pointer pointing to x plus the byte offset. If x is given as an external pointer, the address is increased by the offset, or, if x is given as a atomic vector, the address of the data (pointing to offset zero) is taken as basis and increased by the offset. The returned external pointer is protected (as offered by the C function R_MakeExternalPtr) by the external pointer x.

Value

A logical value is returned by is.nullptr and is.externalptr.

as.externalptr and offset_ptr returns an external pointer value. floatraw and as.floatraw return an atomic vector of type raw tagged with class 'floatraw'. floatraw2numeric

returns a numeric atomic vector.

Examples

is.nullptr(NULL)
#> [1] FALSE

one <- as.externalptr(1)
is.externalptr(one)
#> [1] TRUE

floatraw(1)
#> [1] 00 00 00 00
#> attr(,"class")
#> [1] "floatraw"

floats <- as.floatraw(1:10)
all.equal(floatraw2numeric(floats), 1:10)
#> [1] TRUE