Mercurial > pub > dyncall > bindings
comparison R/rdyncall/man/packing.Rd @ 0:0cfcc391201f
initial from svn dyncall-1745
| author | Daniel Adler |
|---|---|
| date | Thu, 19 Mar 2015 22:26:28 +0100 |
| parents | |
| children |
comparison
equal
deleted
inserted
replaced
| -1:000000000000 | 0:0cfcc391201f |
|---|---|
| 1 \name{packing} | |
| 2 \alias{.pack} | |
| 3 \alias{packing} | |
| 4 \alias{.unpack} | |
| 5 \title{Handling of foreign C fundamental data types} | |
| 6 \description{Functions to unpack/pack (read/write) foreign C data types from/to R atomic vectors and C data objects such as arrays and pointers to structures.} | |
| 7 \usage{ | |
| 8 .pack(x, offset, sigchar, value) | |
| 9 .unpack(x, offset, sigchar) | |
| 10 } | |
| 11 \arguments{ | |
| 12 \item{x}{atomic vector (logical, raw, integer or double) or external pointer.} | |
| 13 \item{offset}{integer specifying \emph{byte offset} starting at 0.} | |
| 14 \item{sigchar}{character string specifying the C data type by a \link{type signature}.} | |
| 15 \item{value}{R object value to be coerced and packed to a foreign C data type.} | |
| 16 } | |
| 17 \details{ | |
| 18 The function \code{.pack} converts an R \code{value} into a C data type specified by the \link{signature} \code{sigchar} | |
| 19 and it writes the raw C foreign data value at byte position \code{offset} into the object \code{x}. | |
| 20 The function \code{.unpack} extracts a C data type according to the \link{signature} \code{sigchar} | |
| 21 at byte position \code{offset} from the object \code{x} and converts the C value to an R value and returns it. | |
| 22 | |
| 23 Byte \code{offset} calculations start at 0 relative to the first byte in an atomic vectors data area. | |
| 24 | |
| 25 If \code{x} is an atomic vector, a bound check is carried out before read/write access. | |
| 26 Otherwise, if \code{x} is an external pointer, there is only a C NULL pointer check. | |
| 27 } | |
| 28 \value{ | |
| 29 \code{.unpack} returns a read C data type coerced to an R value. | |
| 30 } | |
| 31 \seealso{ | |
| 32 \code{\link{.dyncall}} for details on type signatures. | |
| 33 } | |
| 34 \examples{ | |
| 35 # transfer double to array of floats and back, compare precision: | |
| 36 n <- 6 | |
| 37 input <- rnorm(n) | |
| 38 buf <- raw(n*4) | |
| 39 for (i in 1:n) { | |
| 40 .pack(buf, 4*(i-1), "f", input[i]) | |
| 41 } | |
| 42 output <- numeric(n) | |
| 43 for (i in 1:n) { | |
| 44 output[i] <- .unpack(buf, 4*(i-1), "f") | |
| 45 } | |
| 46 # difference between double and float | |
| 47 difference <- output-input | |
| 48 print( cbind(input,output,difference) ) | |
| 49 } |