|
0
|
1 \name{struct}
|
|
|
2 \alias{struct}
|
|
|
3 \alias{new.struct}
|
|
|
4 \alias{as.struct}
|
|
|
5 \alias{parseStructInfos}
|
|
|
6 \alias{parseUnionInfos}
|
|
|
7 \alias{$.struct}
|
|
|
8 \alias{print.struct}
|
|
|
9 \alias{$<-.struct}
|
|
|
10 \title{Allocation and handling of foreign C aggregate data types}
|
|
|
11 \description{Functions for allocation, access and registration of foreign C \code{struct} and \code{union} data type.}
|
|
|
12 \usage{
|
|
|
13 new.struct(type)
|
|
|
14 as.struct(x, type)
|
|
|
15 parseStructInfos(sigs, envir=parent.frame())
|
|
|
16 parseUnionInfos(sigs, envir=parent.frame())
|
|
|
17 \S3method{$}{struct}(x, index)
|
|
|
18 \S3method{$}{struct}(x, index) <- value
|
|
|
19 \S3method{print}{struct}(x, indent=0, \ldots)
|
|
|
20 }
|
|
|
21 \arguments{
|
|
|
22 \item{x}{external pointer or atomic raw vector of S3 class 'struct'.}
|
|
|
23 \item{type}{S3 \link{TypeInfo} Object or character string that names the structure type.}
|
|
|
24 \item{sigs}{character string that specifies several C struct/union type \link{signature}s.}
|
|
|
25 \item{envir}{the environment to install S3 type information object(s).}
|
|
|
26 \item{index}{character string specifying the field name.}
|
|
|
27 \item{indent}{indentation level for pretty printing structures.}
|
|
|
28 \item{value}{value to be converted according to struct/union field type given by field index.}
|
|
|
29 \item{...}{additional arguments to be passed to \code{\link[base]{print}} method.}
|
|
|
30 }
|
|
|
31 \details{
|
|
|
32 References to foreign C data objects are represented by objects of class 'struct'.
|
|
|
33
|
|
|
34 Two reference types are supported:
|
|
|
35
|
|
|
36 \itemize{
|
|
|
37 \item \emph{External pointers} returned by \code{\link{.dyncall}} using a call signature with a \emph{typed pointer} return type signature
|
|
|
38 and pointers extracted as a result of \code{\link{.unpack}} and S3 \code{struct} \code{$}-operators.
|
|
|
39 \item \emph{Internal objects}, memory-managed by R, are allocated by \code{new.struct}:
|
|
|
40 An atomic \code{raw} storage object is returned, initialized with length equal to the byte size of the
|
|
|
41 foreign C data type.
|
|
|
42 }
|
|
|
43
|
|
|
44 In order to access and manipulate the data fields of foreign C aggregate data objects, the \dQuote{$} and \dQuote{$<-} S3 operator methods
|
|
|
45 can be used.
|
|
|
46
|
|
|
47 S3 objects of class \code{struct} have an attribute \code{struct} set to the name of a \code{\link{TypeInfo}} object, which provides the
|
|
|
48 run-time type information of a particular foreign C type.
|
|
|
49
|
|
|
50 The run-time type information for foreign C \code{struct} and \code{union} types need to be registered once via
|
|
|
51 \code{parseStructInfos} and \code{parseUnionInfos} functions.
|
|
|
52 The C data types are specified by \code{sigs}, a signature character string. The formats for both types are described next:
|
|
|
53
|
|
|
54 \strong{Structure type signatures} describe the layout of aggregate \code{struct} C data types.
|
|
|
55 Type Signatures are used within the \sQuote{field-types}. \sQuote{field-names} consists of space separated identifier names and
|
|
|
56 should match the number of fields.
|
|
|
57
|
|
|
58 \tabular{c}{
|
|
|
59 \emph{struct-name} '\code{\{}' \emph{field-types} '\code{\}}' \emph{field-names} '\code{;}' \cr
|
|
|
60 }
|
|
|
61
|
|
|
62 Here is an example of a C \code{struct} type:
|
|
|
63
|
|
|
64 \preformatted{
|
|
|
65 struct Rect \{
|
|
|
66 signed short x, y;
|
|
|
67 unsigned short w, h;
|
|
|
68 \};
|
|
|
69 }
|
|
|
70
|
|
|
71 The corresponding structure type signature is:
|
|
|
72
|
|
|
73 \preformatted{"Rect\{ssSS\}x y w h;"}
|
|
|
74
|
|
|
75 \strong{Union type signatures} describe the components of the \code{union} C data type.
|
|
|
76 Type signatures are used within the \sQuote{field-types}. \sQuote{field-names} consists of space separated identifier names and
|
|
|
77 should match the number of fields.
|
|
|
78
|
|
|
79 \tabular{c}{
|
|
|
80 \emph{union-name} '\code{|}' \emph{field-types} '\code{\}}' \emph{field-names} '\code{;}' \cr
|
|
|
81 }
|
|
|
82
|
|
|
83 Here is an example of a C \code{union} type,
|
|
|
84
|
|
|
85 \preformatted{
|
|
|
86 union Value \{
|
|
|
87 int anInt;
|
|
|
88 float aFloat;
|
|
|
89 struct LongValue aStruct
|
|
|
90 \};
|
|
|
91 }
|
|
|
92
|
|
|
93 The corresponding union type signature is:
|
|
|
94
|
|
|
95 \code{"Value|if<LongValue>}anInt aFloat aStruct;"}
|
|
|
96
|
|
|
97 \code{as.struct} can be used to \emph{cast} a foreign C data reference to a different type.
|
|
|
98 When using an external pointer reference, this can lead quickly to a \strong{fatal R process crash} - like in C.
|
|
|
99 }
|
|
|
100 \seealso{
|
|
|
101 \code{\link{.dyncall}} for type signatures and \code{\link{TypeInfo}} for details on run-time type information S3 objects.
|
|
|
102 }
|
|
|
103 \examples{
|
|
|
104 # Specify the following foreign type:
|
|
|
105 # struct Rect {
|
|
|
106 # short x, y;
|
|
|
107 # unsigned short w, h;
|
|
|
108 # }
|
|
|
109 parseStructInfos("Rect{ssSS}x y w h;")
|
|
|
110 r <- new.struct(Rect)
|
|
|
111 print(r)
|
|
|
112 r$x <- 40
|
|
|
113 r$y <- 60
|
|
|
114 r$w <- 10
|
|
|
115 r$h <- 15
|
|
|
116 print(r)
|
|
|
117 str(r)
|
|
|
118 }
|
|
|
119 \keyword{programming}
|
|
|
120 \keyword{interface}
|
