Obtain a Description of one or more Native (C/Fortran) Symbols
This finds and returns a description of one or more dynamically loaded
or exported built-in native symbols. For each name, it
returns information about the name of the symbol, the library in which
it is located and, if available, the number of arguments it expects
and by which interface it should be called (i.e
.External). Additionally, it returns the address of the
symbol and this can be passed to other C routines. Specifically, this
provides a way to explicitly share symbols between different
dynamically loaded package libraries. Also, it provides a way to
query where symbols were resolved, and aids diagnosing strange
behavior associated with dynamic resolution.
getNativeSymbolInfo(name, PACKAGE, unlist = TRUE, withRegistrationInfo = FALSE)
- the name(s) of the native symbol(s).
- an optional argument that specifies to which
DLL to restrict the search for this symbol. If this is
"base", we search in the R executable itself.
- a logical value which controls how the result is
returned if the function is called with the name of a single symbol.
TRUEand the number of symbol names in
nameis one, then the
NativeSymbolInfoobject is returned. If it is
FALSE, then a list of
NativeSymbolInfoobjects is returned. This is ignored if the number of symbols passed in
nameis more than one. To be compatible with earlier versions of this function, this defaults to
- a logical value indicating whether, if
TRUE, to return information that was registered with R about the symbol and its parameter types if such information is available, or if
FALSEto return just the address of the symbol.
This uses the same mechanism for resolving symbols as is used
in all the native interfaces (
If the symbol has been explicitly registered by the DLL
in which it is contained, information about the number of arguments
and the interface by which it should be called will be returned.
Otherwise, a generic native symbol object is returned.
Generally, a list of
- the name of the symbol, as given by the
FALSE, this is the native memory address of the symbol which can be used to invoke the routine, and also to compare with other symbol addresses. This is an external pointer object and of class
TRUEand registration information is available for the symbol, then this is an object of class
RegisteredNativeSymboland is a reference to an internal data type that has access to the routine pointer and registration information. This too can be used in calls to
- a list containing 3 elements:
If the routine was explicitly registered by the dynamically loaded
library, the list contains a fourth field
- the short form of the library name which can be used
as the value of the
PACKAGEargument in the different native interface functions.
- the fully qualified name of the DLL.
- a logical value indicating whether dynamic resolution is used when looking for symbols in this library, or only registered routines can be located.
- the number of arguments that should be passed in a call to this routine. Additionally, the list will have an additional class, being
NativeSymbolInfoelements whose elements can be indexed by the elements of
namein the call. Each
NativeSymbolInfoobject is a list containing the following elements:
ExternalRoutinecorresponding to the R interface by which it should be invoked.If any of the symbols is not found, an error is raised.If
namecontains only one symbol name and
TRUE, then the single
NativeSymbolInfois returned rather than the list containing that one element.
One motivation for accessing this reflectance information is to be
able to pass native routines to C routines as function pointers in C.
This allows us to treat native routines and R functions in a similar
manner, such as when passing an R function to C code that makes
callbacks to that function at different points in its computation
nls). Additionally, we can resolve the symbol
just once and avoid resolving it repeatedly or using the internal
For information about registering native routines, see In Search of C/C++ & FORTRAN Routines, R-News, volume 1, number 3, 2001, p20--23 (http://cran.r-project.org/doc/Rnews/Rnews_2001-3.pdf).