getNativeSymbolInfo           package:base           R Documentation

Obtain a description of a native (C/Fortran) symbol

Description:

     This finds and returns as comprehensive a description of a
     dynamically loaded or ``exported'' built-in native symbol. 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 `.Call',  
     `.C', `.Fortran',  or `.External'). Additionally, it returns the
     address of the symbol and this can be passed to other C routines
     which can invoke. 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.

Usage:

     getNativeSymbolInfo(name, PACKAGE)

Arguments:

    name: the name of the native symbol as used in a call to
          `is.loaded', etc.

 PACKAGE: an optional argument that specifies to which dynamically
          loaded library we restrict the search for this symbol. If
          this is `"base"', we search in the R executable itself.

Details:

     This uses the same mechanism for resolving symbols as is used in
     all the native interfaces (`.Call', etc.). If the symbol has been
     explicitly registered by the shared library 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.

Value:

     If the symbol is not found, an error is raised. Otherwise, the
     value is a list containing the following elements: 

    name: the name of the symbol, as given by the `name' argument.

 address: the native memory address of the symbol which can be used to
          invoke the routine, and also compare with other symbol
          address. This is an external pointer object and of class
          `NativeSymbol'.

 package: a list containing 3 elements:

     name the short form of the library name which can be used as the
          value of the `PACKAGE' argument in the different native
          interface functions.

     path the fully qualified name of the shared library file.

     dynamicLookup a logical value indicating whether dynamic
          resolution is used when looking for symbols in this library,
          or only registered routines can be located. 

numParameters: the number of arguments that should be passed in a call
          to this routine.

     Additionally, the list will have an additional class, being
     `CRoutine',   `CallRoutine', `FortranRoutine' or `ExternalRoutine'
     corresponding to the R interface by which it should be invoked.

Note:

     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 (e.g. `nls'). Additionally, we can
     resolve the symbol just once and avoid resolving it repeatedly or
     using the internal cache. In the future, one may be able to treat
     `NativeSymbol' objects as directly callback objects.

Author(s):

     Duncan Temple Lang

References:

     For information about registering native routines, see ``In Search
     of {C/C++} & {FORTRAN} Routines'', R News, volume 1, number 3,
     2001, p20-23 (<URL: http://CRAN.R-project.org/doc/Rnews/>).

See Also:

     `is.loaded', `.C', `.Fortran', `.External', `.Call', `dyn.load'.

Examples:

     getNativeSymbolInfo("dansari")

     library(mva)
     getNativeSymbolInfo(symbol.For("hcass2"))

