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

getNativeSymbolInfo {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 (http://CRAN.R-project.org/doc/Rnews/).

### See Also

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

### Examples

    library(stats) # normally loaded
    getNativeSymbolInfo("dansari")

    getNativeSymbolInfo(symbol.For("hcass2"))

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