# CallExternal

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##### Modern Interfaces to C/C++ code

Functions to pass R objects to compiled C/C++ code that has been loaded into R.

Keywords
programming
##### Usage
.Call(.NAME, …, PACKAGE)
.External(.NAME, …, PACKAGE)
##### Arguments
.NAME

a character string giving the name of a C function, or an object of class "NativeSymbolInfo", "RegisteredNativeSymbol" or "NativeSymbol" referring to such a name.

arguments to be passed to the compiled code. Up to 65 for .Call.

PACKAGE

if supplied, confine the search for a character string .NAME to the DLL given by this argument (plus the conventional extension, .so, .dll, …).

This argument follows ... and so its name cannot be abbreviated.

This is intended to add safety for packages, which can ensure by using this argument that no other package can override their external symbols, and also speeds up the search (see ‘Note’).

##### Details

The functions are used to call compiled code which makes use of internal R objects, passing the arguments to the code as a sequence of R objects. They assume C calling conventions, so can usually also be used for C++ code.

For details about how to write code to use with these functions see the chapter on ‘System and foreign language interfaces’ in the ‘Writing R Extensions’ manual. They differ in the way the arguments are passed to the C code: .External allows for a variable or unlimited number of arguments.

These functions are primitive, and .NAME is always matched to the first argument supplied (which should not be named). For clarity, avoid using names in the arguments passed to … that match or partially match .NAME.

##### Value

An R object constructed in the compiled code.

##### Note

If one of these functions is to be used frequently, do specify PACKAGE (to confine the search to a single DLL) or pass .NAME as one of the native symbol objects. Searching for symbols can take a long time, especially when many namespaces are loaded.

You may see PACKAGE = "base" for symbols linked into R. Do not use this in your own code: such symbols are not part of the API and may be changed without warning.

PACKAGE = "" used to be accepted (but was undocumented): it is now an error.

##### Header files for external code

Writing code for use with these functions will need to use internal R structures defined in Rinternals.h and/or the macros in Rdefines.h.

##### References

Chambers, J. M. (1998) Programming with Data. A Guide to the S Language. Springer. (.Call.)

dyn.load, .C, .Fortran.