package_native_routine_registration_skeleton {tools} | R Documentation

## Write Skeleton for Adding Native Routine Registration to a Package

### Description

Write a skeleton for adding native routine registration to a package.

### Usage

    package_native_routine_registration_skeleton(dir, con = stdout(),
        align = TRUE, character_only = TRUE, include_declarations = TRUE)

### Arguments

`dir` | Top-level directory of a package.
`con` | Connection on which to write the skeleton: can be specified as a file path.
`align` | Logical: should the registration tables be lined up in three columns each?
`character_only` | Logical: should only `.NAME` arguments specified by character strings (and not as names of R objects nor expressions) be extracted?
`include_declarations` | Logical: should the output include declarations (also known as ‘prototypes’) for the registered routines?

### Details

Registration is described in section 5.4.1 of ‘Writing R Extensions’. This function produces a skeleton of the C code which needs to be added to enable registration, conventionally as file ‘src/init.c’ or appended to the sole C file of the package.

This function examines the code in the ‘R’ directory of the package for calls to `.C`, `.Fortran`, `.Call` and `.External` and creates registration information for those it can make sense of. If the number of arguments used cannot be determined it will be recorded as `-1`: such values should be corrected.

Optionally the skeleton will include declarations for the registered routines: they should be checked against the C/Fortran source code, not least as the number of arguments is taken from the R code. For `.Call` and `.External` calls they will often suffice, but for `.C` and `.Fortran` calls the `void *` arguments would ideally be replaced by the actual types. Otherwise declarations need to be included (they may exist earlier in that file if appending to a file, or in a header file which can be included in ‘init.c’).

The default value of `character_only` is appropriate when working on a package without any existing registration: `character_only = FALSE` can be used to suggest updates for a package which has been extended since registration. For the default value, if `.NAME` values are found which are not character strings (e.g. names or expressions) this is noted via a comment in the output.

Packages which used the earlier form of creating R objects for native symbols via additional arguments in a `useDynLib` directive will probably most easily be updated to use registration with `character_only = FALSE`.

If an entry point is used with different numbers of arguments in the package's R code, an entry in the table (and optionally, a declaration) is made for each number, and a comment placed in the output. This needs to be resolved: only `.External` calls can have a variable number of arguments, which should be declared as `-1`.

A surprising number of CRAN packages had calls in R code to native routines not included in the package, which will lead to a ‘loading failed’ error during package installation when the registration C code is added.

Calls which do not name a routine such as `.Call(...)` will be silently ignored.

### Value

None: the output is written to the connection `con`.

### Extracting C/C++ prototypes

There are several tools available to extract function declarations from C or C++ code. For example,

For C code one can use `cproto` (http://invisible-island.net/cproto/cproto.html; Windows executables are available), for example

        cproto -I/path/to/R/include -e *.c

`ctags` (commonly distributed with the OS) covers C and C++., listing all function usages by something like

        ctags -x *.c

. (The ‘Exuberant’ version allows a lot more control.)

### Note

This only examines the ‘R’ directory: it will not find e.g. `.Call` calls used directly in examples, tests etc.

Static code analysis is used to find the `.C` etc calls: it will find those in parts of the R code ‘commented out’ by inclusion in `if(FALSE) { ... }`. On the other hand, it will fail to find the entry points in constructs like

        .Call(if(int) "rle_i" else "rle_d", i, force)

and does not know the value of variables in calls like

        .Call (cfunction, ...)
        .Call(..., PACKAGE="sparseLTSEigen")

(but if `character_only` is false, will extract the first as `"cfunction"`). Calls which have not been fully resolved will be noted via comments in the output file.

Call to entry points in other packages will be ignored if they have an explicit (character string) `PACKAGE` argument.

### See Also

`package.skeleton`.

### Examples

    ## Not run:
    ## with a completed splines/DESCRIPTION file,
    tools::package_native_routine_registration_skeleton('splines',,,FALSE)
    ## produces
    #include <R.h>
    #include <Rinternals.h>
    #include <stdlib.h> // for NULL
    #include <R_ext/Rdynload.h>

    /* FIXME:
       Check these declarations against the C/Fortran source code.
    */

    /* .Call calls */
    extern SEXP spline_basis(SEXP, SEXP, SEXP, SEXP);
    extern SEXP spline_value(SEXP, SEXP, SEXP, SEXP, SEXP);

    static const R_CallMethodDef CallEntries[] = {
        {"spline_basis", (DL_FUNC) &spline_basis, 4},
        {"spline_value", (DL_FUNC) &spline_value, 5},
        {NULL, NULL, 0}
    };

    void R_init_splines(DllInfo *dll)
    {
        R_registerRoutines(dll, NULL, CallEntries, NULL, NULL);
        R_useDynamicSymbols(dll, FALSE);
    }

    ## End(Not run)

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