tidyCpp: Tidy C++ wrapping of the C API for R

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tidyCpp: Tidy C++ wrapping of the C API for R

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About

The C API of the R language and environment is robust, yet a little awkward for C++ programmers. This package wraps a tidy layer of header functions around it.

Examples

A recent motivating example is from the dang package which includes one unexported Base R function written in C. The original version is here. While short enough, we found working with a tidier version easier and more enjoyable. We include an abbreviated version (minus the copyright header) here:

 #include <tidyCpp>
 
 extern "C" {
 
 // cf src/library/tools/src/text.c
SEXP _check_nonASCII(SEXP text, SEXP ignore_quotes) {
 /* Check if all the lines in 'text' are ASCII, after removing
  comments and ignoring the contents of quotes (unless ignore_quotes)
  (which might span more than one line and might be escaped).
 
  This cannot be entirely correct, as quotes and \ might occur as
  part of another character in a MBCS: but this does not happen
  in UTF-8.
  */
 int i, nbslash = 0; /* number of preceding backslashes */
 const char *p;
 char quote= '0円';
 Rboolean ign, inquote = FALSE;
 
 if (!R::isString(text)) R::error("invalid input");
 ign = (Rboolean) R::asLogical(ignore_quotes);
 if (ign == NA_LOGICAL) R::error("'ignore_quotes' must be TRUE or FALSE");
 
 for (i = 0; i < R::length(text); i++) {
 p = R::charPointer(R::stringElement(text, i)); // ASCII or not not affected by charset
 inquote = FALSE; /* avoid runaway quotes */
 for (; *p; p++) {
 if (!inquote && *p == '#') break;
 if (!inquote || ign) {
 if ((unsigned int) *p > 127) {
 Rprintf("%s\n", R::charPointer(R::stringElement(text, i)));
 Rprintf("found %x\n", (unsigned int) *p);
 return R::scalarLogical(TRUE);
 }
 }
 if ((nbslash % 2 == 0) && (*p == '"' || *p == '\'')) {
 if (inquote && *p == quote) {
 inquote = FALSE;
 } else if(!inquote) {
 quote = *p;
 inquote = TRUE;
 }
 }
 if (*p == '\\') nbslash++; else nbslash = 0;
 }
 }
 return R::scalarLogical(FALSE);
 }
 
 } // extern "C"

Additions from the tidyCpp wrapper can be identified easily via the R:: namespace. While the code is not hiding its C heritage, we find it overall a little easier to work with. Other examples (see below) show how using tidyCpp can help avoid the very manual and error-prone PROTECT and UNPROTECT and pairs.

For additional examples, please see the Motivation vignette for a longer discussion with more examples, and the files in the snippets/ directory for directly callable code examples.

Author

Dirk Eddelbuettel

License

GPL (>= 2)

Initially created: Mon 12 Oct 2020 04:19:24 PM CDT
Last modified: Sun May 26 10:29:04 CDT 2024