README.md

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';
    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)



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tidyCpp documentation built on March 8, 2021, 1:15 a.m.