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How to process char string on char in XS code

Suppose that such a piece of code exists:

  my $str = 'some text';
  my $result = my_subroutine($str);

and my_subroutine()should be implemented as Perl XS code. For example, it can return the sum of bytes of a string (unicode).

Does XS code handle the string (a) char char, as a general method, and (b) byte by byte if the string consists of a subset of ASCII codes (a built-in function to convert string srtucture to char [] from the source data)?

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XS UTF-8. , , char *, , . UTF-8, XS, Unicode Support perlapi

http://cpansearch.perl.org/src/PEVANS/Tickit-0.15/lib/Tickit/Utils.xs

int textwidth(str)
    SV *str
  INIT:
    STRLEN len;
    const char *s, *e;

  CODE:
    RETVAL = 0;

    if(!SvUTF8(str)) {
      str = sv_mortalcopy(str);
      sv_utf8_upgrade(str);
    }

    s = SvPV_const(str, len);
    e = s + len;

    while(s < e) {
      UV ord = utf8n_to_uvchr(s, e-s, &len, (UTF8_DISALLOW_SURROGATE
                                               |UTF8_WARN_SURROGATE
                                               |UTF8_DISALLOW_FE_FF
                                               |UTF8_WARN_FE_FF
                                               |UTF8_WARN_NONCHAR));
      int width = wcwidth(ord);
      if(width == -1)
        XSRETURN_UNDEF;

      s += len;
      RETVAL += width;
    }

  OUTPUT:
    RETVAL

, , , wcwidth().

+3

:

STRLEN len;
char* buf = SvPVbyte(sv, len);

while (len--) {
   char byte = *(buf++);

   ... do something with byte ...
}

:

STRLEN len;
U8* buf = SvPVutf8(sv, len);

while (len) {
   STRLEN ch_len;
   UV ch = utf8n_to_uvchr(buf, len, &ch_len, 0);
   buf += ch_len;
   len -= ch_len;

   ... do something with ch ...
}
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