lib/mbuiter.h

   1 /* Iterating through multibyte strings: macros for multi-byte encodings.
   2    Copyright (C) 2001, 2005, 2007, 2009-2019 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Bruno Haible <bruno@clisp.org>.  */
  18
  19 /* The macros in this file implement forward iteration through a
  20    multi-byte string, without knowing its length a-priori.
  21
  22    With these macros, an iteration loop that looks like
  23
  24       char *iter;
  25       for (iter = buf; *iter != '\0'; iter++)
  26         {
  27           do_something (*iter);
  28         }
  29
  30    becomes
  31
  32       mbui_iterator_t iter;
  33       for (mbui_init (iter, buf); mbui_avail (iter); mbui_advance (iter))
  34         {
  35           do_something (mbui_cur_ptr (iter), mb_len (mbui_cur (iter)));
  36         }
  37
  38    The benefit of these macros over plain use of mbrtowc is:
  39    - Handling of invalid multibyte sequences is possible without
  40      making the code more complicated, while still preserving the
  41      invalid multibyte sequences.
  42
  43    Compared to mbiter.h, the macros here don't need to know the string's
  44    length a-priori.  The downside is that at each step, the look-ahead
  45    that guards against overrunning the terminating '\0' is more expensive.
  46    The mbui_* macros are therefore suitable when there is a high probability
  47    that only the first few multibyte characters need to be inspected.
  48    Whereas the mbi_* macros are better if usually the iteration runs
  49    through the entire string.
  50
  51    mbui_iterator_t
  52      is a type usable for variable declarations.
  53
  54    mbui_init (iter, startptr)
  55      initializes the iterator, starting at startptr.
  56
  57    mbui_avail (iter)
  58      returns true if there are more multibyte characters available before
  59      the end of string is reached. In this case, mbui_cur (iter) is
  60      initialized to the next multibyte character.
  61
  62    mbui_advance (iter)
  63      advances the iterator by one multibyte character.
  64
  65    mbui_cur (iter)
  66      returns the current multibyte character, of type mbchar_t.  All the
  67      macros defined in mbchar.h can be used on it.
  68
  69    mbui_cur_ptr (iter)
  70      return a pointer to the beginning of the current multibyte character.
  71
  72    mbui_reloc (iter, ptrdiff)
  73      relocates iterator when the string is moved by ptrdiff bytes.
  74
  75    mbui_copy (&destiter, &srciter)
  76      copies srciter to destiter.
  77
  78    Here are the function prototypes of the macros.
  79
  80    extern void          mbui_init (mbui_iterator_t iter, const char *startptr);
  81    extern bool          mbui_avail (mbui_iterator_t iter);
  82    extern void          mbui_advance (mbui_iterator_t iter);
  83    extern mbchar_t      mbui_cur (mbui_iterator_t iter);
  84    extern const char *  mbui_cur_ptr (mbui_iterator_t iter);
  85    extern void          mbui_reloc (mbui_iterator_t iter, ptrdiff_t ptrdiff);
  86    extern void          mbui_copy (mbui_iterator_t *new, const mbui_iterator_t *old);
  87  */
  88
  89 #ifndef _MBUITER_H
  90 #define _MBUITER_H 1
  91
  92 #include <assert.h>
  93 #include <stdbool.h>
  94 #include <stddef.h>
  95 #include <stdlib.h>
  96 #include <string.h>
  97
  98 /* Tru64 with Desktop Toolkit C has a bug: <stdio.h> must be included before
  99    <wchar.h>.
 100    BSD/OS 4.1 has a bug: <stdio.h> and <time.h> must be included before
 101    <wchar.h>.  */
 102 #include <stdio.h>
 103 #include <time.h>
 104 #include <wchar.h>
 105
 106 #include "mbchar.h"
 107 #include "strnlen1.h"
 108
 109 #ifndef _GL_INLINE_HEADER_BEGIN
 110  #error "Please include config.h first."
 111 #endif
 112 _GL_INLINE_HEADER_BEGIN
 113 #ifndef MBUITER_INLINE
 114 # define MBUITER_INLINE _GL_INLINE
 115 #endif
 116
 117 struct mbuiter_multi
 118 {
 119   bool in_shift;        /* true if next byte may not be interpreted as ASCII */
 120   mbstate_t state;      /* if in_shift: current shift state */
 121   bool next_done;       /* true if mbui_avail has already filled the following */
 122   struct mbchar cur;    /* the current character:
 123         const char *cur.ptr             pointer to current character
 124         The following are only valid after mbui_avail.
 125         size_t cur.bytes                number of bytes of current character
 126         bool cur.wc_valid               true if wc is a valid wide character
 127         wchar_t cur.wc                  if wc_valid: the current character
 128         */
 129 };
 130
 131 MBUITER_INLINE void
 132 mbuiter_multi_next (struct mbuiter_multi *iter)
 133 {
 134   if (iter->next_done)
 135     return;
 136   if (iter->in_shift)
 137     goto with_shift;
 138   /* Handle most ASCII characters quickly, without calling mbrtowc().  */
 139   if (is_basic (*iter->cur.ptr))
 140     {
 141       /* These characters are part of the basic character set.  ISO C 99
 142          guarantees that their wide character code is identical to their
 143          char code.  */
 144       iter->cur.bytes = 1;
 145       iter->cur.wc = *iter->cur.ptr;
 146       iter->cur.wc_valid = true;
 147     }
 148   else
 149     {
 150       assert (mbsinit (&iter->state));
 151       iter->in_shift = true;
 152     with_shift:
 153       iter->cur.bytes = mbrtowc (&iter->cur.wc, iter->cur.ptr,
 154                                  strnlen1 (iter->cur.ptr, MB_CUR_MAX),
 155                                  &iter->state);
 156       if (iter->cur.bytes == (size_t) -1)
 157         {
 158           /* An invalid multibyte sequence was encountered.  */
 159           iter->cur.bytes = 1;
 160           iter->cur.wc_valid = false;
 161           /* Whether to set iter->in_shift = false and reset iter->state
 162              or not is not very important; the string is bogus anyway.  */
 163         }
 164       else if (iter->cur.bytes == (size_t) -2)
 165         {
 166           /* An incomplete multibyte character at the end.  */
 167           iter->cur.bytes = strlen (iter->cur.ptr);
 168           iter->cur.wc_valid = false;
 169           /* Whether to set iter->in_shift = false and reset iter->state
 170              or not is not important; the string end is reached anyway.  */
 171         }
 172       else
 173         {
 174           if (iter->cur.bytes == 0)
 175             {
 176               /* A null wide character was encountered.  */
 177               iter->cur.bytes = 1;
 178               assert (*iter->cur.ptr == '\0');
 179               assert (iter->cur.wc == 0);
 180             }
 181           iter->cur.wc_valid = true;
 182
 183           /* When in the initial state, we can go back treating ASCII
 184              characters more quickly.  */
 185           if (mbsinit (&iter->state))
 186             iter->in_shift = false;
 187         }
 188     }
 189   iter->next_done = true;
 190 }
 191
 192 MBUITER_INLINE void
 193 mbuiter_multi_reloc (struct mbuiter_multi *iter, ptrdiff_t ptrdiff)
 194 {
 195   iter->cur.ptr += ptrdiff;
 196 }
 197
 198 MBUITER_INLINE void
 199 mbuiter_multi_copy (struct mbuiter_multi *new_iter, const struct mbuiter_multi *old_iter)
 200 {
 201   if ((new_iter->in_shift = old_iter->in_shift))
 202     memcpy (&new_iter->state, &old_iter->state, sizeof (mbstate_t));
 203   else
 204     memset (&new_iter->state, 0, sizeof (mbstate_t));
 205   new_iter->next_done = old_iter->next_done;
 206   mb_copy (&new_iter->cur, &old_iter->cur);
 207 }
 208
 209 /* Iteration macros.  */
 210 typedef struct mbuiter_multi mbui_iterator_t;
 211 #define mbui_init(iter, startptr) \
 212   ((iter).cur.ptr = (startptr), \
 213    (iter).in_shift = false, memset (&(iter).state, '\0', sizeof (mbstate_t)), \
 214    (iter).next_done = false)
 215 #define mbui_avail(iter) \
 216   (mbuiter_multi_next (&(iter)), !mb_isnul ((iter).cur))
 217 #define mbui_advance(iter) \
 218   ((iter).cur.ptr += (iter).cur.bytes, (iter).next_done = false)
 219
 220 /* Access to the current character.  */
 221 #define mbui_cur(iter) (iter).cur
 222 #define mbui_cur_ptr(iter) (iter).cur.ptr
 223
 224 /* Relocation.  */
 225 #define mbui_reloc(iter, ptrdiff) mbuiter_multi_reloc (&iter, ptrdiff)
 226
 227 /* Copying an iterator.  */
 228 #define mbui_copy mbuiter_multi_copy
 229
 230 _GL_INLINE_HEADER_END
 231
 232 #endif /* _MBUITER_H */