1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include <cstddef> // size_t
10#include <cwchar> // mbstate_t
11#include <limits.h> // MB_LEN_MAX
12#include <string.h> // wmemcpy
13
14// Returns the number of wide characters found in the multi byte sequence `src`
15// (of `src_size_bytes`), that fit in the buffer `dst` (of `max_dest_chars`
16// elements size). The count returned excludes the null terminator.
17// When `dst` is NULL, no characters are copied to `dst`.
18// Returns (size_t) -1 when an invalid sequence is encountered.
19// Leaves *`src` pointing to the next character to convert or NULL
20// if a null character was converted from *`src`.
21_LIBCPP_EXPORTED_FROM_ABI size_t mbsnrtowcs(
22 wchar_t* __restrict dst,
23 const char** __restrict src,
24 size_t src_size_bytes,
25 size_t max_dest_chars,
26 mbstate_t* __restrict ps) {
27 const size_t terminated_sequence = static_cast<size_t>(0);
28 const size_t invalid_sequence = static_cast<size_t>(-1);
29 const size_t incomplete_sequence = static_cast<size_t>(-2);
30
31 size_t source_converted;
32 size_t dest_converted;
33 size_t result = 0;
34
35 // If `dst` is null then `max_dest_chars` should be ignored according to the
36 // standard. Setting `max_dest_chars` to a large value has this effect.
37 if (dst == nullptr)
38 max_dest_chars = static_cast<size_t>(-1);
39
40 for (dest_converted = source_converted = 0;
41 source_converted < src_size_bytes && (!dst || dest_converted < max_dest_chars);
42 ++dest_converted, source_converted += result) {
43 // Converts one multi byte character.
44 // If result (char_size) is greater than 0, it's the size in bytes of that character.
45 // If result (char_size) is zero, it indicates that the null character has been found.
46 // Otherwise, it's an error and errno may be set.
47 size_t source_remaining = src_size_bytes - source_converted;
48 size_t dest_remaining = max_dest_chars - dest_converted;
49
50 if (dst == nullptr) {
51 result = mbrtowc(nullptr, *src + source_converted, source_remaining, ps);
52 } else if (dest_remaining >= source_remaining) {
53 // dst has enough space to translate in-place.
54 result = mbrtowc(dst + dest_converted, *src + source_converted, source_remaining, ps);
55 } else {
56 /*
57 * dst may not have enough space, so use a temporary buffer.
58 *
59 * We need to save a copy of the conversion state
60 * here so we can restore it if the multibyte
61 * character is too long for the buffer.
62 */
63 wchar_t buff[MB_LEN_MAX];
64 mbstate_t mbstate_tmp;
65
66 if (ps != nullptr)
67 mbstate_tmp = *ps;
68 result = mbrtowc(buff, *src + source_converted, source_remaining, ps);
69
70 if (result > dest_remaining) {
71 // Multi-byte sequence for character won't fit.
72 if (ps != nullptr)
73 *ps = mbstate_tmp;
74 break;
75 } else {
76 // The buffer was used, so we need copy the translation to dst.
77 wmemcpy(dst, buff, result);
78 }
79 }
80
81 // Don't do anything to change errno from here on.
82 if (result == invalid_sequence || result == terminated_sequence || result == incomplete_sequence) {
83 break;
84 }
85 }
86
87 if (dst) {
88 if (result == terminated_sequence)
89 *src = nullptr;
90 else
91 *src += source_converted;
92 }
93 if (result == invalid_sequence)
94 return invalid_sequence;
95
96 return dest_converted;
97}
98

source code of libcxx/src/support/ibm/mbsnrtowcs.cpp