4 * Implementation of an ISO-C99 conforming btowc() function; note that,
5 * since this considers only one byte for conversion, and a single byte
6 * can never convert to a surrogate pair, this is not susceptible to the
7 * potential wchar_t overflow error, which may occur with functions such
8 * as mbrtowc(), which may need to return surrogate pairs.
12 * Written by Keith Marshall <keith@users.osdn.me>
13 * Copyright (C) 2020, MinGW.org Project
16 * Permission is hereby granted, free of charge, to any person obtaining a
17 * copy of this software and associated documentation files (the "Software"),
18 * to deal in the Software without restriction, including without limitation
19 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
20 * and/or sell copies of the Software, and to permit persons to whom the
21 * Software is furnished to do so, subject to the following conditions:
23 * The above copyright notice, this permission notice, and the following
24 * disclaimer shall be included in all copies or substantial portions of
27 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
28 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
29 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
30 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
31 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
32 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OF OR OTHER
33 * DEALINGS IN THE SOFTWARE.
38 /* For runtime delegation, we need a mechanism for detection of an
39 * implementation, within the default C runtime DLL; we may use the
40 * MinGW dlfcn emulation, to facilitate this.
44 /* We also need <stdio.h>, for EOF.
48 static wint_t __mingw_btowc_fallback( int c )
49 { /* Fallback function, providing an implementation of the btowc()
50 * function, when none is available within the Microsoft runtime.
51 * This performs an MBCS to wchar_t conversion on the given single
52 * character argument, (expressed as an int), returning WEOF in
53 * the event that conversion fails.
57 if( __mingw_mbtowc_convert( (char *)(&c), 1, &wc_result, 1) == 1 )
63 wint_t __mingw_btowc( int c )
64 { /* Wrapper for the btowc() function; this will unconditionally
65 * delegate the call to the MinGW fallback implementation, (as
66 * implemented above), after initialization of the effective
67 * codeset file-global variable.
69 (void)(__mingw_mbrtowc_codeset_init());
70 return __mingw_btowc_fallback( c );
73 wint_t __msvcrt_btowc( int c )
74 { /* Wrapper for the btowc() function; it will initially attempt
75 * to delegate the call to a Microsoft-provided implementation,
76 * but if no such implementation can be found, fall back to the
77 * MinGW substitute (defined above).
79 static wint_t (*redirector_hook)( int ) = NULL;
81 /* MSVCRT.DLL's setlocale() cannot reliably handle code pages with
82 * more than two bytes per code point, (e.g. UTF-7 and UTF-8); thus,
83 * Microsoft's btowc() is likely to be similarly unreliable, so we
84 * always use the MinGW fallback with such code pages.
86 if( __mb_cur_max_for_codeset(__mingw_mbrtowc_codeset_init()) > 2 )
87 return __mingw_btowc_fallback( c );
89 /* On first time call, we don't know which implementation is to be
90 * selected; look for a Microsoft implementation, which, if available,
91 * may be registered for immediate use on this, and any subsequent,
92 * calls to this function wrapper...
94 if( (redirector_hook == NULL)
95 && ((redirector_hook = dlsym( RTLD_DEFAULT, "btowc" )) == NULL) )
97 /* ...but when no Microsoft implementation can be found, register
98 * the MinGW fall back in its stead.
100 redirector_hook = __mingw_btowc_fallback;
102 /* Finally, delegate the call to whichever implementation has been
103 * registered on first-time call.
105 return redirector_hook( c );
108 /* $RCSfile$: end of file */