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 <limits.h>, for UCHAR_MAX, and <stdio.h>, for EOF.
49 /* We need to look up the effective working codeset, before choosing
50 * between MSVCRT.DLL and MinGW fallback implementations; to avoid a
51 * need to look it up again, within the MinGW fallback, we store the
52 * result of the initial look up in this file-global variable.
54 static __thread unsigned int cs;
56 static wint_t __mingw_btowc_fallback( int c )
58 /* Fallback function, providing an implementation of the btowc()
59 * function, when none is available within the Microsoft runtime.
60 * This performs an MBCS to wchar_t conversion on the given single
61 * character argument, (expressed as an int), returning WEOF in
62 * the event that conversion fails.
67 { if( (cs == 0) && (UCHAR_MAX >= (unsigned int)(c)) ) return (wchar_t)(c);
68 MultiByteToWideChar( cs, MB_ERR_INVALID_CHARS, (char *)(&c), 1, &wc, 1 );
73 wint_t __mingw_btowc( int c )
75 /* Wrapper for the btowc() function; this will unconditionally
76 * delegate the call to the MinGW fallback implementation, (as
77 * implemented above), after initialization of the effective
78 * codeset file-global variable.
80 cs = __mb_codeset_for_locale();
81 return __mingw_btowc_fallback( c );
84 wint_t __msvcrt_btowc( int c )
86 /* Wrapper for the btowc() function; it will initially attempt
87 * to delegate the call to a Microsoft-provided implementation,
88 * but if no such implementation can be found, fall back to the
89 * MinGW substitute (defined above).
91 static wint_t (*redirector_hook)( int ) = NULL;
93 /* MSVCRT.DLL's setlocale() cannot reliably handle code pages with
94 * more than two bytes per code point, (e.g. UTF-7 and UTF-8); thus,
95 * Microsoft's btowc() is likely to be similarly unreliable, so we
96 * always use the MinGW fallback with such code pages.
98 if( __mb_cur_max_for_codeset( cs = __mb_codeset_for_locale() ) > 2 )
99 return __mingw_btowc_fallback( c );
101 /* On first time call, we don't know which implementation is to be
102 * selected; look for a Microsoft implementation, which, if available,
103 * may be registered for immediate use on this, and any subsequent,
104 * calls to this function wrapper...
106 if( (redirector_hook == NULL)
107 && ((redirector_hook = dlsym( RTLD_DEFAULT, "btowc" )) == NULL) )
109 /* ...but when no Microsoft implementation can be found, register
110 * the MinGW fall back in its stead.
112 redirector_hook = __mingw_btowc_fallback;
114 /* Finally, delegate the call to whichever implementation has been
115 * registered on first-time call.
117 return redirector_hook( c );
120 /* $RCSfile$: end of file */