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c++defs.h
1 /* C++ compatible function declaration macros.
2  Copyright (C) 2010-2023 Free Software Foundation, Inc.
3 
4  This program is free software: you can redistribute it and/or modify it
5  under the terms of the GNU Lesser General Public License as published
6  by the Free Software Foundation; either version 2 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 GNU
12  Lesser General Public License for more details.
13 
14  You should have received a copy of the GNU Lesser General Public License
15  along with this program. If not, see <https://www.gnu.org/licenses/>. */
16 
17 #ifndef _GL_CXXDEFS_H
18 #define _GL_CXXDEFS_H
19 
20 /* Begin/end the GNULIB_NAMESPACE namespace. */
21 #if defined __cplusplus && defined GNULIB_NAMESPACE
22 # define _GL_BEGIN_NAMESPACE namespace GNULIB_NAMESPACE {
23 # define _GL_END_NAMESPACE }
24 #else
25 # define _GL_BEGIN_NAMESPACE
26 # define _GL_END_NAMESPACE
27 #endif
28 
29 /* The three most frequent use cases of these macros are:
30 
31  * For providing a substitute for a function that is missing on some
32  platforms, but is declared and works fine on the platforms on which
33  it exists:
34 
35  #if @GNULIB_FOO@
36  # if !@HAVE_FOO@
37  _GL_FUNCDECL_SYS (foo, ...);
38  # endif
39  _GL_CXXALIAS_SYS (foo, ...);
40  _GL_CXXALIASWARN (foo);
41  #elif defined GNULIB_POSIXCHECK
42  ...
43  #endif
44 
45  * For providing a replacement for a function that exists on all platforms,
46  but is broken/insufficient and needs to be replaced on some platforms:
47 
48  #if @GNULIB_FOO@
49  # if @REPLACE_FOO@
50  # if !(defined __cplusplus && defined GNULIB_NAMESPACE)
51  # undef foo
52  # define foo rpl_foo
53  # endif
54  _GL_FUNCDECL_RPL (foo, ...);
55  _GL_CXXALIAS_RPL (foo, ...);
56  # else
57  _GL_CXXALIAS_SYS (foo, ...);
58  # endif
59  _GL_CXXALIASWARN (foo);
60  #elif defined GNULIB_POSIXCHECK
61  ...
62  #endif
63 
64  * For providing a replacement for a function that exists on some platforms
65  but is broken/insufficient and needs to be replaced on some of them and
66  is additionally either missing or undeclared on some other platforms:
67 
68  #if @GNULIB_FOO@
69  # if @REPLACE_FOO@
70  # if !(defined __cplusplus && defined GNULIB_NAMESPACE)
71  # undef foo
72  # define foo rpl_foo
73  # endif
74  _GL_FUNCDECL_RPL (foo, ...);
75  _GL_CXXALIAS_RPL (foo, ...);
76  # else
77  # if !@HAVE_FOO@ or if !@HAVE_DECL_FOO@
78  _GL_FUNCDECL_SYS (foo, ...);
79  # endif
80  _GL_CXXALIAS_SYS (foo, ...);
81  # endif
82  _GL_CXXALIASWARN (foo);
83  #elif defined GNULIB_POSIXCHECK
84  ...
85  #endif
86 */
87 
88 /* _GL_EXTERN_C declaration;
89  performs the declaration with C linkage. */
90 #if defined __cplusplus
91 # define _GL_EXTERN_C extern "C"
92 #else
93 # define _GL_EXTERN_C extern
94 #endif
95 
96 /* _GL_FUNCDECL_RPL (func, rettype, parameters_and_attributes);
97  declares a replacement function, named rpl_func, with the given prototype,
98  consisting of return type, parameters, and attributes.
99  Example:
100  _GL_FUNCDECL_RPL (open, int, (const char *filename, int flags, ...)
101  _GL_ARG_NONNULL ((1)));
102 
103  Note: Attributes, such as _GL_ATTRIBUTE_DEPRECATED, are supported in front
104  of a _GL_FUNCDECL_RPL invocation only in C mode, not in C++ mode. (That's
105  because
106  [[...]] extern "C" <declaration>;
107  is invalid syntax in C++.)
108  */
109 #define _GL_FUNCDECL_RPL(func,rettype,parameters_and_attributes) \
110  _GL_FUNCDECL_RPL_1 (rpl_##func, rettype, parameters_and_attributes)
111 #define _GL_FUNCDECL_RPL_1(rpl_func,rettype,parameters_and_attributes) \
112  _GL_EXTERN_C rettype rpl_func parameters_and_attributes
113 
114 /* _GL_FUNCDECL_SYS (func, rettype, parameters_and_attributes);
115  declares the system function, named func, with the given prototype,
116  consisting of return type, parameters, and attributes.
117  Example:
118  _GL_FUNCDECL_SYS (open, int, (const char *filename, int flags, ...)
119  _GL_ARG_NONNULL ((1)));
120  */
121 #define _GL_FUNCDECL_SYS(func,rettype,parameters_and_attributes) \
122  _GL_EXTERN_C rettype func parameters_and_attributes
123 
124 /* _GL_CXXALIAS_RPL (func, rettype, parameters);
125  declares a C++ alias called GNULIB_NAMESPACE::func
126  that redirects to rpl_func, if GNULIB_NAMESPACE is defined.
127  Example:
128  _GL_CXXALIAS_RPL (open, int, (const char *filename, int flags, ...));
129 
130  Wrapping rpl_func in an object with an inline conversion operator
131  avoids a reference to rpl_func unless GNULIB_NAMESPACE::func is
132  actually used in the program. */
133 #define _GL_CXXALIAS_RPL(func,rettype,parameters) \
134  _GL_CXXALIAS_RPL_1 (func, rpl_##func, rettype, parameters)
135 #if defined __cplusplus && defined GNULIB_NAMESPACE
136 # define _GL_CXXALIAS_RPL_1(func,rpl_func,rettype,parameters) \
137  namespace GNULIB_NAMESPACE \
138  { \
139  static const struct _gl_ ## func ## _wrapper \
140  { \
141  typedef rettype (*type) parameters; \
142  \
143  inline operator type () const \
144  { \
145  return ::rpl_func; \
146  } \
147  } func = {}; \
148  } \
149  _GL_EXTERN_C int _gl_cxxalias_dummy
150 #else
151 # define _GL_CXXALIAS_RPL_1(func,rpl_func,rettype,parameters) \
152  _GL_EXTERN_C int _gl_cxxalias_dummy
153 #endif
154 
155 /* _GL_CXXALIAS_MDA (func, rettype, parameters);
156  is to be used when func is a Microsoft deprecated alias, on native Windows.
157  It declares a C++ alias called GNULIB_NAMESPACE::func
158  that redirects to _func, if GNULIB_NAMESPACE is defined.
159  Example:
160  _GL_CXXALIAS_MDA (open, int, (const char *filename, int flags, ...));
161  */
162 #define _GL_CXXALIAS_MDA(func,rettype,parameters) \
163  _GL_CXXALIAS_RPL_1 (func, _##func, rettype, parameters)
164 
165 /* _GL_CXXALIAS_RPL_CAST_1 (func, rpl_func, rettype, parameters);
166  is like _GL_CXXALIAS_RPL_1 (func, rpl_func, rettype, parameters);
167  except that the C function rpl_func may have a slightly different
168  declaration. A cast is used to silence the "invalid conversion" error
169  that would otherwise occur. */
170 #if defined __cplusplus && defined GNULIB_NAMESPACE
171 # define _GL_CXXALIAS_RPL_CAST_1(func,rpl_func,rettype,parameters) \
172  namespace GNULIB_NAMESPACE \
173  { \
174  static const struct _gl_ ## func ## _wrapper \
175  { \
176  typedef rettype (*type) parameters; \
177  \
178  inline operator type () const \
179  { \
180  return reinterpret_cast<type>(::rpl_func); \
181  } \
182  } func = {}; \
183  } \
184  _GL_EXTERN_C int _gl_cxxalias_dummy
185 #else
186 # define _GL_CXXALIAS_RPL_CAST_1(func,rpl_func,rettype,parameters) \
187  _GL_EXTERN_C int _gl_cxxalias_dummy
188 #endif
189 
190 /* _GL_CXXALIAS_MDA_CAST (func, rettype, parameters);
191  is like _GL_CXXALIAS_MDA (func, rettype, parameters);
192  except that the C function func may have a slightly different declaration.
193  A cast is used to silence the "invalid conversion" error that would
194  otherwise occur. */
195 #define _GL_CXXALIAS_MDA_CAST(func,rettype,parameters) \
196  _GL_CXXALIAS_RPL_CAST_1 (func, _##func, rettype, parameters)
197 
198 /* _GL_CXXALIAS_SYS (func, rettype, parameters);
199  declares a C++ alias called GNULIB_NAMESPACE::func
200  that redirects to the system provided function func, if GNULIB_NAMESPACE
201  is defined.
202  Example:
203  _GL_CXXALIAS_SYS (open, int, (const char *filename, int flags, ...));
204 
205  Wrapping func in an object with an inline conversion operator
206  avoids a reference to func unless GNULIB_NAMESPACE::func is
207  actually used in the program. */
208 #if defined __cplusplus && defined GNULIB_NAMESPACE
209 # define _GL_CXXALIAS_SYS(func,rettype,parameters) \
210  namespace GNULIB_NAMESPACE \
211  { \
212  static const struct _gl_ ## func ## _wrapper \
213  { \
214  typedef rettype (*type) parameters; \
215  \
216  inline operator type () const \
217  { \
218  return ::func; \
219  } \
220  } func = {}; \
221  } \
222  _GL_EXTERN_C int _gl_cxxalias_dummy
223 #else
224 # define _GL_CXXALIAS_SYS(func,rettype,parameters) \
225  _GL_EXTERN_C int _gl_cxxalias_dummy
226 #endif
227 
228 /* _GL_CXXALIAS_SYS_CAST (func, rettype, parameters);
229  is like _GL_CXXALIAS_SYS (func, rettype, parameters);
230  except that the C function func may have a slightly different declaration.
231  A cast is used to silence the "invalid conversion" error that would
232  otherwise occur. */
233 #if defined __cplusplus && defined GNULIB_NAMESPACE
234 # define _GL_CXXALIAS_SYS_CAST(func,rettype,parameters) \
235  namespace GNULIB_NAMESPACE \
236  { \
237  static const struct _gl_ ## func ## _wrapper \
238  { \
239  typedef rettype (*type) parameters; \
240  \
241  inline operator type () const \
242  { \
243  return reinterpret_cast<type>(::func); \
244  } \
245  } func = {}; \
246  } \
247  _GL_EXTERN_C int _gl_cxxalias_dummy
248 #else
249 # define _GL_CXXALIAS_SYS_CAST(func,rettype,parameters) \
250  _GL_EXTERN_C int _gl_cxxalias_dummy
251 #endif
252 
253 /* _GL_CXXALIAS_SYS_CAST2 (func, rettype, parameters, rettype2, parameters2);
254  is like _GL_CXXALIAS_SYS (func, rettype, parameters);
255  except that the C function is picked among a set of overloaded functions,
256  namely the one with rettype2 and parameters2. Two consecutive casts
257  are used to silence the "cannot find a match" and "invalid conversion"
258  errors that would otherwise occur. */
259 #if defined __cplusplus && defined GNULIB_NAMESPACE
260  /* The outer cast must be a reinterpret_cast.
261  The inner cast: When the function is defined as a set of overloaded
262  functions, it works as a static_cast<>, choosing the designated variant.
263  When the function is defined as a single variant, it works as a
264  reinterpret_cast<>. The parenthesized cast syntax works both ways. */
265 # define _GL_CXXALIAS_SYS_CAST2(func,rettype,parameters,rettype2,parameters2) \
266  namespace GNULIB_NAMESPACE \
267  { \
268  static const struct _gl_ ## func ## _wrapper \
269  { \
270  typedef rettype (*type) parameters; \
271  \
272  inline operator type () const \
273  { \
274  return reinterpret_cast<type>((rettype2 (*) parameters2)(::func)); \
275  } \
276  } func = {}; \
277  } \
278  _GL_EXTERN_C int _gl_cxxalias_dummy
279 #else
280 # define _GL_CXXALIAS_SYS_CAST2(func,rettype,parameters,rettype2,parameters2) \
281  _GL_EXTERN_C int _gl_cxxalias_dummy
282 #endif
283 
284 /* _GL_CXXALIASWARN (func);
285  causes a warning to be emitted when ::func is used but not when
286  GNULIB_NAMESPACE::func is used. func must be defined without overloaded
287  variants. */
288 #if defined __cplusplus && defined GNULIB_NAMESPACE
289 # define _GL_CXXALIASWARN(func) \
290  _GL_CXXALIASWARN_1 (func, GNULIB_NAMESPACE)
291 # define _GL_CXXALIASWARN_1(func,namespace) \
292  _GL_CXXALIASWARN_2 (func, namespace)
293 /* To work around GCC bug <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43881>,
294  we enable the warning only when not optimizing. */
295 # if !(defined __GNUC__ && !defined __clang__ && __OPTIMIZE__)
296 # define _GL_CXXALIASWARN_2(func,namespace) \
297  _GL_WARN_ON_USE (func, \
298  "The symbol ::" #func " refers to the system function. " \
299  "Use " #namespace "::" #func " instead.")
300 # elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING
301 # define _GL_CXXALIASWARN_2(func,namespace) \
302  extern __typeof__ (func) func
303 # else
304 # define _GL_CXXALIASWARN_2(func,namespace) \
305  _GL_EXTERN_C int _gl_cxxalias_dummy
306 # endif
307 #else
308 # define _GL_CXXALIASWARN(func) \
309  _GL_EXTERN_C int _gl_cxxalias_dummy
310 #endif
311 
312 /* _GL_CXXALIASWARN1 (func, rettype, parameters_and_attributes);
313  causes a warning to be emitted when the given overloaded variant of ::func
314  is used but not when GNULIB_NAMESPACE::func is used. */
315 #if defined __cplusplus && defined GNULIB_NAMESPACE
316 # define _GL_CXXALIASWARN1(func,rettype,parameters_and_attributes) \
317  _GL_CXXALIASWARN1_1 (func, rettype, parameters_and_attributes, \
318  GNULIB_NAMESPACE)
319 # define _GL_CXXALIASWARN1_1(func,rettype,parameters_and_attributes,namespace) \
320  _GL_CXXALIASWARN1_2 (func, rettype, parameters_and_attributes, namespace)
321 /* To work around GCC bug <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43881>,
322  we enable the warning only when not optimizing. */
323 # if !(defined __GNUC__ && !defined __clang__ && __OPTIMIZE__)
324 # define _GL_CXXALIASWARN1_2(func,rettype,parameters_and_attributes,namespace) \
325  _GL_WARN_ON_USE_CXX (func, rettype, rettype, parameters_and_attributes, \
326  "The symbol ::" #func " refers to the system function. " \
327  "Use " #namespace "::" #func " instead.")
328 # else
329 # define _GL_CXXALIASWARN1_2(func,rettype,parameters_and_attributes,namespace) \
330  _GL_EXTERN_C int _gl_cxxalias_dummy
331 # endif
332 #else
333 # define _GL_CXXALIASWARN1(func,rettype,parameters_and_attributes) \
334  _GL_EXTERN_C int _gl_cxxalias_dummy
335 #endif
336 
337 #endif /* _GL_CXXDEFS_H */