lib/c++defs.h

   1 /* C++ compatible function declaration macros.
   2    Copyright (C) 2010-2024 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_EXTERN_C_FUNC declaration;
  97    performs the declaration of a function with C linkage.  */
  98 #if defined __cplusplus
  99 # define _GL_EXTERN_C_FUNC extern "C"
 100 #else
 101 /* In C mode, omit the 'extern' keyword, because attributes in bracket syntax
 102    are not allowed between 'extern' and the return type (see gnulib-common.m4).
 103  */
 104 # define _GL_EXTERN_C_FUNC
 105 #endif
 106
 107 /* _GL_FUNCDECL_RPL (func, rettype, parameters[, attributes]);
 108    declares a replacement function, named rpl_func, with the given prototype,
 109    consisting of return type, parameters, and attributes.
 110    Example:
 111      _GL_FUNCDECL_RPL (open, int, (const char *filename, int flags, ...),
 112                                   _GL_ARG_NONNULL ((1)));
 113
 114    Note: Attributes, such as _GL_ATTRIBUTE_DEPRECATED, are supported in front
 115    of a _GL_FUNCDECL_RPL invocation only in C mode, not in C++ mode.  (That's
 116    because
 117      [[...]] extern "C" <declaration>;
 118    is invalid syntax in C++.)
 119
 120    Note: The attribute _GL_ATTRIBUTE_NOTHROW, if needed, must be placed outside
 121    of the _GL_FUNCDECL_RPL invocation, at the end of the declaration.
 122  */
 123 #define _GL_FUNCDECL_RPL(func,rettype,parameters,...) \
 124   _GL_FUNCDECL_RPL_1 (rpl_##func, rettype, parameters, __VA_ARGS__)
 125 #define _GL_FUNCDECL_RPL_1(rpl_func,rettype,parameters,...) \
 126   _GL_EXTERN_C_FUNC __VA_ARGS__ rettype rpl_func parameters
 127
 128 /* _GL_FUNCDECL_SYS (func, rettype, parameters[, attributes]);
 129    declares the system function, named func, with the given prototype,
 130    consisting of return type, parameters, and attributes.
 131    Example:
 132      _GL_FUNCDECL_SYS (open, int, (const char *filename, int flags, ...),
 133                                   _GL_ARG_NONNULL ((1)));
 134
 135    Note: The attribute _GL_ATTRIBUTE_NOTHROW, if needed, must be placed outside
 136    of the _GL_FUNCDECL_SYS invocation, at the end of the declaration.
 137  */
 138 #define _GL_FUNCDECL_SYS(func,rettype,parameters,...) \
 139   _GL_EXTERN_C_FUNC __VA_ARGS__ rettype func parameters
 140
 141 /* _GL_CXXALIAS_RPL (func, rettype, parameters);
 142    declares a C++ alias called GNULIB_NAMESPACE::func
 143    that redirects to rpl_func, if GNULIB_NAMESPACE is defined.
 144    Example:
 145      _GL_CXXALIAS_RPL (open, int, (const char *filename, int flags, ...));
 146
 147    Wrapping rpl_func in an object with an inline conversion operator
 148    avoids a reference to rpl_func unless GNULIB_NAMESPACE::func is
 149    actually used in the program.  */
 150 #define _GL_CXXALIAS_RPL(func,rettype,parameters) \
 151   _GL_CXXALIAS_RPL_1 (func, rpl_##func, rettype, parameters)
 152 #if defined __cplusplus && defined GNULIB_NAMESPACE
 153 # define _GL_CXXALIAS_RPL_1(func,rpl_func,rettype,parameters) \
 154     namespace GNULIB_NAMESPACE                                \
 155     {                                                         \
 156       static const struct _gl_ ## func ## _wrapper            \
 157       {                                                       \
 158         typedef rettype (*type) parameters;                   \
 159                                                               \
 160         inline operator type () const                         \
 161         {                                                     \
 162           return ::rpl_func;                                  \
 163         }                                                     \
 164       } func = {};                                            \
 165     }                                                         \
 166     _GL_EXTERN_C int _gl_cxxalias_dummy
 167 #else
 168 # define _GL_CXXALIAS_RPL_1(func,rpl_func,rettype,parameters) \
 169     _GL_EXTERN_C int _gl_cxxalias_dummy
 170 #endif
 171
 172 /* _GL_CXXALIAS_MDA (func, rettype, parameters);
 173    is to be used when func is a Microsoft deprecated alias, on native Windows.
 174    It declares a C++ alias called GNULIB_NAMESPACE::func
 175    that redirects to _func, if GNULIB_NAMESPACE is defined.
 176    Example:
 177      _GL_CXXALIAS_MDA (open, int, (const char *filename, int flags, ...));
 178  */
 179 #define _GL_CXXALIAS_MDA(func,rettype,parameters) \
 180   _GL_CXXALIAS_RPL_1 (func, _##func, rettype, parameters)
 181
 182 /* _GL_CXXALIAS_RPL_CAST_1 (func, rpl_func, rettype, parameters);
 183    is like  _GL_CXXALIAS_RPL_1 (func, rpl_func, rettype, parameters);
 184    except that the C function rpl_func may have a slightly different
 185    declaration.  A cast is used to silence the "invalid conversion" error
 186    that would otherwise occur.  */
 187 #if defined __cplusplus && defined GNULIB_NAMESPACE
 188 # define _GL_CXXALIAS_RPL_CAST_1(func,rpl_func,rettype,parameters) \
 189     namespace GNULIB_NAMESPACE                                     \
 190     {                                                              \
 191       static const struct _gl_ ## func ## _wrapper                 \
 192       {                                                            \
 193         typedef rettype (*type) parameters;                        \
 194                                                                    \
 195         inline operator type () const                              \
 196         {                                                          \
 197           return reinterpret_cast<type>(::rpl_func);               \
 198         }                                                          \
 199       } func = {};                                                 \
 200     }                                                              \
 201     _GL_EXTERN_C int _gl_cxxalias_dummy
 202 #else
 203 # define _GL_CXXALIAS_RPL_CAST_1(func,rpl_func,rettype,parameters) \
 204     _GL_EXTERN_C int _gl_cxxalias_dummy
 205 #endif
 206
 207 /* _GL_CXXALIAS_MDA_CAST (func, rettype, parameters);
 208    is like  _GL_CXXALIAS_MDA (func, rettype, parameters);
 209    except that the C function func may have a slightly different declaration.
 210    A cast is used to silence the "invalid conversion" error that would
 211    otherwise occur.  */
 212 #define _GL_CXXALIAS_MDA_CAST(func,rettype,parameters) \
 213   _GL_CXXALIAS_RPL_CAST_1 (func, _##func, rettype, parameters)
 214
 215 /* _GL_CXXALIAS_SYS (func, rettype, parameters);
 216    declares a C++ alias called GNULIB_NAMESPACE::func
 217    that redirects to the system provided function func, if GNULIB_NAMESPACE
 218    is defined.
 219    Example:
 220      _GL_CXXALIAS_SYS (open, int, (const char *filename, int flags, ...));
 221
 222    Wrapping func in an object with an inline conversion operator
 223    avoids a reference to func unless GNULIB_NAMESPACE::func is
 224    actually used in the program.  */
 225 #if defined __cplusplus && defined GNULIB_NAMESPACE
 226 # define _GL_CXXALIAS_SYS(func,rettype,parameters)            \
 227     namespace GNULIB_NAMESPACE                                \
 228     {                                                         \
 229       static const struct _gl_ ## func ## _wrapper            \
 230       {                                                       \
 231         typedef rettype (*type) parameters;                   \
 232                                                               \
 233         inline operator type () const                         \
 234         {                                                     \
 235           return ::func;                                      \
 236         }                                                     \
 237       } func = {};                                            \
 238     }                                                         \
 239     _GL_EXTERN_C int _gl_cxxalias_dummy
 240 #else
 241 # define _GL_CXXALIAS_SYS(func,rettype,parameters) \
 242     _GL_EXTERN_C int _gl_cxxalias_dummy
 243 #endif
 244
 245 /* _GL_CXXALIAS_SYS_CAST (func, rettype, parameters);
 246    is like  _GL_CXXALIAS_SYS (func, rettype, parameters);
 247    except that the C function func may have a slightly different declaration.
 248    A cast is used to silence the "invalid conversion" error that would
 249    otherwise occur.  */
 250 #if defined __cplusplus && defined GNULIB_NAMESPACE
 251 # define _GL_CXXALIAS_SYS_CAST(func,rettype,parameters) \
 252     namespace GNULIB_NAMESPACE                          \
 253     {                                                   \
 254       static const struct _gl_ ## func ## _wrapper      \
 255       {                                                 \
 256         typedef rettype (*type) parameters;             \
 257                                                         \
 258         inline operator type () const                   \
 259         {                                               \
 260           return reinterpret_cast<type>(::func);        \
 261         }                                               \
 262       } func = {};                                      \
 263     }                                                   \
 264     _GL_EXTERN_C int _gl_cxxalias_dummy
 265 #else
 266 # define _GL_CXXALIAS_SYS_CAST(func,rettype,parameters) \
 267     _GL_EXTERN_C int _gl_cxxalias_dummy
 268 #endif
 269
 270 /* _GL_CXXALIAS_SYS_CAST2 (func, rettype, parameters, rettype2, parameters2);
 271    is like  _GL_CXXALIAS_SYS (func, rettype, parameters);
 272    except that the C function is picked among a set of overloaded functions,
 273    namely the one with rettype2 and parameters2.  Two consecutive casts
 274    are used to silence the "cannot find a match" and "invalid conversion"
 275    errors that would otherwise occur.  */
 276 #if defined __cplusplus && defined GNULIB_NAMESPACE
 277   /* The outer cast must be a reinterpret_cast.
 278      The inner cast: When the function is defined as a set of overloaded
 279      functions, it works as a static_cast<>, choosing the designated variant.
 280      When the function is defined as a single variant, it works as a
 281      reinterpret_cast<>. The parenthesized cast syntax works both ways.  */
 282 # define _GL_CXXALIAS_SYS_CAST2(func,rettype,parameters,rettype2,parameters2) \
 283     namespace GNULIB_NAMESPACE                                                \
 284     {                                                                         \
 285       static const struct _gl_ ## func ## _wrapper                            \
 286       {                                                                       \
 287         typedef rettype (*type) parameters;                                   \
 288                                                                               \
 289         inline operator type () const                                         \
 290         {                                                                     \
 291           return reinterpret_cast<type>((rettype2 (*) parameters2)(::func));  \
 292         }                                                                     \
 293       } func = {};                                                            \
 294     }                                                                         \
 295     _GL_EXTERN_C int _gl_cxxalias_dummy
 296 #else
 297 # define _GL_CXXALIAS_SYS_CAST2(func,rettype,parameters,rettype2,parameters2) \
 298     _GL_EXTERN_C int _gl_cxxalias_dummy
 299 #endif
 300
 301 /* _GL_CXXALIASWARN (func);
 302    causes a warning to be emitted when ::func is used but not when
 303    GNULIB_NAMESPACE::func is used.  func must be defined without overloaded
 304    variants.  */
 305 #if defined __cplusplus && defined GNULIB_NAMESPACE
 306 # define _GL_CXXALIASWARN(func) \
 307    _GL_CXXALIASWARN_1 (func, GNULIB_NAMESPACE)
 308 # define _GL_CXXALIASWARN_1(func,namespace) \
 309    _GL_CXXALIASWARN_2 (func, namespace)
 310 /* To work around GCC bug <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43881>,
 311    we enable the warning only when not optimizing.  */
 312 # if !(defined __GNUC__ && !defined __clang__ && __OPTIMIZE__)
 313 #  define _GL_CXXALIASWARN_2(func,namespace) \
 314     _GL_WARN_ON_USE (func, \
 315                      "The symbol ::" #func " refers to the system function. " \
 316                      "Use " #namespace "::" #func " instead.")
 317 # elif (__GNUC__ >= 3 || defined __clang__) && GNULIB_STRICT_CHECKING
 318 #  define _GL_CXXALIASWARN_2(func,namespace) \
 319      extern __typeof__ (func) func
 320 # else
 321 #  define _GL_CXXALIASWARN_2(func,namespace) \
 322      _GL_EXTERN_C int _gl_cxxalias_dummy
 323 # endif
 324 #else
 325 # define _GL_CXXALIASWARN(func) \
 326     _GL_EXTERN_C int _gl_cxxalias_dummy
 327 #endif
 328
 329 /* _GL_CXXALIASWARN1 (func, rettype, parameters_and_attributes);
 330    causes a warning to be emitted when the given overloaded variant of ::func
 331    is used but not when GNULIB_NAMESPACE::func is used.  */
 332 #if defined __cplusplus && defined GNULIB_NAMESPACE
 333 # define _GL_CXXALIASWARN1(func,rettype,parameters_and_attributes) \
 334    _GL_CXXALIASWARN1_1 (func, rettype, parameters_and_attributes, \
 335                         GNULIB_NAMESPACE)
 336 # define _GL_CXXALIASWARN1_1(func,rettype,parameters_and_attributes,namespace) \
 337    _GL_CXXALIASWARN1_2 (func, rettype, parameters_and_attributes, namespace)
 338 /* To work around GCC bug <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43881>,
 339    we enable the warning only when not optimizing.  */
 340 # if !(defined __GNUC__ && !defined __clang__ && __OPTIMIZE__)
 341 #  define _GL_CXXALIASWARN1_2(func,rettype,parameters_and_attributes,namespace) \
 342     _GL_WARN_ON_USE_CXX (func, rettype, rettype, parameters_and_attributes, \
 343                          "The symbol ::" #func " refers to the system function. " \
 344                          "Use " #namespace "::" #func " instead.")
 345 # else
 346 #  define _GL_CXXALIASWARN1_2(func,rettype,parameters_and_attributes,namespace) \
 347      _GL_EXTERN_C int _gl_cxxalias_dummy
 348 # endif
 349 #else
 350 # define _GL_CXXALIASWARN1(func,rettype,parameters_and_attributes) \
 351     _GL_EXTERN_C int _gl_cxxalias_dummy
 352 #endif
 353
 354 #endif /* _GL_CXXDEFS_H */