lib/c++defs.h

   1 /* C++ compatible function declaration macros.
   2    Copyright (C) 2010-2020 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 #define _GL_FUNCDECL_RPL(func,rettype,parameters_and_attributes) \
 104   _GL_FUNCDECL_RPL_1 (rpl_##func, rettype, parameters_and_attributes)
 105 #define _GL_FUNCDECL_RPL_1(rpl_func,rettype,parameters_and_attributes) \
 106   _GL_EXTERN_C rettype rpl_func parameters_and_attributes
 107
 108 /* _GL_FUNCDECL_SYS (func, rettype, parameters_and_attributes);
 109    declares the system function, named func, with the given prototype,
 110    consisting of return type, parameters, and attributes.
 111    Example:
 112      _GL_FUNCDECL_SYS (open, int, (const char *filename, int flags, ...)
 113                                   _GL_ARG_NONNULL ((1)));
 114  */
 115 #define _GL_FUNCDECL_SYS(func,rettype,parameters_and_attributes) \
 116   _GL_EXTERN_C rettype func parameters_and_attributes
 117
 118 /* _GL_CXXALIAS_RPL (func, rettype, parameters);
 119    declares a C++ alias called GNULIB_NAMESPACE::func
 120    that redirects to rpl_func, if GNULIB_NAMESPACE is defined.
 121    Example:
 122      _GL_CXXALIAS_RPL (open, int, (const char *filename, int flags, ...));
 123
 124    Wrapping rpl_func in an object with an inline conversion operator
 125    avoids a reference to rpl_func unless GNULIB_NAMESPACE::func is
 126    actually used in the program.  */
 127 #define _GL_CXXALIAS_RPL(func,rettype,parameters) \
 128   _GL_CXXALIAS_RPL_1 (func, rpl_##func, rettype, parameters)
 129 #if defined __cplusplus && defined GNULIB_NAMESPACE
 130 # define _GL_CXXALIAS_RPL_1(func,rpl_func,rettype,parameters) \
 131     namespace GNULIB_NAMESPACE                                \
 132     {                                                         \
 133       static const struct _gl_ ## func ## _wrapper            \
 134       {                                                       \
 135         typedef rettype (*type) parameters;                   \
 136                                                               \
 137         inline operator type () const                         \
 138         {                                                     \
 139           return ::rpl_func;                                  \
 140         }                                                     \
 141       } func = {};                                            \
 142     }                                                         \
 143     _GL_EXTERN_C int _gl_cxxalias_dummy
 144 #else
 145 # define _GL_CXXALIAS_RPL_1(func,rpl_func,rettype,parameters) \
 146     _GL_EXTERN_C int _gl_cxxalias_dummy
 147 #endif
 148
 149 /* _GL_CXXALIAS_MDA (func, rettype, parameters);
 150    is to be used when func is a Microsoft deprecated alias, on native Windows.
 151    It declares a C++ alias called GNULIB_NAMESPACE::func
 152    that redirects to _func, if GNULIB_NAMESPACE is defined.
 153    Example:
 154      _GL_CXXALIAS_MDA (open, int, (const char *filename, int flags, ...));
 155  */
 156 #define _GL_CXXALIAS_MDA(func,rettype,parameters) \
 157   _GL_CXXALIAS_RPL_1 (func, _##func, rettype, parameters)
 158
 159 /* _GL_CXXALIAS_RPL_CAST_1 (func, rpl_func, rettype, parameters);
 160    is like  _GL_CXXALIAS_RPL_1 (func, rpl_func, rettype, parameters);
 161    except that the C function rpl_func may have a slightly different
 162    declaration.  A cast is used to silence the "invalid conversion" error
 163    that would otherwise occur.  */
 164 #if defined __cplusplus && defined GNULIB_NAMESPACE
 165 # define _GL_CXXALIAS_RPL_CAST_1(func,rpl_func,rettype,parameters) \
 166     namespace GNULIB_NAMESPACE                                     \
 167     {                                                              \
 168       static const struct _gl_ ## func ## _wrapper                 \
 169       {                                                            \
 170         typedef rettype (*type) parameters;                        \
 171                                                                    \
 172         inline operator type () const                              \
 173         {                                                          \
 174           return reinterpret_cast<type>(::rpl_func);               \
 175         }                                                          \
 176       } func = {};                                                 \
 177     }                                                              \
 178     _GL_EXTERN_C int _gl_cxxalias_dummy
 179 #else
 180 # define _GL_CXXALIAS_RPL_CAST_1(func,rpl_func,rettype,parameters) \
 181     _GL_EXTERN_C int _gl_cxxalias_dummy
 182 #endif
 183
 184 /* _GL_CXXALIAS_SYS (func, rettype, parameters);
 185    declares a C++ alias called GNULIB_NAMESPACE::func
 186    that redirects to the system provided function func, if GNULIB_NAMESPACE
 187    is defined.
 188    Example:
 189      _GL_CXXALIAS_SYS (open, int, (const char *filename, int flags, ...));
 190
 191    Wrapping func in an object with an inline conversion operator
 192    avoids a reference to func unless GNULIB_NAMESPACE::func is
 193    actually used in the program.  */
 194 #if defined __cplusplus && defined GNULIB_NAMESPACE
 195 # define _GL_CXXALIAS_SYS(func,rettype,parameters)            \
 196     namespace GNULIB_NAMESPACE                                \
 197     {                                                         \
 198       static const struct _gl_ ## func ## _wrapper            \
 199       {                                                       \
 200         typedef rettype (*type) parameters;                   \
 201                                                               \
 202         inline operator type () const                         \
 203         {                                                     \
 204           return ::func;                                      \
 205         }                                                     \
 206       } func = {};                                            \
 207     }                                                         \
 208     _GL_EXTERN_C int _gl_cxxalias_dummy
 209 #else
 210 # define _GL_CXXALIAS_SYS(func,rettype,parameters) \
 211     _GL_EXTERN_C int _gl_cxxalias_dummy
 212 #endif
 213
 214 /* _GL_CXXALIAS_SYS_CAST (func, rettype, parameters);
 215    is like  _GL_CXXALIAS_SYS (func, rettype, parameters);
 216    except that the C function func may have a slightly different declaration.
 217    A cast is used to silence the "invalid conversion" error that would
 218    otherwise occur.  */
 219 #if defined __cplusplus && defined GNULIB_NAMESPACE
 220 # define _GL_CXXALIAS_SYS_CAST(func,rettype,parameters) \
 221     namespace GNULIB_NAMESPACE                          \
 222     {                                                   \
 223       static const struct _gl_ ## func ## _wrapper      \
 224       {                                                 \
 225         typedef rettype (*type) parameters;             \
 226                                                         \
 227         inline operator type () const                   \
 228         {                                               \
 229           return reinterpret_cast<type>(::func);        \
 230         }                                               \
 231       } func = {};                                      \
 232     }                                                   \
 233     _GL_EXTERN_C int _gl_cxxalias_dummy
 234 #else
 235 # define _GL_CXXALIAS_SYS_CAST(func,rettype,parameters) \
 236     _GL_EXTERN_C int _gl_cxxalias_dummy
 237 #endif
 238
 239 /* _GL_CXXALIAS_SYS_CAST2 (func, rettype, parameters, rettype2, parameters2);
 240    is like  _GL_CXXALIAS_SYS (func, rettype, parameters);
 241    except that the C function is picked among a set of overloaded functions,
 242    namely the one with rettype2 and parameters2.  Two consecutive casts
 243    are used to silence the "cannot find a match" and "invalid conversion"
 244    errors that would otherwise occur.  */
 245 #if defined __cplusplus && defined GNULIB_NAMESPACE
 246   /* The outer cast must be a reinterpret_cast.
 247      The inner cast: When the function is defined as a set of overloaded
 248      functions, it works as a static_cast<>, choosing the designated variant.
 249      When the function is defined as a single variant, it works as a
 250      reinterpret_cast<>. The parenthesized cast syntax works both ways.  */
 251 # define _GL_CXXALIAS_SYS_CAST2(func,rettype,parameters,rettype2,parameters2) \
 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>((rettype2 (*) parameters2)(::func));  \
 261         }                                                                     \
 262       } func = {};                                                            \
 263     }                                                                         \
 264     _GL_EXTERN_C int _gl_cxxalias_dummy
 265 #else
 266 # define _GL_CXXALIAS_SYS_CAST2(func,rettype,parameters,rettype2,parameters2) \
 267     _GL_EXTERN_C int _gl_cxxalias_dummy
 268 #endif
 269
 270 /* _GL_CXXALIASWARN (func);
 271    causes a warning to be emitted when ::func is used but not when
 272    GNULIB_NAMESPACE::func is used.  func must be defined without overloaded
 273    variants.  */
 274 #if defined __cplusplus && defined GNULIB_NAMESPACE
 275 # define _GL_CXXALIASWARN(func) \
 276    _GL_CXXALIASWARN_1 (func, GNULIB_NAMESPACE)
 277 # define _GL_CXXALIASWARN_1(func,namespace) \
 278    _GL_CXXALIASWARN_2 (func, namespace)
 279 /* To work around GCC bug <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43881>,
 280    we enable the warning only when not optimizing.  */
 281 # if !(defined __GNUC__ && !defined __clang__ && __OPTIMIZE__)
 282 #  define _GL_CXXALIASWARN_2(func,namespace) \
 283     _GL_WARN_ON_USE (func, \
 284                      "The symbol ::" #func " refers to the system function. " \
 285                      "Use " #namespace "::" #func " instead.")
 286 # elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING
 287 #  define _GL_CXXALIASWARN_2(func,namespace) \
 288      extern __typeof__ (func) func
 289 # else
 290 #  define _GL_CXXALIASWARN_2(func,namespace) \
 291      _GL_EXTERN_C int _gl_cxxalias_dummy
 292 # endif
 293 #else
 294 # define _GL_CXXALIASWARN(func) \
 295     _GL_EXTERN_C int _gl_cxxalias_dummy
 296 #endif
 297
 298 /* _GL_CXXALIASWARN1 (func, rettype, parameters_and_attributes);
 299    causes a warning to be emitted when the given overloaded variant of ::func
 300    is used but not when GNULIB_NAMESPACE::func is used.  */
 301 #if defined __cplusplus && defined GNULIB_NAMESPACE
 302 # define _GL_CXXALIASWARN1(func,rettype,parameters_and_attributes) \
 303    _GL_CXXALIASWARN1_1 (func, rettype, parameters_and_attributes, \
 304                         GNULIB_NAMESPACE)
 305 # define _GL_CXXALIASWARN1_1(func,rettype,parameters_and_attributes,namespace) \
 306    _GL_CXXALIASWARN1_2 (func, rettype, parameters_and_attributes, namespace)
 307 /* To work around GCC bug <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43881>,
 308    we enable the warning only when not optimizing.  */
 309 # if !(defined __GNUC__ && !defined __clang__ && __OPTIMIZE__)
 310 #  define _GL_CXXALIASWARN1_2(func,rettype,parameters_and_attributes,namespace) \
 311     _GL_WARN_ON_USE_CXX (func, rettype, rettype, parameters_and_attributes, \
 312                          "The symbol ::" #func " refers to the system function. " \
 313                          "Use " #namespace "::" #func " instead.")
 314 # else
 315 #  define _GL_CXXALIASWARN1_2(func,rettype,parameters_and_attributes,namespace) \
 316      _GL_EXTERN_C int _gl_cxxalias_dummy
 317 # endif
 318 #else
 319 # define _GL_CXXALIASWARN1(func,rettype,parameters_and_attributes) \
 320     _GL_EXTERN_C int _gl_cxxalias_dummy
 321 #endif
 322
 323 #endif /* _GL_CXXDEFS_H */