lib/c++defs.h

   1 /* C++ compatible function declaration macros.
   2    Copyright (C) 2010-2018 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 General Public License as published
   6    by the Free Software Foundation; either version 3 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    General Public License for more details.
  13
  14    You should have received a copy of the GNU 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_RPL_CAST_1 (func, rpl_func, rettype, parameters);
 150    is like  _GL_CXXALIAS_RPL_1 (func, rpl_func, rettype, parameters);
 151    except that the C function rpl_func may have a slightly different
 152    declaration.  A cast is used to silence the "invalid conversion" error
 153    that would otherwise occur.  */
 154 #if defined __cplusplus && defined GNULIB_NAMESPACE
 155 # define _GL_CXXALIAS_RPL_CAST_1(func,rpl_func,rettype,parameters) \
 156     namespace GNULIB_NAMESPACE                                     \
 157     {                                                              \
 158       static const struct _gl_ ## func ## _wrapper                 \
 159       {                                                            \
 160         typedef rettype (*type) parameters;                        \
 161                                                                    \
 162         inline operator type () const                              \
 163         {                                                          \
 164           return reinterpret_cast<type>(::rpl_func);               \
 165         }                                                          \
 166       } func = {};                                                 \
 167     }                                                              \
 168     _GL_EXTERN_C int _gl_cxxalias_dummy
 169 #else
 170 # define _GL_CXXALIAS_RPL_CAST_1(func,rpl_func,rettype,parameters) \
 171     _GL_EXTERN_C int _gl_cxxalias_dummy
 172 #endif
 173
 174 /* _GL_CXXALIAS_SYS (func, rettype, parameters);
 175    declares a C++ alias called GNULIB_NAMESPACE::func
 176    that redirects to the system provided function func, if GNULIB_NAMESPACE
 177    is defined.
 178    Example:
 179      _GL_CXXALIAS_SYS (open, int, (const char *filename, int flags, ...));
 180
 181    Wrapping func in an object with an inline conversion operator
 182    avoids a reference to func unless GNULIB_NAMESPACE::func is
 183    actually used in the program.  */
 184 #if defined __cplusplus && defined GNULIB_NAMESPACE
 185 # define _GL_CXXALIAS_SYS(func,rettype,parameters)            \
 186     namespace GNULIB_NAMESPACE                                \
 187     {                                                         \
 188       static const struct _gl_ ## func ## _wrapper            \
 189       {                                                       \
 190         typedef rettype (*type) parameters;                   \
 191                                                               \
 192         inline operator type () const                         \
 193         {                                                     \
 194           return ::func;                                      \
 195         }                                                     \
 196       } func = {};                                            \
 197     }                                                         \
 198     _GL_EXTERN_C int _gl_cxxalias_dummy
 199 #else
 200 # define _GL_CXXALIAS_SYS(func,rettype,parameters) \
 201     _GL_EXTERN_C int _gl_cxxalias_dummy
 202 #endif
 203
 204 /* _GL_CXXALIAS_SYS_CAST (func, rettype, parameters);
 205    is like  _GL_CXXALIAS_SYS (func, rettype, parameters);
 206    except that the C function func may have a slightly different declaration.
 207    A cast is used to silence the "invalid conversion" error that would
 208    otherwise occur.  */
 209 #if defined __cplusplus && defined GNULIB_NAMESPACE
 210 # define _GL_CXXALIAS_SYS_CAST(func,rettype,parameters) \
 211     namespace GNULIB_NAMESPACE                          \
 212     {                                                   \
 213       static const struct _gl_ ## func ## _wrapper      \
 214       {                                                 \
 215         typedef rettype (*type) parameters;             \
 216                                                         \
 217         inline operator type () const                   \
 218         {                                               \
 219           return reinterpret_cast<type>(::func);        \
 220         }                                               \
 221       } func = {};                                      \
 222     }                                                   \
 223     _GL_EXTERN_C int _gl_cxxalias_dummy
 224 #else
 225 # define _GL_CXXALIAS_SYS_CAST(func,rettype,parameters) \
 226     _GL_EXTERN_C int _gl_cxxalias_dummy
 227 #endif
 228
 229 /* _GL_CXXALIAS_SYS_CAST2 (func, rettype, parameters, rettype2, parameters2);
 230    is like  _GL_CXXALIAS_SYS (func, rettype, parameters);
 231    except that the C function is picked among a set of overloaded functions,
 232    namely the one with rettype2 and parameters2.  Two consecutive casts
 233    are used to silence the "cannot find a match" and "invalid conversion"
 234    errors that would otherwise occur.  */
 235 #if defined __cplusplus && defined GNULIB_NAMESPACE
 236   /* The outer cast must be a reinterpret_cast.
 237      The inner cast: When the function is defined as a set of overloaded
 238      functions, it works as a static_cast<>, choosing the designated variant.
 239      When the function is defined as a single variant, it works as a
 240      reinterpret_cast<>. The parenthesized cast syntax works both ways.  */
 241 # define _GL_CXXALIAS_SYS_CAST2(func,rettype,parameters,rettype2,parameters2) \
 242     namespace GNULIB_NAMESPACE                                                \
 243     {                                                                         \
 244       static const struct _gl_ ## func ## _wrapper                            \
 245       {                                                                       \
 246         typedef rettype (*type) parameters;                                   \
 247                                                                               \
 248         inline operator type () const                                         \
 249         {                                                                     \
 250           return reinterpret_cast<type>((rettype2 (*) parameters2)(::func));  \
 251         }                                                                     \
 252       } func = {};                                                            \
 253     }                                                                         \
 254     _GL_EXTERN_C int _gl_cxxalias_dummy
 255 #else
 256 # define _GL_CXXALIAS_SYS_CAST2(func,rettype,parameters,rettype2,parameters2) \
 257     _GL_EXTERN_C int _gl_cxxalias_dummy
 258 #endif
 259
 260 /* _GL_CXXALIASWARN (func);
 261    causes a warning to be emitted when ::func is used but not when
 262    GNULIB_NAMESPACE::func is used.  func must be defined without overloaded
 263    variants.  */
 264 #if defined __cplusplus && defined GNULIB_NAMESPACE
 265 # define _GL_CXXALIASWARN(func) \
 266    _GL_CXXALIASWARN_1 (func, GNULIB_NAMESPACE)
 267 # define _GL_CXXALIASWARN_1(func,namespace) \
 268    _GL_CXXALIASWARN_2 (func, namespace)
 269 /* To work around GCC bug <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43881>,
 270    we enable the warning only when not optimizing.  */
 271 # if !__OPTIMIZE__
 272 #  define _GL_CXXALIASWARN_2(func,namespace) \
 273     _GL_WARN_ON_USE (func, \
 274                      "The symbol ::" #func " refers to the system function. " \
 275                      "Use " #namespace "::" #func " instead.")
 276 # elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING
 277 #  define _GL_CXXALIASWARN_2(func,namespace) \
 278      extern __typeof__ (func) func
 279 # else
 280 #  define _GL_CXXALIASWARN_2(func,namespace) \
 281      _GL_EXTERN_C int _gl_cxxalias_dummy
 282 # endif
 283 #else
 284 # define _GL_CXXALIASWARN(func) \
 285     _GL_EXTERN_C int _gl_cxxalias_dummy
 286 #endif
 287
 288 /* _GL_CXXALIASWARN1 (func, rettype, parameters_and_attributes);
 289    causes a warning to be emitted when the given overloaded variant of ::func
 290    is used but not when GNULIB_NAMESPACE::func is used.  */
 291 #if defined __cplusplus && defined GNULIB_NAMESPACE
 292 # define _GL_CXXALIASWARN1(func,rettype,parameters_and_attributes) \
 293    _GL_CXXALIASWARN1_1 (func, rettype, parameters_and_attributes, \
 294                         GNULIB_NAMESPACE)
 295 # define _GL_CXXALIASWARN1_1(func,rettype,parameters_and_attributes,namespace) \
 296    _GL_CXXALIASWARN1_2 (func, rettype, parameters_and_attributes, namespace)
 297 /* To work around GCC bug <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43881>,
 298    we enable the warning only when not optimizing.  */
 299 # if !__OPTIMIZE__
 300 #  define _GL_CXXALIASWARN1_2(func,rettype,parameters_and_attributes,namespace) \
 301     _GL_WARN_ON_USE_CXX (func, rettype, parameters_and_attributes, \
 302                          "The symbol ::" #func " refers to the system function. " \
 303                          "Use " #namespace "::" #func " instead.")
 304 # elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING
 305 #  define _GL_CXXALIASWARN1_2(func,rettype,parameters_and_attributes,namespace) \
 306      extern __typeof__ (func) func
 307 # else
 308 #  define _GL_CXXALIASWARN1_2(func,rettype,parameters_and_attributes,namespace) \
 309      _GL_EXTERN_C int _gl_cxxalias_dummy
 310 # endif
 311 #else
 312 # define _GL_CXXALIASWARN1(func,rettype,parameters_and_attributes) \
 313     _GL_EXTERN_C int _gl_cxxalias_dummy
 314 #endif
 315
 316 #endif /* _GL_CXXDEFS_H */