glib/gmessages.h

   1 /* GLIB - Library of useful routines for C programming
   2  * Copyright (C) 1995-1997  Peter Mattis, Spencer Kimball and Josh MacDonald
   3  *
   4  * This library is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU Lesser General Public
   6  * License as published by the Free Software Foundation; either
   7  * version 2.1 of the License, or (at your option) any later version.
   8  *
   9  * This library 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
  15  * License along with this library; if not, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 /*
  19  * Modified by the GLib Team and others 1997-2000.  See the AUTHORS
  20  * file for a list of people on the GLib Team.  See the ChangeLog
  21  * files for a list of changes.  These files are distributed with
  22  * GLib at ftp://ftp.gtk.org/pub/gtk/.
  23  */
  24
  25 #ifndef __G_MESSAGES_H__
  26 #define __G_MESSAGES_H__
  27
  28 #if !defined (__GLIB_H_INSIDE__) && !defined (GLIB_COMPILATION)
  29 #error "Only <glib.h> can be included directly."
  30 #endif
  31
  32 #include <stdarg.h>
  33 #include <glib/gtypes.h>
  34 #include <glib/gmacros.h>
  35 #include <glib/gvariant.h>
  36
  37 G_BEGIN_DECLS
  38
  39 /* calculate a string size, guaranteed to fit format + args.
  40  */
  41 GLIB_AVAILABLE_IN_ALL
  42 gsize   g_printf_string_upper_bound (const gchar* format,
  43                                      va_list      args) G_GNUC_PRINTF(1, 0);
  44
  45 /* Log level shift offset for user defined
  46  * log levels (0-7 are used by GLib).
  47  */
  48 #define G_LOG_LEVEL_USER_SHIFT  (8)
  49
  50 /* Glib log levels and flags.
  51  */
  52 typedef enum
  53 {
  54   /* log flags */
  55   G_LOG_FLAG_RECURSION          = 1 << 0,
  56   G_LOG_FLAG_FATAL              = 1 << 1,
  57
  58   /* GLib log levels */
  59   G_LOG_LEVEL_ERROR             = 1 << 2,       /* always fatal */
  60   G_LOG_LEVEL_CRITICAL          = 1 << 3,
  61   G_LOG_LEVEL_WARNING           = 1 << 4,
  62   G_LOG_LEVEL_MESSAGE           = 1 << 5,
  63   G_LOG_LEVEL_INFO              = 1 << 6,
  64   G_LOG_LEVEL_DEBUG             = 1 << 7,
  65
  66   G_LOG_LEVEL_MASK              = ~(G_LOG_FLAG_RECURSION | G_LOG_FLAG_FATAL)
  67 } GLogLevelFlags;
  68
  69 /* GLib log levels that are considered fatal by default */
  70 #define G_LOG_FATAL_MASK        (G_LOG_FLAG_RECURSION | G_LOG_LEVEL_ERROR)
  71
  72 typedef void            (*GLogFunc)             (const gchar   *log_domain,
  73                                                  GLogLevelFlags log_level,
  74                                                  const gchar   *message,
  75                                                  gpointer       user_data);
  76
  77 /* Logging mechanism
  78  */
  79 GLIB_AVAILABLE_IN_ALL
  80 guint           g_log_set_handler       (const gchar    *log_domain,
  81                                          GLogLevelFlags  log_levels,
  82                                          GLogFunc        log_func,
  83                                          gpointer        user_data);
  84 GLIB_AVAILABLE_IN_2_46
  85 guint           g_log_set_handler_full  (const gchar    *log_domain,
  86                                          GLogLevelFlags  log_levels,
  87                                          GLogFunc        log_func,
  88                                          gpointer        user_data,
  89                                          GDestroyNotify  destroy);
  90 GLIB_AVAILABLE_IN_ALL
  91 void            g_log_remove_handler    (const gchar    *log_domain,
  92                                          guint           handler_id);
  93 GLIB_AVAILABLE_IN_ALL
  94 void            g_log_default_handler   (const gchar    *log_domain,
  95                                          GLogLevelFlags  log_level,
  96                                          const gchar    *message,
  97                                          gpointer        unused_data);
  98 GLIB_AVAILABLE_IN_ALL
  99 GLogFunc        g_log_set_default_handler (GLogFunc      log_func,
 100                                            gpointer      user_data);
 101 GLIB_AVAILABLE_IN_ALL
 102 void            g_log                   (const gchar    *log_domain,
 103                                          GLogLevelFlags  log_level,
 104                                          const gchar    *format,
 105                                          ...) G_GNUC_PRINTF (3, 4);
 106 GLIB_AVAILABLE_IN_ALL
 107 void            g_logv                  (const gchar    *log_domain,
 108                                          GLogLevelFlags  log_level,
 109                                          const gchar    *format,
 110                                          va_list         args) G_GNUC_PRINTF(3, 0);
 111 GLIB_AVAILABLE_IN_ALL
 112 GLogLevelFlags  g_log_set_fatal_mask    (const gchar    *log_domain,
 113                                          GLogLevelFlags  fatal_mask);
 114 GLIB_AVAILABLE_IN_ALL
 115 GLogLevelFlags  g_log_set_always_fatal  (GLogLevelFlags  fatal_mask);
 116
 117 /* Structured logging mechanism. */
 118
 119 /**
 120  * GLogWriterOutput:
 121  * @G_LOG_WRITER_HANDLED: Log writer has handled the log entry.
 122  * @G_LOG_WRITER_UNHANDLED: Log writer could not handle the log entry.
 123  *
 124  * Return values from #GLogWriterFuncs to indicate whether the given log entry
 125  * was successfully handled by the writer, or whether there was an error in
 126  * handling it (and hence a fallback writer should be used).
 127  *
 128  * If a #GLogWriterFunc ignores a log entry, it should return
 129  * %G_LOG_WRITER_HANDLED.
 130  *
 131  * Since: 2.50
 132  */
 133 typedef enum
 134 {
 135   G_LOG_WRITER_HANDLED = 1,
 136   G_LOG_WRITER_UNHANDLED = 0,
 137 } GLogWriterOutput;
 138
 139 /**
 140  * GLogField:
 141  * @key: field name (UTF-8 string)
 142  * @value: field value (arbitrary bytes)
 143  * @length: length of @value, in bytes, or -1 if it is nul-terminated
 144  *
 145  * Structure representing a single field in a structured log entry. See
 146  * g_log_structured() for details.
 147  *
 148  * Log fields may contain arbitrary values, including binary with embedded nul
 149  * bytes. If the field contains a string, the string must be UTF-8 encoded and
 150  * have a trailing nul byte. Otherwise, @length must be set to a non-negative
 151  * value.
 152  *
 153  * Since: 2.50
 154  */
 155 typedef struct _GLogField GLogField;
 156 struct _GLogField
 157 {
 158   const gchar *key;
 159   gconstpointer value;
 160   gssize length;
 161 };
 162
 163 /**
 164  * GLogWriterFunc:
 165  * @log_level: log level of the message
 166  * @fields: (array length=n_fields): fields forming the message
 167  * @n_fields: number of @fields
 168  * @user_data: user data passed to g_log_set_writer_func()
 169  *
 170  * Writer function for log entries. A log entry is a collection of one or more
 171  * #GLogFields, using the standard [field names from journal
 172  * specification](https://www.freedesktop.org/software/systemd/man/systemd.journal-fields.html).
 173  * See g_log_structured() for more information.
 174  *
 175  * Writer functions must ignore fields which they do not recognise, unless they
 176  * can write arbitrary binary output, as field values may be arbitrary binary.
 177  *
 178  * @log_level is guaranteed to be included in @fields as the `PRIORITY` field,
 179  * but is provided separately for convenience of deciding whether or where to
 180  * output the log entry.
 181  *
 182  * Writer functions should return %G_LOG_WRITER_HANDLED if they handled the log
 183  * message successfully or if they deliberately ignored it. If there was an
 184  * error handling the message (for example, if the writer function is meant to
 185  * send messages to a remote logging server and there is a network error), it
 186  * should return %G_LOG_WRITER_UNHANDLED. This allows writer functions to be
 187  * chained and fall back to simpler handlers in case of failure.
 188  *
 189  * Returns: %G_LOG_WRITER_HANDLED if the log entry was handled successfully;
 190  *    %G_LOG_WRITER_UNHANDLED otherwise
 191  * Since: 2.50
 192  */
 193 typedef GLogWriterOutput (*GLogWriterFunc)     (GLogLevelFlags   log_level,
 194                                                 const GLogField *fields,
 195                                                 gsize            n_fields,
 196                                                 gpointer         user_data);
 197
 198 GLIB_AVAILABLE_IN_2_50
 199 void             g_log_structured              (const gchar     *log_domain,
 200                                                 GLogLevelFlags   log_level,
 201                                                 ...);
 202 GLIB_AVAILABLE_IN_2_50
 203 void             g_log_structured_array        (GLogLevelFlags   log_level,
 204                                                 const GLogField *fields,
 205                                                 gsize            n_fields);
 206
 207 GLIB_AVAILABLE_IN_2_50
 208 void             g_log_variant                 (const gchar     *log_domain,
 209                                                 GLogLevelFlags   log_level,
 210                                                 GVariant        *fields);
 211
 212 GLIB_AVAILABLE_IN_2_50
 213 void             g_log_set_writer_func         (GLogWriterFunc   func,
 214                                                 gpointer         user_data,
 215                                                 GDestroyNotify   user_data_free);
 216
 217 GLIB_AVAILABLE_IN_2_50
 218 gboolean         g_log_writer_supports_color   (gint             output_fd);
 219 GLIB_AVAILABLE_IN_2_50
 220 gboolean         g_log_writer_is_journald      (gint             output_fd);
 221
 222 GLIB_AVAILABLE_IN_2_50
 223 gchar           *g_log_writer_format_fields    (GLogLevelFlags   log_level,
 224                                                 const GLogField *fields,
 225                                                 gsize            n_fields,
 226                                                 gboolean         use_color);
 227
 228 GLIB_AVAILABLE_IN_2_50
 229 GLogWriterOutput g_log_writer_journald         (GLogLevelFlags   log_level,
 230                                                 const GLogField *fields,
 231                                                 gsize            n_fields,
 232                                                 gpointer         user_data);
 233 GLIB_AVAILABLE_IN_2_50
 234 GLogWriterOutput g_log_writer_standard_streams (GLogLevelFlags   log_level,
 235                                                 const GLogField *fields,
 236                                                 gsize            n_fields,
 237                                                 gpointer         user_data);
 238 GLIB_AVAILABLE_IN_2_50
 239 GLogWriterOutput g_log_writer_default          (GLogLevelFlags   log_level,
 240                                                 const GLogField *fields,
 241                                                 gsize            n_fields,
 242                                                 gpointer         user_data);
 243
 244 /**
 245  * G_DEBUG_HERE:
 246  *
 247  * A convenience form of g_log_structured(), recommended to be added to
 248  * functions when debugging. It prints the current monotonic time and the code
 249  * location using %G_STRLOC.
 250  *
 251  * Since: 2.50
 252  */
 253 #define G_DEBUG_HERE()                                          \
 254   g_log_structured (G_LOG_DOMAIN, G_LOG_LEVEL_DEBUG,            \
 255                     "CODE_FILE", __FILE__,                      \
 256                     "CODE_LINE", G_STRINGIFY (__LINE__),        \
 257                     "CODE_FUNC", G_STRFUNC,                      \
 258                     "MESSAGE", "%" G_GINT64_FORMAT ": %s",      \
 259                     g_get_monotonic_time (), G_STRLOC)
 260
 261 /* internal */
 262 void    _g_log_fallback_handler (const gchar   *log_domain,
 263                                                  GLogLevelFlags log_level,
 264                                                  const gchar   *message,
 265                                                  gpointer       unused_data);
 266
 267 /* Internal functions, used to implement the following macros */
 268 GLIB_AVAILABLE_IN_ALL
 269 void g_return_if_fail_warning (const char *log_domain,
 270                                const char *pretty_function,
 271                                const char *expression) G_ANALYZER_NORETURN;
 272 GLIB_AVAILABLE_IN_ALL
 273 void g_warn_message           (const char     *domain,
 274                                const char     *file,
 275                                int             line,
 276                                const char     *func,
 277                                const char     *warnexpr) G_ANALYZER_NORETURN;
 278 GLIB_DEPRECATED
 279 void g_assert_warning         (const char *log_domain,
 280                                const char *file,
 281                                const int   line,
 282                                const char *pretty_function,
 283                                const char *expression) G_GNUC_NORETURN;
 284
 285
 286 #ifndef G_LOG_DOMAIN
 287 #define G_LOG_DOMAIN    ((gchar*) 0)
 288 #endif  /* G_LOG_DOMAIN */
 289
 290 #if defined(G_HAVE_ISO_VARARGS) && !G_ANALYZER_ANALYZING
 291 #ifdef G_LOG_USE_STRUCTURED
 292 #define g_error(...)  G_STMT_START {                                            \
 293                         g_log_structured (G_LOG_DOMAIN, G_LOG_LEVEL_ERROR,      \
 294                                           "CODE_FILE", __FILE__,                \
 295                                           "CODE_LINE", G_STRINGIFY (__LINE__),  \
 296                                           "CODE_FUNC", G_STRFUNC,                \
 297                                           "MESSAGE", __VA_ARGS__);              \
 298                         for (;;) ;                                              \
 299                       } G_STMT_END
 300 #define g_message(...)  g_log_structured (G_LOG_DOMAIN, G_LOG_LEVEL_MESSAGE,    \
 301                                           "CODE_FILE", __FILE__,                \
 302                                           "CODE_LINE", G_STRINGIFY (__LINE__),  \
 303                                           "CODE_FUNC", G_STRFUNC,                \
 304                                           "MESSAGE", __VA_ARGS__)
 305 #define g_critical(...) g_log_structured (G_LOG_DOMAIN, G_LOG_LEVEL_CRITICAL,   \
 306                                           "CODE_FILE", __FILE__,                \
 307                                           "CODE_LINE", G_STRINGIFY (__LINE__),  \
 308                                           "CODE_FUNC", G_STRFUNC,                \
 309                                           "MESSAGE", __VA_ARGS__)
 310 #define g_warning(...)  g_log_structured (G_LOG_DOMAIN, G_LOG_LEVEL_WARNING,    \
 311                                           "CODE_FILE", __FILE__,                \
 312                                           "CODE_LINE", G_STRINGIFY (__LINE__),  \
 313                                           "CODE_FUNC", G_STRFUNC,                \
 314                                           "MESSAGE", __VA_ARGS__)
 315 #define g_info(...)     g_log_structured (G_LOG_DOMAIN, G_LOG_LEVEL_INFO,       \
 316                                           "CODE_FILE", __FILE__,                \
 317                                           "CODE_LINE", G_STRINGIFY (__LINE__),  \
 318                                           "CODE_FUNC", G_STRFUNC,                \
 319                                           "MESSAGE", __VA_ARGS__)
 320 #define g_debug(...)    g_log_structured (G_LOG_DOMAIN, G_LOG_LEVEL_DEBUG,      \
 321                                           "CODE_FILE", __FILE__,                \
 322                                           "CODE_LINE", G_STRINGIFY (__LINE__),  \
 323                                           "CODE_FUNC", G_STRFUNC,                \
 324                                           "MESSAGE", __VA_ARGS__)
 325 #else
 326 /* for(;;) ; so that GCC knows that control doesn't go past g_error().
 327  * Put space before ending semicolon to avoid C++ build warnings.
 328  */
 329 #define g_error(...)  G_STMT_START {                 \
 330                         g_log (G_LOG_DOMAIN,         \
 331                                G_LOG_LEVEL_ERROR,    \
 332                                __VA_ARGS__);         \
 333                         for (;;) ;                   \
 334                       } G_STMT_END
 335 #define g_message(...)  g_log (G_LOG_DOMAIN,         \
 336                                G_LOG_LEVEL_MESSAGE,  \
 337                                __VA_ARGS__)
 338 #define g_critical(...) g_log (G_LOG_DOMAIN,         \
 339                                G_LOG_LEVEL_CRITICAL, \
 340                                __VA_ARGS__)
 341 #define g_warning(...)  g_log (G_LOG_DOMAIN,         \
 342                                G_LOG_LEVEL_WARNING,  \
 343                                __VA_ARGS__)
 344 #define g_info(...)     g_log (G_LOG_DOMAIN,         \
 345                                G_LOG_LEVEL_INFO,     \
 346                                __VA_ARGS__)
 347 #define g_debug(...)    g_log (G_LOG_DOMAIN,         \
 348                                G_LOG_LEVEL_DEBUG,    \
 349                                __VA_ARGS__)
 350 #endif
 351 #elif defined(G_HAVE_GNUC_VARARGS)  && !G_ANALYZER_ANALYZING
 352 #ifdef G_LOG_USE_STRUCTURED
 353 #define g_error(format...)   G_STMT_START {                                          \
 354                                g_log_structured (G_LOG_DOMAIN, G_LOG_LEVEL_ERROR,    \
 355                                                 "CODE_FILE", __FILE__,               \
 356                                                 "CODE_LINE", G_STRINGIFY (__LINE__), \
 357                                                 "CODE_FUNC", G_STRFUNC,               \
 358                                                 "MESSAGE", format);                  \
 359                                for (;;) ;                                            \
 360                              } G_STMT_END
 361 #define g_message(format...)  g_log_structured (G_LOG_DOMAIN, G_LOG_LEVEL_MESSAGE,   \
 362                                                "CODE_FILE", __FILE__,                \
 363                                                "CODE_LINE", G_STRINGIFY (__LINE__),  \
 364                                                "CODE_FUNC", G_STRFUNC,                \
 365                                                "MESSAGE", format)
 366 #define g_critical(format...) g_log_structured (G_LOG_DOMAIN, G_LOG_LEVEL_CRITICAL,  \
 367                                                 "CODE_FILE", __FILE__,               \
 368                                                 "CODE_LINE", G_STRINGIFY (__LINE__), \
 369                                                 "CODE_FUNC", G_STRFUNC,               \
 370                                                 "MESSAGE", format)
 371 #define g_warning(format...)  g_log_structured (G_LOG_DOMAIN, G_LOG_LEVEL_WARNING,   \
 372                                                 "CODE_FILE", __FILE__,               \
 373                                                 "CODE_LINE", G_STRINGIFY (__LINE__), \
 374                                                 "CODE_FUNC", G_STRFUNC,               \
 375                                                 "MESSAGE", format)
 376 #define g_info(format...)     g_log_structured (G_LOG_DOMAIN, G_LOG_LEVEL_INFO,      \
 377                                                 "CODE_FILE", __FILE__,               \
 378                                                 "CODE_LINE", G_STRINGIFY (__LINE__), \
 379                                                 "CODE_FUNC", G_STRFUNC,               \
 380                                                 "MESSAGE", format)
 381 #define g_debug(format...)    g_log_structured (G_LOG_DOMAIN, G_LOG_LEVEL_DEBUG,     \
 382                                                 "CODE_FILE", __FILE__,               \
 383                                                 "CODE_LINE", G_STRINGIFY (__LINE__), \
 384                                                 "CODE_FUNC", G_STRFUNC,               \
 385                                                 "MESSAGE", format)
 386 #else
 387 #define g_error(format...)    G_STMT_START {                 \
 388                                 g_log (G_LOG_DOMAIN,         \
 389                                        G_LOG_LEVEL_ERROR,    \
 390                                        format);              \
 391                                 for (;;) ;                   \
 392                               } G_STMT_END
 393
 394 #define g_message(format...)    g_log (G_LOG_DOMAIN,         \
 395                                        G_LOG_LEVEL_MESSAGE,  \
 396                                        format)
 397 #define g_critical(format...)   g_log (G_LOG_DOMAIN,         \
 398                                        G_LOG_LEVEL_CRITICAL, \
 399                                        format)
 400 #define g_warning(format...)    g_log (G_LOG_DOMAIN,         \
 401                                        G_LOG_LEVEL_WARNING,  \
 402                                        format)
 403 #define g_info(format...)       g_log (G_LOG_DOMAIN,         \
 404                                        G_LOG_LEVEL_INFO,     \
 405                                        format)
 406 #define g_debug(format...)      g_log (G_LOG_DOMAIN,         \
 407                                        G_LOG_LEVEL_DEBUG,    \
 408                                        format)
 409 #endif
 410 #else   /* no varargs macros */
 411 static void g_error (const gchar *format, ...) G_GNUC_NORETURN G_ANALYZER_NORETURN;
 412 static void g_critical (const gchar *format, ...) G_ANALYZER_NORETURN;
 413
 414 static inline void
 415 g_error (const gchar *format,
 416          ...)
 417 {
 418   va_list args;
 419   va_start (args, format);
 420   g_logv (G_LOG_DOMAIN, G_LOG_LEVEL_ERROR, format, args);
 421   va_end (args);
 422
 423   for(;;) ;
 424 }
 425 static inline void
 426 g_message (const gchar *format,
 427            ...)
 428 {
 429   va_list args;
 430   va_start (args, format);
 431   g_logv (G_LOG_DOMAIN, G_LOG_LEVEL_MESSAGE, format, args);
 432   va_end (args);
 433 }
 434 static inline void
 435 g_critical (const gchar *format,
 436             ...)
 437 {
 438   va_list args;
 439   va_start (args, format);
 440   g_logv (G_LOG_DOMAIN, G_LOG_LEVEL_CRITICAL, format, args);
 441   va_end (args);
 442 }
 443 static inline void
 444 g_warning (const gchar *format,
 445            ...)
 446 {
 447   va_list args;
 448   va_start (args, format);
 449   g_logv (G_LOG_DOMAIN, G_LOG_LEVEL_WARNING, format, args);
 450   va_end (args);
 451 }
 452 static inline void
 453 g_info (const gchar *format,
 454         ...)
 455 {
 456   va_list args;
 457   va_start (args, format);
 458   g_logv (G_LOG_DOMAIN, G_LOG_LEVEL_INFO, format, args);
 459   va_end (args);
 460 }
 461 static inline void
 462 g_debug (const gchar *format,
 463          ...)
 464 {
 465   va_list args;
 466   va_start (args, format);
 467   g_logv (G_LOG_DOMAIN, G_LOG_LEVEL_DEBUG, format, args);
 468   va_end (args);
 469 }
 470 #endif  /* !__GNUC__ */
 471
 472 /**
 473  * GPrintFunc:
 474  * @string: the message to output
 475  *
 476  * Specifies the type of the print handler functions.
 477  * These are called with the complete formatted string to output.
 478  */
 479 typedef void    (*GPrintFunc)           (const gchar    *string);
 480 GLIB_AVAILABLE_IN_ALL
 481 void            g_print                 (const gchar    *format,
 482                                          ...) G_GNUC_PRINTF (1, 2);
 483 GLIB_AVAILABLE_IN_ALL
 484 GPrintFunc      g_set_print_handler     (GPrintFunc      func);
 485 GLIB_AVAILABLE_IN_ALL
 486 void            g_printerr              (const gchar    *format,
 487                                          ...) G_GNUC_PRINTF (1, 2);
 488 GLIB_AVAILABLE_IN_ALL
 489 GPrintFunc      g_set_printerr_handler  (GPrintFunc      func);
 490
 491 /**
 492  * g_warn_if_reached:
 493  *
 494  * Logs a warning.
 495  *
 496  * Since: 2.16
 497  */
 498 #define g_warn_if_reached() \
 499   do { \
 500     g_warn_message (G_LOG_DOMAIN, __FILE__, __LINE__, G_STRFUNC, NULL); \
 501   } while (0)
 502
 503 /**
 504  * g_warn_if_fail:
 505  * @expr: the expression to check
 506  *
 507  * Logs a warning if the expression is not true.
 508  *
 509  * Since: 2.16
 510  */
 511 #define g_warn_if_fail(expr) \
 512   do { \
 513     if G_LIKELY (expr) ; \
 514     else g_warn_message (G_LOG_DOMAIN, __FILE__, __LINE__, G_STRFUNC, #expr); \
 515   } while (0)
 516
 517 #ifdef G_DISABLE_CHECKS
 518
 519 /**
 520  * g_return_if_fail:
 521  * @expr: the expression to check
 522  *
 523  * Verifies that the expression @expr, usually representing a precondition,
 524  * evaluates to %TRUE. If the function returns a value, use
 525  * g_return_val_if_fail() instead.
 526  *
 527  * If @expr evaluates to %FALSE, the current function should be considered to
 528  * have undefined behaviour (a programmer error). The only correct solution
 529  * to such an error is to change the module that is calling the current
 530  * function, so that it avoids this incorrect call.
 531  *
 532  * To make this undefined behaviour visible, if @expr evaluates to %FALSE,
 533  * the result is usually that a critical message is logged and the current
 534  * function returns.
 535  *
 536  * If `G_DISABLE_CHECKS` is defined then the check is not performed.  You
 537  * should therefore not depend on any side effects of @expr.
 538  *
 539  * To debug failure of a g_return_if_fail() check, run the code under a debugger
 540  * with `G_DEBUG=fatal-criticals` or `G_DEBUG=fatal-warnings` defined in the
 541  * environment (see [Running GLib Applications](glib-running.html)):
 542  *
 543  * |[
 544  *   G_DEBUG=fatal-warnings gdb ./my-program
 545  * ]|
 546  *
 547  * Any unrelated failures can be skipped over in
 548  * [gdb](https://www.gnu.org/software/gdb/) using the `continue` command.
 549  */
 550 #define g_return_if_fail(expr) G_STMT_START{ (void)0; }G_STMT_END
 551
 552 /**
 553  * g_return_val_if_fail:
 554  * @expr: the expression to check
 555  * @val: the value to return from the current function
 556  *       if the expression is not true
 557  *
 558  * Verifies that the expression @expr, usually representing a precondition,
 559  * evaluates to %TRUE. If the function does not return a value, use
 560  * g_return_if_fail() instead.
 561  *
 562  * If @expr evaluates to %FALSE, the current function should be considered to
 563  * have undefined behaviour (a programmer error). The only correct solution
 564  * to such an error is to change the module that is calling the current
 565  * function, so that it avoids this incorrect call.
 566  *
 567  * To make this undefined behaviour visible, if @expr evaluates to %FALSE,
 568  * the result is usually that a critical message is logged and @val is
 569  * returned from the current function.
 570  *
 571  * If `G_DISABLE_CHECKS` is defined then the check is not performed.  You
 572  * should therefore not depend on any side effects of @expr.
 573  *
 574  * See g_return_if_fail() for guidance on how to debug failure of this check.
 575  */
 576 #define g_return_val_if_fail(expr,val) G_STMT_START{ (void)0; }G_STMT_END
 577
 578 /**
 579  * g_return_if_reached:
 580  *
 581  * Logs a critical message and returns from the current function.
 582  * This can only be used in functions which do not return a value.
 583  *
 584  * See g_return_if_fail() for guidance on how to debug failure of this check.
 585  */
 586 #define g_return_if_reached() G_STMT_START{ return; }G_STMT_END
 587
 588 /**
 589  * g_return_val_if_reached:
 590  * @val: the value to return from the current function
 591  *
 592  * Logs a critical message and returns @val.
 593  *
 594  * See g_return_if_fail() for guidance on how to debug failure of this check.
 595  */
 596 #define g_return_val_if_reached(val) G_STMT_START{ return (val); }G_STMT_END
 597
 598 #else /* !G_DISABLE_CHECKS */
 599
 600 #define g_return_if_fail(expr)          G_STMT_START{                   \
 601      if G_LIKELY(expr) { } else                                         \
 602        {                                                                \
 603          g_return_if_fail_warning (G_LOG_DOMAIN,                        \
 604                                    G_STRFUNC,                           \
 605                                    #expr);                              \
 606          return;                                                        \
 607        };                               }G_STMT_END
 608
 609 #define g_return_val_if_fail(expr,val)  G_STMT_START{                   \
 610      if G_LIKELY(expr) { } else                                         \
 611        {                                                                \
 612          g_return_if_fail_warning (G_LOG_DOMAIN,                        \
 613                                    G_STRFUNC,                           \
 614                                    #expr);                              \
 615          return (val);                                                  \
 616        };                               }G_STMT_END
 617
 618 #define g_return_if_reached()           G_STMT_START{                   \
 619      g_log (G_LOG_DOMAIN,                                               \
 620             G_LOG_LEVEL_CRITICAL,                                       \
 621             "file %s: line %d (%s): should not be reached",             \
 622             __FILE__,                                                   \
 623             __LINE__,                                                   \
 624             G_STRFUNC);                                                 \
 625      return;                            }G_STMT_END
 626
 627 #define g_return_val_if_reached(val)    G_STMT_START{                   \
 628      g_log (G_LOG_DOMAIN,                                               \
 629             G_LOG_LEVEL_CRITICAL,                                       \
 630             "file %s: line %d (%s): should not be reached",             \
 631             __FILE__,                                                   \
 632             __LINE__,                                                   \
 633             G_STRFUNC);                                                 \
 634      return (val);                      }G_STMT_END
 635
 636 #endif /* !G_DISABLE_CHECKS */
 637
 638 G_END_DECLS
 639
 640 #endif /* __G_MESSAGES_H__ */