glib/gerror.c

   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 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, write to the
  16  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17  * Boston, MA 02111-1307, USA.
  18  */
  19
  20 /*
  21  * Modified by the GLib Team and others 1997-2000.  See the AUTHORS
  22  * file for a list of people on the GLib Team.  See the ChangeLog
  23  * files for a list of changes.  These files are distributed with
  24  * GLib at ftp://ftp.gtk.org/pub/gtk/.
  25  */
  26
  27 /**
  28  * SECTION:error_reporting
  29  * @Title: Error Reporting
  30  * @Short_description: a system for reporting errors
  31  *
  32  * GLib provides a standard method of reporting errors from a called
  33  * function to the calling code. (This is the same problem solved by
  34  * exceptions in other languages.) It's important to understand that
  35  * this method is both a <emphasis>data type</emphasis> (the #GError
  36  * object) and a <emphasis>set of rules.</emphasis> If you use #GError
  37  * incorrectly, then your code will not properly interoperate with other
  38  * code that uses #GError, and users of your API will probably get confused.
  39  *
  40  * First and foremost: <emphasis>#GError should only be used to report
  41  * recoverable runtime errors, never to report programming
  42  * errors.</emphasis> If the programmer has screwed up, then you should
  43  * use g_warning(), g_return_if_fail(), g_assert(), g_error(), or some
  44  * similar facility. (Incidentally, remember that the g_error() function
  45  * should <emphasis>only</emphasis> be used for programming errors, it
  46  * should not be used to print any error reportable via #GError.)
  47  *
  48  * Examples of recoverable runtime errors are "file not found" or
  49  * "failed to parse input." Examples of programming errors are "NULL
  50  * passed to strcmp()" or "attempted to free the same pointer twice."
  51  * These two kinds of errors are fundamentally different: runtime errors
  52  * should be handled or reported to the user, programming errors should
  53  * be eliminated by fixing the bug in the program. This is why most
  54  * functions in GLib and GTK+ do not use the #GError facility.
  55  *
  56  * Functions that can fail take a return location for a #GError as their
  57  * last argument. For example:
  58  * |[
  59  * gboolean g_file_get_contents (const gchar  *filename,
  60  *                               gchar       **contents,
  61  *                               gsize        *length,
  62  *                               GError      **error);
  63  * ]|
  64  * If you pass a non-%NULL value for the <literal>error</literal>
  65  * argument, it should point to a location where an error can be placed.
  66  * For example:
  67  * |[
  68  * gchar *contents;
  69  * GError *err = NULL;
  70  * g_file_get_contents ("foo.txt", &amp;contents, NULL, &amp;err);
  71  * g_assert ((contents == NULL &amp;&amp; err != NULL) || (contents != NULL &amp;&amp; err == NULL));
  72  * if (err != NULL)
  73  *   {
  74  *     /&ast; Report error to user, and free error &ast;/
  75  *     g_assert (contents == NULL);
  76  *     fprintf (stderr, "Unable to read file: &percnt;s\n", err->message);
  77  *     g_error_free (err);
  78  *   }
  79  * else
  80  *   {
  81  *     /&ast; Use file contents &ast;/
  82  *     g_assert (contents != NULL);
  83  *   }
  84  * ]|
  85  * Note that <literal>err != NULL</literal> in this example is a
  86  * <emphasis>reliable</emphasis> indicator of whether
  87  * g_file_get_contents() failed. Additionally, g_file_get_contents()
  88  * returns a boolean which indicates whether it was successful.
  89  *
  90  * Because g_file_get_contents() returns %FALSE on failure, if you
  91  * are only interested in whether it failed and don't need to display
  92  * an error message, you can pass %NULL for the <literal>error</literal>
  93  * argument:
  94  * |[
  95  * if (g_file_get_contents ("foo.txt", &amp;contents, NULL, NULL)) /&ast; ignore errors &ast;/
  96  *   /&ast; no error occurred &ast;/ ;
  97  * else
  98  *   /&ast; error &ast;/ ;
  99  * ]|
 100  *
 101  * The #GError object contains three fields: <literal>domain</literal>
 102  * indicates the module the error-reporting function is located in,
 103  * <literal>code</literal> indicates the specific error that occurred,
 104  * and <literal>message</literal> is a user-readable error message with
 105  * as many details as possible. Several functions are provided to deal
 106  * with an error received from a called function: g_error_matches()
 107  * returns %TRUE if the error matches a given domain and code,
 108  * g_propagate_error() copies an error into an error location (so the
 109  * calling function will receive it), and g_clear_error() clears an
 110  * error location by freeing the error and resetting the location to
 111  * %NULL. To display an error to the user, simply display
 112  * <literal>error-&gt;message</literal>, perhaps along with additional
 113  * context known only to the calling function (the file being opened,
 114  * or whatever -- though in the g_file_get_contents() case,
 115  * <literal>error-&gt;message</literal> already contains a filename).
 116  *
 117  * When implementing a function that can report errors, the basic
 118  * tool is g_set_error(). Typically, if a fatal error occurs you
 119  * want to g_set_error(), then return immediately. g_set_error()
 120  * does nothing if the error location passed to it is %NULL.
 121  * Here's an example:
 122  * |[
 123  * gint
 124  * foo_open_file (GError **error)
 125  * {
 126  *   gint fd;
 127  *
 128  *   fd = open ("file.txt", O_RDONLY);
 129  *
 130  *   if (fd &lt; 0)
 131  *     {
 132  *       g_set_error (error,
 133  *                    FOO_ERROR,                 /&ast; error domain &ast;/
 134  *                    FOO_ERROR_BLAH,            /&ast; error code &ast;/
 135  *                    "Failed to open file: &percnt;s", /&ast; error message format string &ast;/
 136  *                    g_strerror (errno));
 137  *       return -1;
 138  *     }
 139  *   else
 140  *     return fd;
 141  * }
 142  * ]|
 143  *
 144  * Things are somewhat more complicated if you yourself call another
 145  * function that can report a #GError. If the sub-function indicates
 146  * fatal errors in some way other than reporting a #GError, such as
 147  * by returning %TRUE on success, you can simply do the following:
 148  * |[
 149  * gboolean
 150  * my_function_that_can_fail (GError **err)
 151  * {
 152  *   g_return_val_if_fail (err == NULL || *err == NULL, FALSE);
 153  *
 154  *   if (!sub_function_that_can_fail (err))
 155  *     {
 156  *       /&ast; assert that error was set by the sub-function &ast;/
 157  *       g_assert (err == NULL || *err != NULL);
 158  *       return FALSE;
 159  *     }
 160  *
 161  *   /&ast; otherwise continue, no error occurred &ast;/
 162  *   g_assert (err == NULL || *err == NULL);
 163  * }
 164  * ]|
 165  *
 166  * If the sub-function does not indicate errors other than by
 167  * reporting a #GError, you need to create a temporary #GError
 168  * since the passed-in one may be %NULL. g_propagate_error() is
 169  * intended for use in this case.
 170  * |[
 171  * gboolean
 172  * my_function_that_can_fail (GError **err)
 173  * {
 174  *   GError *tmp_error;
 175  *
 176  *   g_return_val_if_fail (err == NULL || *err == NULL, FALSE);
 177  *
 178  *   tmp_error = NULL;
 179  *   sub_function_that_can_fail (&amp;tmp_error);
 180  *
 181  *   if (tmp_error != NULL)
 182  *     {
 183  *       /&ast; store tmp_error in err, if err != NULL,
 184  *        &ast; otherwise call g_error_free() on tmp_error
 185  *        &ast;/
 186  *       g_propagate_error (err, tmp_error);
 187  *       return FALSE;
 188  *     }
 189  *
 190  *   /&ast; otherwise continue, no error occurred &ast;/
 191  * }
 192  * ]|
 193  *
 194  * Error pileups are always a bug. For example, this code is incorrect:
 195  * |[
 196  * gboolean
 197  * my_function_that_can_fail (GError **err)
 198  * {
 199  *   GError *tmp_error;
 200  *
 201  *   g_return_val_if_fail (err == NULL || *err == NULL, FALSE);
 202  *
 203  *   tmp_error = NULL;
 204  *   sub_function_that_can_fail (&amp;tmp_error);
 205  *   other_function_that_can_fail (&amp;tmp_error);
 206  *
 207  *   if (tmp_error != NULL)
 208  *     {
 209  *       g_propagate_error (err, tmp_error);
 210  *       return FALSE;
 211  *     }
 212  * }
 213  * ]|
 214  * <literal>tmp_error</literal> should be checked immediately after
 215  * sub_function_that_can_fail(), and either cleared or propagated
 216  * upward. The rule is: <emphasis>after each error, you must either
 217  * handle the error, or return it to the calling function</emphasis>.
 218  * Note that passing %NULL for the error location is the equivalent
 219  * of handling an error by always doing nothing about it. So the
 220  * following code is fine, assuming errors in sub_function_that_can_fail()
 221  * are not fatal to my_function_that_can_fail():
 222  * |[
 223  * gboolean
 224  * my_function_that_can_fail (GError **err)
 225  * {
 226  *   GError *tmp_error;
 227  *
 228  *   g_return_val_if_fail (err == NULL || *err == NULL, FALSE);
 229  *
 230  *   sub_function_that_can_fail (NULL); /&ast; ignore errors &ast;/
 231  *
 232  *   tmp_error = NULL;
 233  *   other_function_that_can_fail (&amp;tmp_error);
 234  *
 235  *   if (tmp_error != NULL)
 236  *     {
 237  *       g_propagate_error (err, tmp_error);
 238  *       return FALSE;
 239  *     }
 240  * }
 241  * ]|
 242  *
 243  * Note that passing %NULL for the error location
 244  * <emphasis>ignores</emphasis> errors; it's equivalent to
 245  * <literal>try { sub_function_that_can_fail (); } catch (...) {}</literal>
 246  * in C++. It does <emphasis>not</emphasis> mean to leave errors
 247  * unhandled; it means to handle them by doing nothing.
 248  *
 249  * Error domains and codes are conventionally named as follows:
 250  * <itemizedlist>
 251  * <listitem><para>
 252  *   The error domain is called
 253  *   <literal>&lt;NAMESPACE&gt;_&lt;MODULE&gt;_ERROR</literal>,
 254  *   for example %G_SPAWN_ERROR or %G_THREAD_ERROR:
 255  *   |[
 256  * #define G_SPAWN_ERROR g_spawn_error_quark ()
 257  *
 258  * GQuark
 259  * g_spawn_error_quark (void)
 260  * {
 261  *   return g_quark_from_static_string ("g-spawn-error-quark");
 262  * }
 263  *   ]|
 264  * </para></listitem>
 265  * <listitem><para>
 266  *   The quark function for the error domain is called
 267  *   <literal>&lt;namespace&gt;_&lt;module&gt;_error_quark</literal>,
 268  *   for example g_spawn_error_quark() or g_thread_error_quark().
 269  * </para></listitem>
 270  * <listitem><para>
 271  *   The error codes are in an enumeration called
 272  *   <literal>&lt;Namespace&gt;&lt;Module&gt;Error</literal>;
 273  *   for example,#GThreadError or #GSpawnError.
 274  * </para></listitem>
 275  * <listitem><para>
 276  *   Members of the error code enumeration are called
 277  *   <literal>&lt;NAMESPACE&gt;_&lt;MODULE&gt;_ERROR_&lt;CODE&gt;</literal>,
 278  *   for example %G_SPAWN_ERROR_FORK or %G_THREAD_ERROR_AGAIN.
 279  * </para></listitem>
 280  * <listitem><para>
 281  *   If there's a "generic" or "unknown" error code for unrecoverable
 282  *   errors it doesn't make sense to distinguish with specific codes,
 283  *   it should be called <literal>&lt;NAMESPACE&gt;_&lt;MODULE&gt;_ERROR_FAILED</literal>,
 284  *   for example %G_SPAWN_ERROR_FAILED.
 285  * </para></listitem>
 286  * </itemizedlist>
 287  *
 288  * Summary of rules for use of #GError:
 289  * <itemizedlist>
 290  * <listitem><para>
 291  *   Do not report programming errors via #GError.
 292  * </para></listitem>
 293  * <listitem><para>
 294  *   The last argument of a function that returns an error should
 295  *   be a location where a #GError can be placed (i.e. "#GError** error").
 296  *   If #GError is used with varargs, the #GError** should be the last
 297  *   argument before the "...".
 298  * </para></listitem>
 299  * <listitem><para>
 300  *   The caller may pass %NULL for the #GError** if they are not interested
 301  *   in details of the exact error that occurred.
 302  * </para></listitem>
 303  * <listitem><para>
 304  *   If %NULL is passed for the #GError** argument, then errors should
 305  *   not be returned to the caller, but your function should still
 306  *   abort and return if an error occurs. That is, control flow should
 307  *   not be affected by whether the caller wants to get a #GError.
 308  * </para></listitem>
 309  * <listitem><para>
 310  *   If a #GError is reported, then your function by definition
 311  *   <emphasis>had a fatal failure and did not complete whatever
 312  *   it was supposed to do</emphasis>. If the failure was not fatal,
 313  *   then you handled it and you should not report it. If it was fatal,
 314  *   then you must report it and discontinue whatever you were doing
 315  *   immediately.
 316  * </para></listitem>
 317  * <listitem><para>
 318  *   If a #GError is reported, out parameters are not guaranteed to
 319  *   be set to any defined value.
 320  * </para></listitem>
 321  * <listitem><para>
 322  *   A #GError* must be initialized to %NULL before passing its address
 323  *   to a function that can report errors.
 324  * </para></listitem>
 325  * <listitem><para>
 326  *   "Piling up" errors is always a bug. That is, if you assign a
 327  *   new #GError to a #GError* that is non-%NULL, thus overwriting
 328  *   the previous error, it indicates that you should have aborted
 329  *   the operation instead of continuing. If you were able to continue,
 330  *   you should have cleared the previous error with g_clear_error().
 331  *   g_set_error() will complain if you pile up errors.
 332  * </para></listitem>
 333  * <listitem><para>
 334  *   By convention, if you return a boolean value indicating success
 335  *   then %TRUE means success and %FALSE means failure. If %FALSE is
 336  *   returned, the error <emphasis>must</emphasis> be set to a non-%NULL
 337  *   value.
 338  * </para></listitem>
 339  * <listitem><para>
 340  *   A %NULL return value is also frequently used to mean that an error
 341  *   occurred. You should make clear in your documentation whether %NULL
 342  *   is a valid return value in non-error cases; if %NULL is a valid value,
 343  *   then users must check whether an error was returned to see if the
 344  *   function succeeded.
 345  * </para></listitem>
 346  * <listitem><para>
 347  *   When implementing a function that can report errors, you may want
 348  *   to add a check at the top of your function that the error return
 349  *   location is either %NULL or contains a %NULL error (e.g.
 350  *   <literal>g_return_if_fail (error == NULL || *error == NULL);</literal>).
 351  * </para></listitem>
 352  * </itemizedlist>
 353  */
 354
 355 #include "config.h"
 356
 357 #include "gerror.h"
 358
 359 #include "gslice.h"
 360 #include "gstrfuncs.h"
 361 #include "gtestutils.h"
 362
 363 /**
 364  * g_error_new_valist:
 365  * @domain: error domain
 366  * @code: error code
 367  * @format: printf()-style format for error message
 368  * @args: #va_list of parameters for the message format
 369  *
 370  * Creates a new #GError with the given @domain and @code,
 371  * and a message formatted with @format.
 372  *
 373  * Returns: a new #GError
 374  *
 375  * Since: 2.22
 376  */
 377 GError*
 378 g_error_new_valist (GQuark       domain,
 379                     gint         code,
 380                     const gchar *format,
 381                     va_list      args)
 382 {
 383   GError *error;
 384
 385   /* Historically, GError allowed this (although it was never meant to work),
 386    * and it has significant use in the wild, which g_return_val_if_fail
 387    * would break. It should maybe g_return_val_if_fail in GLib 4.
 388    * (GNOME#660371, GNOME#560482)
 389    */
 390   g_warn_if_fail (domain != 0);
 391   g_warn_if_fail (format != NULL);
 392
 393   error = g_slice_new (GError);
 394
 395   error->domain = domain;
 396   error->code = code;
 397   error->message = g_strdup_vprintf (format, args);
 398
 399   return error;
 400 }
 401
 402 /**
 403  * g_error_new:
 404  * @domain: error domain
 405  * @code: error code
 406  * @format: printf()-style format for error message
 407  * @...: parameters for message format
 408  *
 409  * Creates a new #GError with the given @domain and @code,
 410  * and a message formatted with @format.
 411  *
 412  * Return value: a new #GError
 413  */
 414 GError*
 415 g_error_new (GQuark       domain,
 416              gint         code,
 417              const gchar *format,
 418              ...)
 419 {
 420   GError* error;
 421   va_list args;
 422
 423   g_return_val_if_fail (format != NULL, NULL);
 424   g_return_val_if_fail (domain != 0, NULL);
 425
 426   va_start (args, format);
 427   error = g_error_new_valist (domain, code, format, args);
 428   va_end (args);
 429
 430   return error;
 431 }
 432
 433 /**
 434  * g_error_new_literal:
 435  * @domain: error domain
 436  * @code: error code
 437  * @message: error message
 438  *
 439  * Creates a new #GError; unlike g_error_new(), @message is
 440  * not a printf()-style format string. Use this function if
 441  * @message contains text you don't have control over,
 442  * that could include printf() escape sequences.
 443  *
 444  * Return value: a new #GError
 445  **/
 446 GError*
 447 g_error_new_literal (GQuark         domain,
 448                      gint           code,
 449                      const gchar   *message)
 450 {
 451   GError* err;
 452
 453   g_return_val_if_fail (message != NULL, NULL);
 454   g_return_val_if_fail (domain != 0, NULL);
 455
 456   err = g_slice_new (GError);
 457
 458   err->domain = domain;
 459   err->code = code;
 460   err->message = g_strdup (message);
 461
 462   return err;
 463 }
 464
 465 /**
 466  * g_error_free:
 467  * @error: a #GError
 468  *
 469  * Frees a #GError and associated resources.
 470  */
 471 void
 472 g_error_free (GError *error)
 473 {
 474   g_return_if_fail (error != NULL);
 475
 476   g_free (error->message);
 477
 478   g_slice_free (GError, error);
 479 }
 480
 481 /**
 482  * g_error_copy:
 483  * @error: a #GError
 484  *
 485  * Makes a copy of @error.
 486  *
 487  * Return value: a new #GError
 488  */
 489 GError*
 490 g_error_copy (const GError *error)
 491 {
 492   GError *copy;
 493
 494   g_return_val_if_fail (error != NULL, NULL);
 495   /* See g_error_new_valist for why these don't return */
 496   g_warn_if_fail (error->domain != 0);
 497   g_warn_if_fail (error->message != NULL);
 498
 499   copy = g_slice_new (GError);
 500
 501   *copy = *error;
 502
 503   copy->message = g_strdup (error->message);
 504
 505   return copy;
 506 }
 507
 508 /**
 509  * g_error_matches:
 510  * @error: (allow-none): a #GError or %NULL
 511  * @domain: an error domain
 512  * @code: an error code
 513  *
 514  * Returns %TRUE if @error matches @domain and @code, %FALSE
 515  * otherwise. In particular, when @error is %NULL, %FALSE will
 516  * be returned.
 517  *
 518  * Return value: whether @error has @domain and @code
 519  */
 520 gboolean
 521 g_error_matches (const GError *error,
 522                  GQuark        domain,
 523                  gint          code)
 524 {
 525   return error &&
 526     error->domain == domain &&
 527     error->code == code;
 528 }
 529
 530 #define ERROR_OVERWRITTEN_WARNING "GError set over the top of a previous GError or uninitialized memory.\n" \
 531                "This indicates a bug in someone's code. You must ensure an error is NULL before it's set.\n" \
 532                "The overwriting error message was: %s"
 533
 534 /**
 535  * g_set_error:
 536  * @err: (allow-none): a return location for a #GError, or %NULL
 537  * @domain: error domain
 538  * @code: error code
 539  * @format: printf()-style format
 540  * @...: args for @format
 541  *
 542  * Does nothing if @err is %NULL; if @err is non-%NULL, then *@err
 543  * must be %NULL. A new #GError is created and assigned to *@err.
 544  */
 545 void
 546 g_set_error (GError      **err,
 547              GQuark        domain,
 548              gint          code,
 549              const gchar  *format,
 550              ...)
 551 {
 552   GError *new;
 553
 554   va_list args;
 555
 556   if (err == NULL)
 557     return;
 558
 559   va_start (args, format);
 560   new = g_error_new_valist (domain, code, format, args);
 561   va_end (args);
 562
 563   if (*err == NULL)
 564     *err = new;
 565   else
 566     g_warning (ERROR_OVERWRITTEN_WARNING, new->message);
 567 }
 568
 569 /**
 570  * g_set_error_literal:
 571  * @err: (allow-none): a return location for a #GError, or %NULL
 572  * @domain: error domain
 573  * @code: error code
 574  * @message: error message
 575  *
 576  * Does nothing if @err is %NULL; if @err is non-%NULL, then *@err
 577  * must be %NULL. A new #GError is created and assigned to *@err.
 578  * Unlike g_set_error(), @message is not a printf()-style format string.
 579  * Use this function if @message contains text you don't have control over,
 580  * that could include printf() escape sequences.
 581  *
 582  * Since: 2.18
 583  */
 584 void
 585 g_set_error_literal (GError      **err,
 586                      GQuark        domain,
 587                      gint          code,
 588                      const gchar  *message)
 589 {
 590   GError *new;
 591
 592   if (err == NULL)
 593     return;
 594
 595   new = g_error_new_literal (domain, code, message);
 596   if (*err == NULL)
 597     *err = new;
 598   else
 599     g_warning (ERROR_OVERWRITTEN_WARNING, new->message);
 600 }
 601
 602 /**
 603  * g_propagate_error:
 604  * @dest: error return location
 605  * @src: error to move into the return location
 606  *
 607  * If @dest is %NULL, free @src; otherwise, moves @src into *@dest.
 608  * The error variable @dest points to must be %NULL.
 609  */
 610 void
 611 g_propagate_error (GError **dest,
 612                    GError  *src)
 613 {
 614   g_return_if_fail (src != NULL);
 615
 616   if (dest == NULL)
 617     {
 618       if (src)
 619         g_error_free (src);
 620       return;
 621     }
 622   else
 623     {
 624       if (*dest != NULL)
 625         g_warning (ERROR_OVERWRITTEN_WARNING, src->message);
 626       else
 627         *dest = src;
 628     }
 629 }
 630
 631 /**
 632  * g_clear_error:
 633  * @err: a #GError return location
 634  *
 635  * If @err is %NULL, does nothing. If @err is non-%NULL,
 636  * calls g_error_free() on *@err and sets *@err to %NULL.
 637  */
 638 void
 639 g_clear_error (GError **err)
 640 {
 641   if (err && *err)
 642     {
 643       g_error_free (*err);
 644       *err = NULL;
 645     }
 646 }
 647
 648 static void
 649 g_error_add_prefix (gchar       **string,
 650                     const gchar  *format,
 651                     va_list       ap)
 652 {
 653   gchar *oldstring;
 654   gchar *prefix;
 655
 656   prefix = g_strdup_vprintf (format, ap);
 657   oldstring = *string;
 658   *string = g_strconcat (prefix, oldstring, NULL);
 659   g_free (oldstring);
 660   g_free (prefix);
 661 }
 662
 663 /**
 664  * g_prefix_error:
 665  * @err: (allow-none): a return location for a #GError, or %NULL
 666  * @format: printf()-style format string
 667  * @...: arguments to @format
 668  *
 669  * Formats a string according to @format and
 670  * prefix it to an existing error message.  If
 671  * @err is %NULL (ie: no error variable) then do
 672  * nothing.
 673  *
 674  * If *@err is %NULL (ie: an error variable is
 675  * present but there is no error condition) then
 676  * also do nothing.  Whether or not it makes
 677  * sense to take advantage of this feature is up
 678  * to you.
 679  *
 680  * Since: 2.16
 681  */
 682 void
 683 g_prefix_error (GError      **err,
 684                 const gchar  *format,
 685                 ...)
 686 {
 687   if (err && *err)
 688     {
 689       va_list ap;
 690
 691       va_start (ap, format);
 692       g_error_add_prefix (&(*err)->message, format, ap);
 693       va_end (ap);
 694     }
 695 }
 696
 697 /**
 698  * g_propagate_prefixed_error:
 699  * @dest: error return location
 700  * @src: error to move into the return location
 701  * @format: printf()-style format string
 702  * @...: arguments to @format
 703  *
 704  * If @dest is %NULL, free @src; otherwise,
 705  * moves @src into *@dest. *@dest must be %NULL.
 706  * After the move, add a prefix as with
 707  * g_prefix_error().
 708  *
 709  * Since: 2.16
 710  **/
 711 void
 712 g_propagate_prefixed_error (GError      **dest,
 713                             GError       *src,
 714                             const gchar  *format,
 715                             ...)
 716 {
 717   g_propagate_error (dest, src);
 718
 719   if (dest && *dest)
 720     {
 721       va_list ap;
 722
 723       va_start (ap, format);
 724       g_error_add_prefix (&(*dest)->message, format, ap);
 725       va_end (ap);
 726     }
 727 }