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  39. <tr><td colspan="5" class="shortcuts"><nobr><a href="#glib-Error-Reporting.synopsis" class="shortcut">Top</a>
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  40.                    | 
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  41.                   <a href="#glib-Error-Reporting.description" class="shortcut">Description</a></nobr></td></tr>
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    43. 

  43. <div class="refentry" lang="en">
    44. 

  44. <a name="glib-Error-Reporting"></a><div class="titlepage"></div>
    45. 

  45. <div class="refnamediv"><table width="100%"><tr>
    46. 

  46. <td valign="top">
    47. 

  47. <h2><span class="refentrytitle"><a name="glib-Error-Reporting.top_of_page"></a>Error Reporting</span></h2>
    48. 

  48. <p>Error Reporting — a system for reporting errors</p>
    49. 

  49. </td>
    50. 

  50. <td valign="top" align="right"></td>
    51. 

  51. </tr></table></div>
    52. 

  52. <div class="refsynopsisdiv">
    53. 

  53. <a name="glib-Error-Reporting.synopsis"></a><h2>Synopsis</h2>
    54. 

  54. <pre class="synopsis">
    55. 

  55. 

  56. #include &lt;glib.h&gt;
    57. 

  57. 

  58.                     <a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a>;
    59. 

  59. <a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a>*             <a class="link" href="glib-Error-Reporting.html#g-error-new" title="g_error_new ()">g_error_new</a>                         (<a class="link" href="glib-Quarks.html#GQuark" title="GQuark">GQuark</a> domain,
    60. 

  60.                                                          <a class="link" href="glib-Basic-Types.html#gint" title="gint">gint</a> code,
    61. 

  61.                                                          const <a class="link" href="glib-Basic-Types.html#gchar" title="gchar">gchar</a> *format,
    62. 

  62.                                                          ...);
    63. 

  63. <a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a>*             <a class="link" href="glib-Error-Reporting.html#g-error-new-literal" title="g_error_new_literal ()">g_error_new_literal</a>                 (<a class="link" href="glib-Quarks.html#GQuark" title="GQuark">GQuark</a> domain,
    64. 

  64.                                                          <a class="link" href="glib-Basic-Types.html#gint" title="gint">gint</a> code,
    65. 

  65.                                                          const <a class="link" href="glib-Basic-Types.html#gchar" title="gchar">gchar</a> *message);
    66. 

  66. void                <a class="link" href="glib-Error-Reporting.html#g-error-free" title="g_error_free ()">g_error_free</a>                        (<a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> *error);
    67. 

  67. <a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a>*             <a class="link" href="glib-Error-Reporting.html#g-error-copy" title="g_error_copy ()">g_error_copy</a>                        (const <a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> *error);
    68. 

  68. <a class="link" href="glib-Basic-Types.html#gboolean" title="gboolean">gboolean</a>            <a class="link" href="glib-Error-Reporting.html#g-error-matches" title="g_error_matches ()">g_error_matches</a>                     (const <a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> *error,
    69. 

  69.                                                          <a class="link" href="glib-Quarks.html#GQuark" title="GQuark">GQuark</a> domain,
    70. 

  70.                                                          <a class="link" href="glib-Basic-Types.html#gint" title="gint">gint</a> code);
    71. 

  71. void                <a class="link" href="glib-Error-Reporting.html#g-set-error" title="g_set_error ()">g_set_error</a>                         (<a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> **err,
    72. 

  72.                                                          <a class="link" href="glib-Quarks.html#GQuark" title="GQuark">GQuark</a> domain,
    73. 

  73.                                                          <a class="link" href="glib-Basic-Types.html#gint" title="gint">gint</a> code,
    74. 

  74.                                                          const <a class="link" href="glib-Basic-Types.html#gchar" title="gchar">gchar</a> *format,
    75. 

  75.                                                          ...);
    76. 

  76. void                <a class="link" href="glib-Error-Reporting.html#g-propagate-error" title="g_propagate_error ()">g_propagate_error</a>                   (<a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> **dest,
    77. 

  77.                                                          <a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> *src);
    78. 

  78. void                <a class="link" href="glib-Error-Reporting.html#g-clear-error" title="g_clear_error ()">g_clear_error</a>                       (<a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> **err);
    79. 

  79. void                <a class="link" href="glib-Error-Reporting.html#g-prefix-error" title="g_prefix_error ()">g_prefix_error</a>                      (<a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> **err,
    80. 

  80.                                                          const <a class="link" href="glib-Basic-Types.html#gchar" title="gchar">gchar</a> *format,
    81. 

  81.                                                          ...);
    82. 

  82. void                <a class="link" href="glib-Error-Reporting.html#g-propagate-prefixed-error" title="g_propagate_prefixed_error ()">g_propagate_prefixed_error</a>          (<a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> **dest,
    83. 

  83.                                                          <a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> *src,
    84. 

  84.                                                          const <a class="link" href="glib-Basic-Types.html#gchar" title="gchar">gchar</a> *format,
    85. 

  85.                                                          ...);
    86. 

  86. </pre>
    87. 

  87. </div>
    88. 

  88. <div class="refsect1" lang="en">
    89. 

  89. <a name="glib-Error-Reporting.description"></a><h2>Description</h2>
    90. 

  90. <p>
    91. 

  91. GLib provides a standard method of reporting errors from a called function to
    92. 

  92. the calling code. (This is the same problem solved by exceptions in other
    93. 

  93. languages.) It's important to understand that this method is both a
    94. 

  94. <span class="emphasis"><em>data type</em></span> (the <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a> object) and a <span class="emphasis"><em>set of
    95. 

  95. rules.</em></span> If you use <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a> incorrectly, then your code will not
    96. 

  96. properly interoperate with other code that uses <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>, and users of your API
    97. 

  97. will probably get confused.
    98. 

  98. </p>
    99. 

  99. <p>
    100. 

  100. First and foremost: <span class="emphasis"><em><a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a> should only be used to report
    101. 

  101. recoverable runtime errors, never to report programming errors.</em></span> If
    102. 

  102. the programmer has screwed up, then you should use <a class="link" href="glib-Message-Logging.html#g-warning" title="g_warning()"><code class="function">g_warning()</code></a>,
    103. 

  103. <a class="link" href="glib-Warnings-and-Assertions.html#g-return-if-fail" title="g_return_if_fail()"><code class="function">g_return_if_fail()</code></a>, <a class="link" href="glib-Testing.html#g-assert" title="g_assert()"><code class="function">g_assert()</code></a>, <a class="link" href="glib-Message-Logging.html#g-error" title="g_error()"><code class="function">g_error()</code></a>, or some similar facility.
    104. 

  104. (Incidentally, remember that the <a class="link" href="glib-Message-Logging.html#g-error" title="g_error()"><code class="function">g_error()</code></a> function should
    105. 

  105. <span class="emphasis"><em>only</em></span> be used for programming errors, it should not be used
    106. 

  106. to print any error reportable via <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>.)
    107. 

  107. </p>
    108. 

  108. <p>
    109. 

  109. Examples of recoverable runtime errors are "file not found" or "failed to parse
    110. 

  110. input." Examples of programming errors are "NULL passed to <code class="function">strcmp()</code>" or
    111. 

  111. "attempted to free the same pointer twice." These two kinds of errors are
    112. 

  112. fundamentally different: runtime errors should be handled or reported to the
    113. 

  113. user, programming errors should be eliminated by fixing the bug in the program.
    114. 

  114. This is why most functions in GLib and GTK+ do not use the <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a> facility.
    115. 

  115. </p>
    116. 

  116. <p>
    117. 

  117. Functions that can fail take a return location for a <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a> as their last argument. 
    118. 

  118. For example:
    119. 

  119. </p>
    120. 

  120. <div class="informalexample"><pre class="programlisting">
    121. 

  121. gboolean g_file_get_contents (const gchar *filename, 
    122. 

  122. 	                      gchar      **contents,
    123. 

  123.                               gsize       *length,
    124. 

  124.                               GError     **error);
    125. 

  125. </pre></div>
    126. 

  126. <p>
    127. 

  127. If you pass a non-<a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a> value for the <code class="literal">error</code> argument, it should 
    128. 

  128. point to a location where an error can be placed. For example:
    129. 

  129. </p>
    130. 

  130. <div class="informalexample"><pre class="programlisting">
    131. 

  131. gchar *contents;
    132. 

  132. GError *err = NULL;
    133. 

  133. g_file_get_contents ("foo.txt", &amp;contents, NULL, &amp;err);
    134. 

  134. g_assert ((contents == NULL &amp;&amp; err != NULL) || (contents != NULL &amp;&amp; err == NULL));
    135. 

  135. if (err != NULL)
    136. 

  136.   {
    137. 

  137.     /* Report error to user, and free error */
    138. 

  138.     g_assert (contents == NULL);
    139. 

  139.     fprintf (stderr, "Unable to read file: %s\n", err-&gt;message);
    140. 

  140.     g_error_free (err);
    141. 

  141.   } 
    142. 

  142. else
    143. 

  143.   {
    144. 

  144.     /* Use file contents */
    145. 

  145.     g_assert (contents != NULL);
    146. 

  146.   }
    147. 

  147. </pre></div>
    148. 

  148. <p>
    149. 

  149. Note that <code class="literal">err != NULL</code> in this example is a
    150. 

  150. <span class="emphasis"><em>reliable</em></span> indicator of whether
    151. 

  151. <a class="link" href="glib-File-Utilities.html#g-file-get-contents" title="g_file_get_contents ()"><code class="function">g_file_get_contents()</code></a> failed. Additionally, <a class="link" href="glib-File-Utilities.html#g-file-get-contents" title="g_file_get_contents ()"><code class="function">g_file_get_contents()</code></a> returns
    152. 

  152. a boolean which indicates whether it was successful.
    153. 

  153. </p>
    154. 

  154. <p>
    155. 

  155. Because <a class="link" href="glib-File-Utilities.html#g-file-get-contents" title="g_file_get_contents ()"><code class="function">g_file_get_contents()</code></a> returns <a class="link" href="glib-Standard-Macros.html#FALSE:CAPS" title="FALSE"><code class="literal">FALSE</code></a> on failure, if you are only
    156. 

  156. interested in whether it failed and don't need to display an error message, you
    157. 

  157. can pass <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a> for the <code class="literal">error</code> argument:
    158. 

  158. </p>
    159. 

  159. <div class="informalexample"><pre class="programlisting">
    160. 

  160. if (g_file_get_contents ("foo.txt", &amp;contents, NULL, NULL)) /* ignore errors */
    161. 

  161.   /* no error occurred */ ;
    162. 

  162. else
    163. 

  163.   /* error */ ;
    164. 

  164. </pre></div>
    165. 

  165. <p>
    166. 

  166. </p>
    167. 

  167. <p>
    168. 

  168. The <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a> object contains three fields: <code class="literal">domain</code> indicates
    169. 

  169. the module the error-reporting function is located in, <code class="literal">code</code>
    170. 

  170. indicates the specific error that occurred, and <code class="literal">message</code> is a
    171. 

  171. user-readable error message with as many details as possible. Several functions
    172. 

  172. are provided to deal with an error received from a called function:
    173. 

  173. <a class="link" href="glib-Error-Reporting.html#g-error-matches" title="g_error_matches ()"><code class="function">g_error_matches()</code></a> returns <a class="link" href="glib-Standard-Macros.html#TRUE:CAPS" title="TRUE"><code class="literal">TRUE</code></a> if the error matches a given domain and code,
    174. 

  174. <a class="link" href="glib-Error-Reporting.html#g-propagate-error" title="g_propagate_error ()"><code class="function">g_propagate_error()</code></a> copies an error into an error location (so the calling
    175. 

  175. function will receive it), and <a class="link" href="glib-Error-Reporting.html#g-clear-error" title="g_clear_error ()"><code class="function">g_clear_error()</code></a> clears an error location by
    176. 

  176. freeing the error and resetting the location to <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a>. To display an error to the
    177. 

  177. user, simply display <code class="literal">error-&gt;message</code>, perhaps along with
    178. 

  178. additional context known only to the calling function (the file being opened, or
    179. 

  179. whatever -- though in the <a class="link" href="glib-File-Utilities.html#g-file-get-contents" title="g_file_get_contents ()"><code class="function">g_file_get_contents()</code></a> case,
    180. 

  180. <code class="literal">error-&gt;message</code> already contains a filename).
    181. 

  181. </p>
    182. 

  182. <p>
    183. 

  183. When implementing a function that can report errors, the basic tool is
    184. 

  184. <a class="link" href="glib-Error-Reporting.html#g-set-error" title="g_set_error ()"><code class="function">g_set_error()</code></a>. Typically, if a fatal error occurs you want to <a class="link" href="glib-Error-Reporting.html#g-set-error" title="g_set_error ()"><code class="function">g_set_error()</code></a>,
    185. 

  185. then return immediately. <a class="link" href="glib-Error-Reporting.html#g-set-error" title="g_set_error ()"><code class="function">g_set_error()</code></a> does nothing if the error location passed
    186. 

  186. to it is <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a>. Here's an example:
    187. 

  187. </p>
    188. 

  188. <div class="informalexample"><pre class="programlisting">
    189. 

  189. gint
    190. 

  190. foo_open_file (GError **error)
    191. 

  191. {
    192. 

  192.   gint fd;
    193. 

  193. 

  194.   fd = open ("file.txt", O_RDONLY);
    195. 

  195. 

  196.   if (fd &lt; 0)
    197. 

  197.     {
    198. 

  198.       g_set_error (error,
    199. 

  199.                    FOO_ERROR,                 /* error domain */
    200. 

  200.                    FOO_ERROR_BLAH,            /* error code */
    201. 

  201.                    "Failed to open file: %s", /* error message format string */
    202. 

  202.                    g_strerror (errno));
    203. 

  203.       return -1;
    204. 

  204.     }
    205. 

  205.   else
    206. 

  206.     return fd;
    207. 

  207. }
    208. 

  208. </pre></div>
    209. 

  209. <p>
    210. 

  210. </p>
    211. 

  211. <p>
    212. 

  212. Things are somewhat more complicated if you yourself call another function that
    213. 

  213. can report a <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>. If the sub-function indicates fatal errors in some way
    214. 

  214. other than reporting a <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>, such as by returning <a class="link" href="glib-Standard-Macros.html#TRUE:CAPS" title="TRUE"><code class="literal">TRUE</code></a> on success, you can
    215. 

  215. simply do the following:
    216. 

  216. </p>
    217. 

  217. <div class="informalexample"><pre class="programlisting">
    218. 

  218. gboolean
    219. 

  219. my_function_that_can_fail (GError **err)
    220. 

  220. {
    221. 

  221.   g_return_val_if_fail (err == NULL || *err == NULL, FALSE);
    222. 

  222. 

  223.   if (!sub_function_that_can_fail (err))
    224. 

  224.     {
    225. 

  225.        /* assert that error was set by the sub-function */
    226. 

  226.        g_assert (err == NULL || *err != NULL);  
    227. 

  227.        return FALSE;
    228. 

  228.     }
    229. 

  229. 

  230.   /* otherwise continue, no error occurred */
    231. 

  231.   g_assert (err == NULL || *err == NULL);
    232. 

  232. }
    233. 

  233. </pre></div>
    234. 

  234. <p>
    235. 

  235. </p>
    236. 

  236. <p>
    237. 

  237. If the sub-function does not indicate errors other than by reporting a <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>, 
    238. 

  238. you need to create a temporary <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a> since the passed-in one may be <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a>.
    239. 

  239. <a class="link" href="glib-Error-Reporting.html#g-propagate-error" title="g_propagate_error ()"><code class="function">g_propagate_error()</code></a> is intended for use in this case.
    240. 

  240. </p>
    241. 

  241. <div class="informalexample"><pre class="programlisting">
    242. 

  242. gboolean
    243. 

  243. my_function_that_can_fail (GError **err)
    244. 

  244. {
    245. 

  245.   GError *tmp_error;
    246. 

  246. 

  247.   g_return_val_if_fail (err == NULL || *err == NULL, FALSE);
    248. 

  248. 

  249.   tmp_error = NULL;
    250. 

  250.   sub_function_that_can_fail (&amp;tmp_error);
    251. 

  251. 

  252.   if (tmp_error != NULL)
    253. 

  253.     {
    254. 

  254.        /* store tmp_error in err, if err != NULL,
    255. 

  255.         * otherwise call g_error_free() on tmp_error 
    256. 

  256.         */
    257. 

  257.        g_propagate_error (err, tmp_error);
    258. 

  258.        return FALSE;
    259. 

  259.     }
    260. 

  260. 

  261.   /* otherwise continue, no error occurred */
    262. 

  262. }
    263. 

  263. </pre></div>
    264. 

  264. <p>
    265. 

  265. </p>
    266. 

  266. <p>
    267. 

  267. Error pileups are always a bug. For example, this code is incorrect:
    268. 

  268. </p>
    269. 

  269. <div class="informalexample"><pre class="programlisting">
    270. 

  270. gboolean
    271. 

  271. my_function_that_can_fail (GError **err)
    272. 

  272. {
    273. 

  273.   GError *tmp_error;
    274. 

  274. 

  275.   g_return_val_if_fail (err == NULL || *err == NULL, FALSE);
    276. 

  276. 

  277.   tmp_error = NULL;
    278. 

  278.   sub_function_that_can_fail (&amp;tmp_error);
    279. 

  279.   other_function_that_can_fail (&amp;tmp_error);
    280. 

  280. 

  281.   if (tmp_error != NULL)
    282. 

  282.     {
    283. 

  283.        g_propagate_error (err, tmp_error);
    284. 

  284.        return FALSE;
    285. 

  285.     }
    286. 

  286. }
    287. 

  287. </pre></div>
    288. 

  288. <p>
    289. 

  289. <code class="literal">tmp_error</code> should be checked immediately after
    290. 

  290. <code class="function"><code class="function">sub_function_that_can_fail()</code></code>, and either cleared or propagated upward.  The rule
    291. 

  291. is: <span class="emphasis"><em>after each error, you must either handle the error, or return it to the
    292. 

  292. calling function</em></span>.  Note that passing <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a> for the error location is the
    293. 

  293. equivalent of handling an error by always doing nothing about it. So the
    294. 

  294. following code is fine, assuming errors in <code class="function"><code class="function">sub_function_that_can_fail()</code></code> are not
    295. 

  295. fatal to <code class="function"><code class="function">my_function_that_can_fail()</code></code>:
    296. 

  296. </p>
    297. 

  297. <div class="informalexample"><pre class="programlisting">
    298. 

  298. gboolean
    299. 

  299. my_function_that_can_fail (GError **err)
    300. 

  300. {
    301. 

  301.   GError *tmp_error;
    302. 

  302. 

  303.   g_return_val_if_fail (err == NULL || *err == NULL, FALSE);
    304. 

  304. 

  305.   sub_function_that_can_fail (NULL); /* ignore errors */
    306. 

  306. 

  307.   tmp_error = NULL;
    308. 

  308.   other_function_that_can_fail (&amp;tmp_error);
    309. 

  309. 

  310.   if (tmp_error != NULL)
    311. 

  311.     {
    312. 

  312.        g_propagate_error (err, tmp_error);
    313. 

  313.        return FALSE;
    314. 

  314.     }
    315. 

  315. }
    316. 

  316. </pre></div>
    317. 

  317. <p>
    318. 

  318. </p>
    319. 

  319. <p>
    320. 

  320. Note that passing <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a> for the error location <span class="emphasis"><em>ignores</em></span>
    321. 

  321. errors; it's equivalent to <code class="literal">try { <code class="function">sub_function_that_can_fail()</code>; } catch
    322. 

  322. (...) {}</code> in C++. It does <span class="emphasis"><em>not</em></span> mean to leave errors
    323. 

  323. unhandled; it means to handle them by doing nothing.
    324. 

  324. </p>
    325. 

  325. <p>
    326. 

  326. Error domains and codes are conventionally named as follows:
    327. 

  327. </p>
    328. 

  328. <div class="itemizedlist"><ul type="disc">
    329. 

  329. <li>
    330. 

  330. <p>
    331. 

  331. The error domain is called 
    332. 

  332. <code class="literal">&lt;NAMESPACE&gt;_&lt;MODULE&gt;_ERROR</code>, for example
    333. 

  333. <a class="link" href="glib-Spawning-Processes.html#G-SPAWN-ERROR:CAPS" title="G_SPAWN_ERROR"><code class="literal">G_SPAWN_ERROR</code></a> or <a class="link" href="glib-Threads.html#G-THREAD-ERROR:CAPS" title="G_THREAD_ERROR"><code class="literal">G_THREAD_ERROR</code></a>:
    334. 

  334. </p>
    335. 

  335. <div class="informalexample"><pre class="programlisting">
    336. 

  336. #define G_SPAWN_ERROR g_spawn_error_quark ()
    337. 

  337. 

  338. GQuark
    339. 

  339. g_spawn_error_quark (void)
    340. 

  340. {
    341. 

  341.   return g_quark_from_static_string ("g-spawn-error-quark");
    342. 

  342. }
    343. 

  343. </pre></div>
    344. 

  344. <p>
    345. 

  345. </p>
    346. 

  346. </li>
    347. 

  347. <li><p>
    348. 

  348. The error codes are in an enumeration called 
    349. 

  349. <code class="literal">&lt;Namespace&gt;&lt;Module&gt;Error</code>; for example,
    350. 

  350. <a class="link" href="glib-Threads.html#GThreadError" title="enum GThreadError"><span class="type">GThreadError</span></a> or <a class="link" href="glib-Spawning-Processes.html#GSpawnError" title="enum GSpawnError"><span class="type">GSpawnError</span></a>.
    351. 

  351. </p></li>
    352. 

  352. <li><p>
    353. 

  353. Members of the error code enumeration are called <code class="literal">&lt;NAMESPACE&gt;_&lt;MODULE&gt;_ERROR_&lt;CODE&gt;</code>, for example <a class="link" href="glib-Spawning-Processes.html#G-SPAWN-ERROR-FORK:CAPS"><code class="literal">G_SPAWN_ERROR_FORK</code></a> or <a class="link" href="glib-Threads.html#G-THREAD-ERROR-AGAIN:CAPS"><code class="literal">G_THREAD_ERROR_AGAIN</code></a>. 
    354. 

  354. </p></li>
    355. 

  355. <li><p>
    356. 

  356. If there's a "generic" or "unknown" error code for unrecoverable errors it
    357. 

  357. doesn't make sense to distinguish with specific codes, it should be called 
    358. 

  358. <code class="literal">&lt;NAMESPACE&gt;_&lt;MODULE&gt;_ERROR_FAILED</code>, for 
    359. 

  359. example <a class="link" href="glib-Spawning-Processes.html#G-SPAWN-ERROR-FAILED:CAPS"><code class="literal">G_SPAWN_ERROR_FAILED</code></a> or <code class="literal">G_THREAD_ERROR_FAILED</code>.
    360. 

  360. </p></li>
    361. 

  361. </ul></div>
    362. 

  362. <p>
    363. 

  363. </p>
    364. 

  364. <p>
    365. 

  365. Summary of rules for use of <span class="type">""</span>
    366. 

  366.       </p>
    367. 

  367. <div class="itemizedlist"><ul type="disc">
    368. 

  368. <li><p>
    369. 

  369.            Do not report programming errors via <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>.
    370. 

  370. 	  </p></li>
    371. 

  371. <li><p>
    372. 

  372.           The last argument of a function that returns an error should be a
    373. 

  373.           location where a <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a> can be placed (i.e. "<a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>** error").  If
    374. 

  374.           <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a> is used with varargs, the <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>** should be the last
    375. 

  375.           argument before the "...".
    376. 

  376.         </p></li>
    377. 

  377. <li><p>
    378. 

  378.           The caller may pass <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a> for the <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>** if they are not interested
    379. 

  379.           in details of the exact error that occurred.
    380. 

  380.         </p></li>
    381. 

  381. <li><p>
    382. 

  382.            If <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a> is passed for the <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>** argument, then errors should 
    383. 

  383.            not be returned to the caller, but your function should still 
    384. 

  384.            abort and return if an error occurs. That is, control flow should
    385. 

  385.            not be affected by whether the caller wants to get a <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>.
    386. 

  386. 	  </p></li>
    387. 

  387. <li><p>
    388. 

  388.           If a <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a> is reported, then your function by definition  
    389. 

  389.           <span class="emphasis"><em>had a fatal failure and did not complete whatever it was supposed
    390. 

  390.             to do</em></span>. If the failure was not fatal, then you handled it
    391. 

  391.           and you should not report it. If it was fatal, then you must report it 
    392. 

  392.           and discontinue whatever you were doing immediately.
    393. 

  393.         </p></li>
    394. 

  394. <li><p>
    395. 

  395.           A <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>* must be initialized to <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a> before passing its address to
    396. 

  396.           a function that can report errors.
    397. 

  397. 	  </p></li>
    398. 

  398. <li><p>
    399. 

  399.           "Piling up" errors is always a bug. That is, if you assign a new
    400. 

  400.           <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a> to a <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>* that is non-<a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a>, thus overwriting the previous
    401. 

  401.           error, it indicates that you should have aborted the operation instead
    402. 

  402.           of continuing. If you were able to continue, you should have cleared
    403. 

  403.           the previous error with <a class="link" href="glib-Error-Reporting.html#g-clear-error" title="g_clear_error ()"><code class="function">g_clear_error()</code></a>. <a class="link" href="glib-Error-Reporting.html#g-set-error" title="g_set_error ()"><code class="function">g_set_error()</code></a> will complain
    404. 

  404.           if you pile up errors.
    405. 

  405. 	  </p></li>
    406. 

  406. <li><p>
    407. 

  407.           By convention, if you return a boolean value indicating success 
    408. 

  408.           then <a class="link" href="glib-Standard-Macros.html#TRUE:CAPS" title="TRUE"><code class="literal">TRUE</code></a> means success and <a class="link" href="glib-Standard-Macros.html#FALSE:CAPS" title="FALSE"><code class="literal">FALSE</code></a> means failure. If <a class="link" href="glib-Standard-Macros.html#FALSE:CAPS" title="FALSE"><code class="literal">FALSE</code></a> is returned,
    409. 

  409.           the error <span class="emphasis"><em>must</em></span> be set to a non-<a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a> value. 
    410. 

  410.         </p></li>
    411. 

  411. <li><p>
    412. 

  412.           A <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a> return value is also frequently used to mean that an error
    413. 

  413.           occurred.  You should make clear in your documentation whether <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a> is
    414. 

  414.           a valid return value in non-error cases; if <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a> is a valid value,
    415. 

  415.           then users must check whether an error was returned to see if the
    416. 

  416.           function succeeded.
    417. 

  417. 	  </p></li>
    418. 

  418. <li><p>
    419. 

  419.           When implementing a function that can report errors, you may want to
    420. 

  420.           add a check at the top of your function that the error return location
    421. 

  421.           is either <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a> or contains a <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a> error
    422. 

  422.           (e.g. <code class="literal">g_return_if_fail (error == NULL || *error ==
    423. 

  423.           NULL);</code>).
    424. 

  424. 	  </p></li>
    425. 

  425. </ul></div>
    426. 

  426. <p>
    427. 

  427. </p>
    428. 

  428. </div>
    429. 

  429. <div class="refsect1" lang="en">
    430. 

  430. <a name="glib-Error-Reporting.details"></a><h2>Details</h2>
    431. 

  431. <div class="refsect2" lang="en">
    432. 

  432. <a name="GError"></a><h3>GError</h3>
    433. 

  433. <pre class="programlisting">typedef struct {
    434. 

  434.   GQuark       domain;
    435. 

  435.   gint         code;
    436. 

  436.   gchar       *message;
    437. 

  437. } GError;
    438. 

  438. </pre>
    439. 

  439. <p>
    440. 

  440. The <span class="structname">GError</span> structure contains 
    441. 

  441. information about an error that has occurred.
    442. 

  442. </p>
    443. 

  443. <div class="variablelist"><table border="0">
    444. 

  444. <col align="left" valign="top">
    445. 

  445. <tbody>
    446. 

  446. <tr>
    447. 

  447. <td><p><span class="term"><a class="link" href="glib-Quarks.html#GQuark" title="GQuark">GQuark</a> <em class="structfield"><code>domain</code></em>;</span></p></td>
    448. 

  448. <td>error domain, e.g. <a class="link" href="glib-File-Utilities.html#G-FILE-ERROR:CAPS" title="G_FILE_ERROR"><span class="type">G_FILE_ERROR</span></a>.
    449. 

  449. </td>
    450. 

  450. </tr>
    451. 

  451. <tr>
    452. 

  452. <td><p><span class="term"><a class="link" href="glib-Basic-Types.html#gint" title="gint">gint</a> <em class="structfield"><code>code</code></em>;</span></p></td>
    453. 

  453. <td>error code, e.g. <a class="link" href="glib-File-Utilities.html#G-FILE-ERROR-NOENT:CAPS"><code class="literal">G_FILE_ERROR_NOENT</code></a>.
    454. 

  454. </td>
    455. 

  455. </tr>
    456. 

  456. <tr>
    457. 

  457. <td><p><span class="term"><a class="link" href="glib-Basic-Types.html#gchar" title="gchar">gchar</a> *<em class="structfield"><code>message</code></em>;</span></p></td>
    458. 

  458. <td>human-readable informative error message.
    459. 

  459. 

  460. </td>
    461. 

  461. </tr>
    462. 

  462. </tbody>
    463. 

  463. </table></div>
    464. 

  464. </div>
    465. 

  465. <hr>
    466. 

  466. <div class="refsect2" lang="en">
    467. 

  467. <a name="g-error-new"></a><h3>g_error_new ()</h3>
    468. 

  468. <pre class="programlisting"><a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a>*             g_error_new                         (<a class="link" href="glib-Quarks.html#GQuark" title="GQuark">GQuark</a> domain,
    469. 

  469.                                                          <a class="link" href="glib-Basic-Types.html#gint" title="gint">gint</a> code,
    470. 

  470.                                                          const <a class="link" href="glib-Basic-Types.html#gchar" title="gchar">gchar</a> *format,
    471. 

  471.                                                          ...);</pre>
    472. 

  472. <p>
    473. 

  473. Creates a new <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a> with the given <em class="parameter"><code>domain</code></em> and <em class="parameter"><code>code</code></em>,
    474. 

  474. and a message formatted with <em class="parameter"><code>format</code></em>.</p>
    475. 

  475. <p>
    476. 

  476. 

  477. </p>
    478. 

  478. <div class="variablelist"><table border="0">
    479. 

  479. <col align="left" valign="top">
    480. 

  480. <tbody>
    481. 

  481. <tr>
    482. 

  482. <td><p><span class="term"><em class="parameter"><code>domain</code></em> :</span></p></td>
    483. 

  483. <td> error domain 
    484. 

  484. </td>
    485. 

  485. </tr>
    486. 

  486. <tr>
    487. 

  487. <td><p><span class="term"><em class="parameter"><code>code</code></em> :</span></p></td>
    488. 

  488. <td> error code
    489. 

  489. </td>
    490. 

  490. </tr>
    491. 

  491. <tr>
    492. 

  492. <td><p><span class="term"><em class="parameter"><code>format</code></em> :</span></p></td>
    493. 

  493. <td> <code class="function">printf()</code>-style format for error message
    494. 

  494. </td>
    495. 

  495. </tr>
    496. 

  496. <tr>
    497. 

  497. <td><p><span class="term"><em class="parameter"><code>...</code></em> :</span></p></td>
    498. 

  498. <td> parameters for message format
    499. 

  499. </td>
    500. 

  500. </tr>
    501. 

  501. <tr>
    502. 

  502. <td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
    503. 

  503. <td> a new <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>
    504. 

  504. </td>
    505. 

  505. </tr>
    506. 

  506. </tbody>
    507. 

  507. </table></div>
    508. 

  508. </div>
    509. 

  509. <hr>
    510. 

  510. <div class="refsect2" lang="en">
    511. 

  511. <a name="g-error-new-literal"></a><h3>g_error_new_literal ()</h3>
    512. 

  512. <pre class="programlisting"><a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a>*             g_error_new_literal                 (<a class="link" href="glib-Quarks.html#GQuark" title="GQuark">GQuark</a> domain,
    513. 

  513.                                                          <a class="link" href="glib-Basic-Types.html#gint" title="gint">gint</a> code,
    514. 

  514.                                                          const <a class="link" href="glib-Basic-Types.html#gchar" title="gchar">gchar</a> *message);</pre>
    515. 

  515. <p>
    516. 

  516. Creates a new <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>; unlike <a class="link" href="glib-Error-Reporting.html#g-error-new" title="g_error_new ()"><code class="function">g_error_new()</code></a>, <em class="parameter"><code>message</code></em> is not
    517. 

  517. a <code class="function">printf()</code>-style format string. Use this 
    518. 

  518. function if <em class="parameter"><code>message</code></em> contains text you don't have control over, 
    519. 

  519. that could include <code class="function">printf()</code> escape sequences.</p>
    520. 

  520. <p>
    521. 

  521. 

  522. </p>
    523. 

  523. <div class="variablelist"><table border="0">
    524. 

  524. <col align="left" valign="top">
    525. 

  525. <tbody>
    526. 

  526. <tr>
    527. 

  527. <td><p><span class="term"><em class="parameter"><code>domain</code></em> :</span></p></td>
    528. 

  528. <td> error domain
    529. 

  529. </td>
    530. 

  530. </tr>
    531. 

  531. <tr>
    532. 

  532. <td><p><span class="term"><em class="parameter"><code>code</code></em> :</span></p></td>
    533. 

  533. <td> error code
    534. 

  534. </td>
    535. 

  535. </tr>
    536. 

  536. <tr>
    537. 

  537. <td><p><span class="term"><em class="parameter"><code>message</code></em> :</span></p></td>
    538. 

  538. <td> error message
    539. 

  539. </td>
    540. 

  540. </tr>
    541. 

  541. <tr>
    542. 

  542. <td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
    543. 

  543. <td> a new <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>
    544. 

  544. </td>
    545. 

  545. </tr>
    546. 

  546. </tbody>
    547. 

  547. </table></div>
    548. 

  548. </div>
    549. 

  549. <hr>
    550. 

  550. <div class="refsect2" lang="en">
    551. 

  551. <a name="g-error-free"></a><h3>g_error_free ()</h3>
    552. 

  552. <pre class="programlisting">void                g_error_free                        (<a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> *error);</pre>
    553. 

  553. <p>
    554. 

  554. Frees a <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a> and associated resources.</p>
    555. 

  555. <p>
    556. 

  556. 

  557. </p>
    558. 

  558. <div class="variablelist"><table border="0">
    559. 

  559. <col align="left" valign="top">
    560. 

  560. <tbody><tr>
    561. 

  561. <td><p><span class="term"><em class="parameter"><code>error</code></em> :</span></p></td>
    562. 

  562. <td> a <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>
    563. 

  563. </td>
    564. 

  564. </tr></tbody>
    565. 

  565. </table></div>
    566. 

  566. </div>
    567. 

  567. <hr>
    568. 

  568. <div class="refsect2" lang="en">
    569. 

  569. <a name="g-error-copy"></a><h3>g_error_copy ()</h3>
    570. 

  570. <pre class="programlisting"><a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a>*             g_error_copy                        (const <a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> *error);</pre>
    571. 

  571. <p>
    572. 

  572. Makes a copy of <em class="parameter"><code>error</code></em>.</p>
    573. 

  573. <p>
    574. 

  574. 

  575. </p>
    576. 

  576. <div class="variablelist"><table border="0">
    577. 

  577. <col align="left" valign="top">
    578. 

  578. <tbody>
    579. 

  579. <tr>
    580. 

  580. <td><p><span class="term"><em class="parameter"><code>error</code></em> :</span></p></td>
    581. 

  581. <td> a <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>
    582. 

  582. </td>
    583. 

  583. </tr>
    584. 

  584. <tr>
    585. 

  585. <td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
    586. 

  586. <td> a new <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>
    587. 

  587. </td>
    588. 

  588. </tr>
    589. 

  589. </tbody>
    590. 

  590. </table></div>
    591. 

  591. </div>
    592. 

  592. <hr>
    593. 

  593. <div class="refsect2" lang="en">
    594. 

  594. <a name="g-error-matches"></a><h3>g_error_matches ()</h3>
    595. 

  595. <pre class="programlisting"><a class="link" href="glib-Basic-Types.html#gboolean" title="gboolean">gboolean</a>            g_error_matches                     (const <a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> *error,
    596. 

  596.                                                          <a class="link" href="glib-Quarks.html#GQuark" title="GQuark">GQuark</a> domain,
    597. 

  597.                                                          <a class="link" href="glib-Basic-Types.html#gint" title="gint">gint</a> code);</pre>
    598. 

  598. <p>
    599. 

  599. Returns <a class="link" href="glib-Standard-Macros.html#TRUE:CAPS" title="TRUE"><code class="literal">TRUE</code></a> if <em class="parameter"><code>error</code></em> matches <em class="parameter"><code>domain</code></em> and <em class="parameter"><code>code</code></em>, <a class="link" href="glib-Standard-Macros.html#FALSE:CAPS" title="FALSE"><code class="literal">FALSE</code></a>
    600. 

  600. otherwise.</p>
    601. 

  601. <p>
    602. 

  602. 

  603. </p>
    604. 

  604. <div class="variablelist"><table border="0">
    605. 

  605. <col align="left" valign="top">
    606. 

  606. <tbody>
    607. 

  607. <tr>
    608. 

  608. <td><p><span class="term"><em class="parameter"><code>error</code></em> :</span></p></td>
    609. 

  609. <td> a <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>
    610. 

  610. </td>
    611. 

  611. </tr>
    612. 

  612. <tr>
    613. 

  613. <td><p><span class="term"><em class="parameter"><code>domain</code></em> :</span></p></td>
    614. 

  614. <td> an error domain
    615. 

  615. </td>
    616. 

  616. </tr>
    617. 

  617. <tr>
    618. 

  618. <td><p><span class="term"><em class="parameter"><code>code</code></em> :</span></p></td>
    619. 

  619. <td> an error code
    620. 

  620. </td>
    621. 

  621. </tr>
    622. 

  622. <tr>
    623. 

  623. <td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
    624. 

  624. <td> whether <em class="parameter"><code>error</code></em> has <em class="parameter"><code>domain</code></em> and <em class="parameter"><code>code</code></em>
    625. 

  625. </td>
    626. 

  626. </tr>
    627. 

  627. </tbody>
    628. 

  628. </table></div>
    629. 

  629. </div>
    630. 

  630. <hr>
    631. 

  631. <div class="refsect2" lang="en">
    632. 

  632. <a name="g-set-error"></a><h3>g_set_error ()</h3>
    633. 

  633. <pre class="programlisting">void                g_set_error                         (<a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> **err,
    634. 

  634.                                                          <a class="link" href="glib-Quarks.html#GQuark" title="GQuark">GQuark</a> domain,
    635. 

  635.                                                          <a class="link" href="glib-Basic-Types.html#gint" title="gint">gint</a> code,
    636. 

  636.                                                          const <a class="link" href="glib-Basic-Types.html#gchar" title="gchar">gchar</a> *format,
    637. 

  637.                                                          ...);</pre>
    638. 

  638. <p>
    639. 

  639. Does nothing if <em class="parameter"><code>err</code></em> is <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a>; if <em class="parameter"><code>err</code></em> is non-<a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a>, then *<em class="parameter"><code>err</code></em> must
    640. 

  640. be <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a>. A new <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a> is created and assigned to *<em class="parameter"><code>err</code></em>.</p>
    641. 

  641. <p>
    642. 

  642. 

  643. </p>
    644. 

  644. <div class="variablelist"><table border="0">
    645. 

  645. <col align="left" valign="top">
    646. 

  646. <tbody>
    647. 

  647. <tr>
    648. 

  648. <td><p><span class="term"><em class="parameter"><code>err</code></em> :</span></p></td>
    649. 

  649. <td> a return location for a <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>, or <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a>
    650. 

  650. </td>
    651. 

  651. </tr>
    652. 

  652. <tr>
    653. 

  653. <td><p><span class="term"><em class="parameter"><code>domain</code></em> :</span></p></td>
    654. 

  654. <td> error domain
    655. 

  655. </td>
    656. 

  656. </tr>
    657. 

  657. <tr>
    658. 

  658. <td><p><span class="term"><em class="parameter"><code>code</code></em> :</span></p></td>
    659. 

  659. <td> error code 
    660. 

  660. </td>
    661. 

  661. </tr>
    662. 

  662. <tr>
    663. 

  663. <td><p><span class="term"><em class="parameter"><code>format</code></em> :</span></p></td>
    664. 

  664. <td> <code class="function">printf()</code>-style format
    665. 

  665. </td>
    666. 

  666. </tr>
    667. 

  667. <tr>
    668. 

  668. <td><p><span class="term"><em class="parameter"><code>...</code></em> :</span></p></td>
    669. 

  669. <td> args for <em class="parameter"><code>format</code></em> 
    670. 

  670. </td>
    671. 

  671. </tr>
    672. 

  672. </tbody>
    673. 

  673. </table></div>
    674. 

  674. </div>
    675. 

  675. <hr>
    676. 

  676. <div class="refsect2" lang="en">
    677. 

  677. <a name="g-propagate-error"></a><h3>g_propagate_error ()</h3>
    678. 

  678. <pre class="programlisting">void                g_propagate_error                   (<a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> **dest,
    679. 

  679.                                                          <a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> *src);</pre>
    680. 

  680. <p>
    681. 

  681. If <em class="parameter"><code>dest</code></em> is <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a>, free <em class="parameter"><code>src</code></em>; otherwise, moves <em class="parameter"><code>src</code></em> into *<em class="parameter"><code>dest</code></em>.
    682. 

  682. The error variable <em class="parameter"><code>dest</code></em> points to must be <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a>.</p>
    683. 

  683. <p>
    684. 

  684. 

  685. </p>
    686. 

  686. <div class="variablelist"><table border="0">
    687. 

  687. <col align="left" valign="top">
    688. 

  688. <tbody>
    689. 

  689. <tr>
    690. 

  690. <td><p><span class="term"><em class="parameter"><code>dest</code></em> :</span></p></td>
    691. 

  691. <td> error return location
    692. 

  692. </td>
    693. 

  693. </tr>
    694. 

  694. <tr>
    695. 

  695. <td><p><span class="term"><em class="parameter"><code>src</code></em> :</span></p></td>
    696. 

  696. <td> error to move into the return location
    697. 

  697. </td>
    698. 

  698. </tr>
    699. 

  699. </tbody>
    700. 

  700. </table></div>
    701. 

  701. </div>
    702. 

  702. <hr>
    703. 

  703. <div class="refsect2" lang="en">
    704. 

  704. <a name="g-clear-error"></a><h3>g_clear_error ()</h3>
    705. 

  705. <pre class="programlisting">void                g_clear_error                       (<a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> **err);</pre>
    706. 

  706. <p>
    707. 

  707. If <em class="parameter"><code>err</code></em> is <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a>, does nothing. If <em class="parameter"><code>err</code></em> is non-<a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a>,
    708. 

  708. calls <a class="link" href="glib-Error-Reporting.html#g-error-free" title="g_error_free ()"><code class="function">g_error_free()</code></a> on *<em class="parameter"><code>err</code></em> and sets *<em class="parameter"><code>err</code></em> to <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a>.</p>
    709. 

  709. <p>
    710. 

  710. 

  711. </p>
    712. 

  712. <div class="variablelist"><table border="0">
    713. 

  713. <col align="left" valign="top">
    714. 

  714. <tbody><tr>
    715. 

  715. <td><p><span class="term"><em class="parameter"><code>err</code></em> :</span></p></td>
    716. 

  716. <td> a <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a> return location
    717. 

  717. </td>
    718. 

  718. </tr></tbody>
    719. 

  719. </table></div>
    720. 

  720. </div>
    721. 

  721. <hr>
    722. 

  722. <div class="refsect2" lang="en">
    723. 

  723. <a name="g-prefix-error"></a><h3>g_prefix_error ()</h3>
    724. 

  724. <pre class="programlisting">void                g_prefix_error                      (<a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> **err,
    725. 

  725.                                                          const <a class="link" href="glib-Basic-Types.html#gchar" title="gchar">gchar</a> *format,
    726. 

  726.                                                          ...);</pre>
    727. 

  727. <p>
    728. 

  728. Formats a string according to <em class="parameter"><code>format</code></em> and
    729. 

  729. prefix it to an existing error message.  If
    730. 

  730. <em class="parameter"><code>err</code></em> is <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a> (ie: no error variable) then do
    731. 

  731. nothing.
    732. 

  732. </p>
    733. 

  733. <p>
    734. 

  734. If *<em class="parameter"><code>err</code></em> is <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a> (ie: an error variable is
    735. 

  735. present but there is no error condition) then
    736. 

  736. also do nothing.  Whether or not it makes
    737. 

  737. sense to take advantage of this feature is up
    738. 

  738. to you.</p>
    739. 

  739. <p>
    740. 

  740. 

  741. </p>
    742. 

  742. <div class="variablelist"><table border="0">
    743. 

  743. <col align="left" valign="top">
    744. 

  744. <tbody>
    745. 

  745. <tr>
    746. 

  746. <td><p><span class="term"><em class="parameter"><code>err</code></em> :</span></p></td>
    747. 

  747. <td> a return location for a <a class="link" href="glib-Error-Reporting.html#GError" title="GError"><span class="type">GError</span></a>, or <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a>
    748. 

  748. </td>
    749. 

  749. </tr>
    750. 

  750. <tr>
    751. 

  751. <td><p><span class="term"><em class="parameter"><code>format</code></em> :</span></p></td>
    752. 

  752. <td> <code class="function">printf()</code>-style format string
    753. 

  753. </td>
    754. 

  754. </tr>
    755. 

  755. <tr>
    756. 

  756. <td><p><span class="term"><em class="parameter"><code>...</code></em> :</span></p></td>
    757. 

  757. <td> arguments to <em class="parameter"><code>format</code></em>
    758. 

  758. </td>
    759. 

  759. </tr>
    760. 

  760. </tbody>
    761. 

  761. </table></div>
    762. 

  762. <p class="since">Since  2.16
    763. 

  763. </p>
    764. 

  764. </div>
    765. 

  765. <hr>
    766. 

  766. <div class="refsect2" lang="en">
    767. 

  767. <a name="g-propagate-prefixed-error"></a><h3>g_propagate_prefixed_error ()</h3>
    768. 

  768. <pre class="programlisting">void                g_propagate_prefixed_error          (<a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> **dest,
    769. 

  769.                                                          <a class="link" href="glib-Error-Reporting.html#GError" title="GError">GError</a> *src,
    770. 

  770.                                                          const <a class="link" href="glib-Basic-Types.html#gchar" title="gchar">gchar</a> *format,
    771. 

  771.                                                          ...);</pre>
    772. 

  772. <p>
    773. 

  773. If <em class="parameter"><code>dest</code></em> is <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a>, free <em class="parameter"><code>src</code></em>; otherwise,
    774. 

  774. moves <em class="parameter"><code>src</code></em> into *<em class="parameter"><code>dest</code></em>. *<em class="parameter"><code>dest</code></em> must be <a class="link" href="glib-Standard-Macros.html#NULL:CAPS" title="NULL"><code class="literal">NULL</code></a>.
    775. 

  775. After the move, add a prefix as with 
    776. 

  776. <a class="link" href="glib-Error-Reporting.html#g-prefix-error" title="g_prefix_error ()"><code class="function">g_prefix_error()</code></a>.</p>
    777. 

  777. <p>
    778. 

  778. 

  779. </p>
    780. 

  780. <div class="variablelist"><table border="0">
    781. 

  781. <col align="left" valign="top">
    782. 

  782. <tbody>
    783. 

  783. <tr>
    784. 

  784. <td><p><span class="term"><em class="parameter"><code>dest</code></em> :</span></p></td>
    785. 

  785. <td> error return location
    786. 

  786. </td>
    787. 

  787. </tr>
    788. 

  788. <tr>
    789. 

  789. <td><p><span class="term"><em class="parameter"><code>src</code></em> :</span></p></td>
    790. 

  790. <td> error to move into the return location
    791. 

  791. </td>
    792. 

  792. </tr>
    793. 

  793. <tr>
    794. 

  794. <td><p><span class="term"><em class="parameter"><code>format</code></em> :</span></p></td>
    795. 

  795. <td> <code class="function">printf()</code>-style format string
    796. 

  796. </td>
    797. 

  797. </tr>
    798. 

  798. <tr>
    799. 

  799. <td><p><span class="term"><em class="parameter"><code>...</code></em> :</span></p></td>
    800. 

  800. <td> arguments to <em class="parameter"><code>format</code></em>
    801. 

  801. </td>
    802. 

  802. </tr>
    803. 

  803. </tbody>
    804. 

  804. </table></div>
    805. 

  805. <p class="since">Since  2.16
    806. 

  806. </p>
    807. 

  807. </div>
    808. 

  808. </div>
    809. 

  809. </div>
    810. 

  810. <div class="footer">
    811. 

  811. <hr>
    812. 

  812.           Generated by GTK-Doc V1.10</div>
    813. 

  813. </body>
    814. 

  814. </html>
    815.