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  6. <title>Magick++ API: Exceptions </title>
  7. <link rel="stylesheet" href="magick.css" type="text/css" />
  8. </head>
  9. <body>
  10. <div class="doc-section">
  11. <h1 align="center">Magick::Exception Classes</h1>
  12. <p><i>Exception</i> represents the base class of objects thrown when
  13. Magick++reports an error. Magick++ throws C++ exceptions synchronous
  14. with the operation where the error occurred. This allows errors to be
  15. trapped within the enclosing code (perhaps the code to process a
  16. single image) while allowing the code to be written with a simple
  17. coding style.</p>
  18. <p>A try/catch block should be placed around any sequence of
  19. operations which can be considered an important body of work. For
  20. example, if your program processes lists of images and some of these
  21. images may be defective, by placing the try/catch block around the
  22. entire sequence of code that processes one image (including
  23. instantiating the image object), you can minimize the overhead of
  24. error checking while ensuring that all objects created to deal with
  25. that object are safely destroyed (C++ exceptions unroll the stack
  26. until the enclosing try block, destroying any created objects).
  27. </p>
  28. <p>The pseudo code for the main loop of your program may look like:
  29. </p>
  30. <div class="viewport">
  31. using namespace std;
  32. for infile in list
  33. {
  34. try {
  35. // Construct an image instance first so that we don't have to worry
  36. // about object construction failure due to a minor warning exception
  37. // being thrown.
  38. Magick::Image image;
  39. try {
  40. // Try reading image file
  41. image.read(infile);
  42. }
  43. catch( Magick::WarningCoder &amp;warning )
  44. {
  45. // Process coder warning while loading file (e.g. TIFF warning)
  46. // Maybe the user will be interested in these warnings (or not).
  47. // If a warning is produced while loading an image, the image
  48. // can normally still be used (but not if the warning was about
  49. // something important!)
  50. cerr &lt;&lt; "Coder Warning: " &lt;&lt; warning.what() &lt;&lt; endl;
  51. }
  52. catch( Magick::Warning &amp;warning )
  53. {
  54. // Handle any other Magick++ warning.
  55. cerr &lt;&lt; "Warning: " &lt;&lt; warning.what() &lt;&lt; endl;
  56. }
  57. catch( Magick::ErrorFileOpen &amp;error )
  58. {
  59. // Process Magick++ file open error
  60. cerr &lt;&lt; "Error: " &lt;&lt; error.what() &lt;&lt; endl;
  61. continue; // Try next image.
  62. }
  63. try {
  64. image.rotate(90);
  65. image.write("outfile");
  66. }
  67. catch ( MagickExeption &amp; error)
  68. {
  69. // Handle problem while rotating or writing outfile.
  70. cerr &lt;&lt; "Caught Magick++ exception: " &lt;&lt; error.what() &lt;&lt; endl;
  71. }
  72. }
  73. catch( std::exception &amp; error )
  74. {
  75. // Process any other exceptions derived from standard C++ exception
  76. cerr &lt;&lt; "Caught C++ STD exception: " &lt;&lt; error.what() &lt;&lt; endl;
  77. }
  78. catch( ... )
  79. {
  80. // Process *any* exception (last-ditch effort). There is not a lot
  81. // you can do here other to retry the operation that failed, or exit
  82. }
  83. }
  84. </div>
  85. <p>The desired location and number of try/catch blocks in your program
  86. depends how sophisticated its error handling must be. Very simple
  87. programs may use just one try/catch block.</p>
  88. <p>The <i>Exception</i> class is derived from the C++ standard
  89. exception class. This means that it contains a C++ string containing
  90. additional information about the error (e.g to display to the user).
  91. Obtain access to this string via the what() method.&#160; For
  92. example:
  93. </p>
  94. <pre class="code">
  95. catch( Exception &amp; error_ )
  96. {
  97. cout &lt;&lt; "Caught exception: " &lt;&lt; error_.what() &lt;&lt; endl;
  98. }
  99. </pre>
  100. <p>The classes <i>Warning</i> and <i>Error</i> derive from the
  101. <i>Exception</i> class. Exceptions derived from <i>Warning</i> are
  102. thrown to represent non-fatal errors which may effect the
  103. completeness or quality of the result (e.g. one image provided as an
  104. argument to montage is defective). In most cases, a <i>Warning</i>
  105. exception may be ignored by catching it immediately, processing it
  106. (e.g. printing a diagnostic) and continuing on. Exceptions derived
  107. from <i>Error</i> are thrown to represent fatal errors that can not
  108. produce a valid result (e.g. attempting to read a file which does not
  109. exist).
  110. </p>
  111. <p style="margin-bottom: 0in">The specific derived exception classes
  112. are shown in the following tables:
  113. </p>
  114. <p align="center" style="margin-bottom: 0in"><b>Warning Sub-Classes</b></p>
  115. <ul><table width="100%" border="1" cellpadding="2" cellspacing="3">
  116. <col width="70*" />
  117. <col width="186*" />
  118. <tr>
  119. <td width="27%">
  120. <p align="center"><font size="2"><b>Warning</b></font></p>
  121. </td>
  122. <td width="73%">
  123. <p align="center"><font size="2"><b>Warning Description</b></font></p>
  124. </td>
  125. </tr>
  126. <tr>
  127. <td width="27%">
  128. <p align="center"><font size="2">WarningUndefined</font></p>
  129. </td>
  130. <td width="73%">
  131. <p><font size="2">Unspecified warning type.</font></p>
  132. </td>
  133. </tr>
  134. <tr>
  135. <td width="27%">
  136. <p align="center"><font size="2">WarningBlob</font></p>
  137. </td>
  138. <td width="73%">
  139. <p style="font-weight: medium; text-decoration: none"><font size="2">NOT
  140. CURRENTLY USED</font></p>
  141. </td>
  142. </tr>
  143. <tr>
  144. <td width="27%">
  145. <p align="center"><font size="2">WarningCache</font></p>
  146. </td>
  147. <td width="73%">
  148. <p style="font-weight: medium; text-decoration: none"><font size="2">NOT
  149. CURRENTLY USED</font></p>
  150. </td>
  151. </tr>
  152. <tr>
  153. <td width="27%">
  154. <p align="center"><font size="2">WarningCoder</font></p>
  155. </td>
  156. <td width="73%">
  157. <p><font size="2">Warnings issued by some coders.</font></p>
  158. </td>
  159. </tr>
  160. <tr>
  161. <td width="27%">
  162. <p align="center"><font size="2">WarningConfigure</font></p>
  163. </td>
  164. <td width="73%">
  165. <p style="font-weight: medium; text-decoration: none"><font size="2">NOT
  166. CURRENTLY USED</font></p>
  167. </td>
  168. </tr>
  169. <tr>
  170. <td width="27%">
  171. <p align="center"><font size="2">WarningCorruptImage</font></p>
  172. </td>
  173. <td width="73%">
  174. <p><font size="2">Warning issued when an image is determined to be
  175. corrupt.</font></p>
  176. </td>
  177. </tr>
  178. <tr>
  179. <td width="27%">
  180. <p align="center"><font size="2">WarningDelegate</font></p>
  181. </td>
  182. <td width="73%">
  183. <p><font size="2">Warnings reported by the delegate (interface to
  184. external programs) subsystem.</font></p>
  185. </td>
  186. </tr>
  187. <tr>
  188. <td width="27%">
  189. <p align="center"><font size="2">WarningDraw</font></p>
  190. </td>
  191. <td width="73%">
  192. <p><font size="2">Warnings reported by the rendering subsystem.</font></p>
  193. </td>
  194. </tr>
  195. <tr>
  196. <td width="27%">
  197. <p align="center"><font size="2">WarningFileOpen</font></p>
  198. </td>
  199. <td width="73%">
  200. <p><font size="2">Warning reported when The image file could not be
  201. opened (permission problem, wrong file type, or does not exist).</font></p>
  202. </td>
  203. </tr>
  204. <tr>
  205. <td width="27%">
  206. <p align="center"><font size="2">WarningImage</font></p>
  207. </td>
  208. <td width="73%">
  209. <p style="font-weight: medium"><font size="2">NOT CURRENTLY USED</font></p>
  210. </td>
  211. </tr>
  212. <tr>
  213. <td width="27%">
  214. <p align="center"><font size="2">WarningMissingDelegate</font></p>
  215. </td>
  216. <td width="73%">
  217. <p style="font-weight: medium"><font size="2">NOT CURRENTLY USED</font></p>
  218. </td>
  219. </tr>
  220. <tr>
  221. <td width="27%">
  222. <p align="center"><font size="2">WarningModule</font></p>
  223. </td>
  224. <td width="73%">
  225. <p style="font-weight: medium"><font size="2">NOT CURRENTLY USED</font></p>
  226. </td>
  227. </tr>
  228. <tr>
  229. <td width="27%">
  230. <p align="center"><font size="2">WarningMonitor</font></p>
  231. </td>
  232. <td width="73%">
  233. <p style="font-weight: medium"><font size="2">NOT CURRENTLY USED</font></p>
  234. </td>
  235. </tr>
  236. <tr>
  237. <td width="27%">
  238. <p align="center"><font size="2">WarningOption</font></p>
  239. </td>
  240. <td width="73%">
  241. <p><font size="2">Warning reported when an option is malformed or
  242. out of range.</font></p>
  243. </td>
  244. </tr>
  245. <tr>
  246. <td width="27%">
  247. <p align="center"><font size="2">WarningRegistry</font></p>
  248. </td>
  249. <td width="73%">
  250. <p style="font-weight: medium"><font size="2">NOT CURRENTLY USED</font></p>
  251. </td>
  252. </tr>
  253. <tr>
  254. <td width="27%">
  255. <p align="center"><font size="2">WarningResourceLimit</font></p>
  256. </td>
  257. <td width="73%">
  258. <p><font size="2">Warning reported when a program resource is
  259. exhausted (e.g. not enough memory).</font></p>
  260. </td>
  261. </tr>
  262. <tr>
  263. <td width="27%">
  264. <p align="center"><font size="2">WarningStream</font></p>
  265. </td>
  266. <td width="73%">
  267. <p style="font-weight: medium"><font size="2">NOT CURRENTLY USED</font></p>
  268. </td>
  269. </tr>
  270. <tr>
  271. <td width="27%">
  272. <p align="center"><font size="2">WarningType</font></p>
  273. </td>
  274. <td width="73%">
  275. <p style="font-weight: medium"><font size="2">NOT CURRENTLY USED</font></p>
  276. </td>
  277. </tr>
  278. <tr>
  279. <td width="27%">
  280. <p align="center"><font size="2">WarningXServer</font></p>
  281. </td>
  282. <td width="73%">
  283. <p><font size="2">Warnings reported by the X11 subsystem.</font></p>
  284. </td>
  285. </tr>
  286. </table></ul>
  287. <p style="margin-bottom: 0in"><br />
  288. </p>
  289. <p align="center" style="margin-bottom: 0in"><b>Error Sub-Classes</b></p>
  290. <ul><table width="100%" border="1" cellpadding="2" cellspacing="3">
  291. <col width="71*" />
  292. <col width="185*" />
  293. <tr>
  294. <td width="28%">
  295. <p align="center"><font size="2"><b>Error</b></font></p>
  296. </td>
  297. <td width="72%">
  298. <p align="center"><font size="2"><b>Error Description</b></font></p>
  299. </td>
  300. </tr>
  301. <tr>
  302. <td width="28%">
  303. <p align="center"><font size="2">ErrorUndefined</font></p>
  304. </td>
  305. <td width="72%">
  306. <p><font size="2">Unspecified error type.</font></p>
  307. </td>
  308. </tr>
  309. <tr>
  310. <td width="28%">
  311. <p align="center"><font size="2">ErrorBlob</font></p>
  312. </td>
  313. <td width="72%">
  314. <p><font size="2">Error reported by BLOB I/O subsystem.</font></p>
  315. </td>
  316. </tr>
  317. <tr>
  318. <td width="28%">
  319. <p align="center"><font size="2">ErrorCache</font></p>
  320. </td>
  321. <td width="72%">
  322. <p><font size="2">Error reported by the pixel cache subsystem.</font></p>
  323. </td>
  324. </tr>
  325. <tr>
  326. <td width="28%">
  327. <p align="center"><font size="2">ErrorCoder</font></p>
  328. </td>
  329. <td width="72%">
  330. <p><font size="2">Error reported by coders (image format support).</font></p>
  331. </td>
  332. </tr>
  333. <tr>
  334. <td width="28%">
  335. <p align="center"><font size="2">ErrorConfigure</font></p>
  336. </td>
  337. <td width="72%">
  338. <p><font size="2">Errors reported while loading configuration files.</font></p>
  339. </td>
  340. </tr>
  341. <tr>
  342. <td width="28%">
  343. <p align="center"><font size="2">ErrorCorruptImage</font></p>
  344. </td>
  345. <td width="72%">
  346. <p><font size="2">Error reported when the image file is corrupt.</font></p>
  347. </td>
  348. </tr>
  349. <tr>
  350. <td width="28%">
  351. <p align="center"><font size="2">ErrorDelegate</font></p>
  352. </td>
  353. <td width="72%">
  354. <p><font size="2">Errors reported by the delegate (interface to
  355. external programs) subsystem.</font></p>
  356. </td>
  357. </tr>
  358. <tr>
  359. <td width="28%">
  360. <p align="center"><font size="2">ErrorDraw</font></p>
  361. </td>
  362. <td width="72%">
  363. <p><font size="2">Error reported while drawing on image.</font></p>
  364. </td>
  365. </tr>
  366. <tr>
  367. <td width="28%">
  368. <p align="center"><font size="2">ErrorFileOpen</font></p>
  369. </td>
  370. <td width="72%">
  371. <p><font size="2">Error reported when the image file can not be
  372. opened.</font></p>
  373. </td>
  374. </tr>
  375. <tr>
  376. <td width="28%">
  377. <p align="center"><font size="2">ErrorImage</font></p>
  378. </td>
  379. <td width="72%">
  380. <p><font size="2">Errors reported while drawing.</font></p>
  381. </td>
  382. </tr>
  383. <tr>
  384. <td width="28%">
  385. <p align="center"><font size="2">ErrorMissingDelegate</font></p>
  386. </td>
  387. <td width="72%">
  388. <p><font size="2">Error reported when an add-on library or program
  389. is necessary in order to support the requested operation.</font></p>
  390. </td>
  391. </tr>
  392. <tr>
  393. <td width="28%">
  394. <p align="center"><font size="2">ErrorModule</font></p>
  395. </td>
  396. <td width="72%">
  397. <p><font size="2">Errors reported by the module loader subsystem.</font></p>
  398. </td>
  399. </tr>
  400. <tr>
  401. <td width="28%">
  402. <p align="center"><font size="2">ErrorMonitor</font></p>
  403. </td>
  404. <td width="72%">
  405. <p style="font-weight: medium"><font size="2">NOT CURRENTLY USED</font></p>
  406. </td>
  407. </tr>
  408. <tr>
  409. <td width="28%">
  410. <p align="center"><font size="2">ErrorOption</font></p>
  411. </td>
  412. <td width="72%">
  413. <p><font size="2">Error reported when an option is malformed or out
  414. of range.</font></p>
  415. </td>
  416. </tr>
  417. <tr>
  418. <td width="28%">
  419. <p align="center"><font size="2">ErrorRegistry</font></p>
  420. </td>
  421. <td width="72%">
  422. <p><font size="2">Errors reported by the image/BLOB registry
  423. subsystem.</font></p>
  424. </td>
  425. </tr>
  426. <tr>
  427. <td width="28%">
  428. <p align="center"><font size="2">ErrorResourceLimit</font></p>
  429. </td>
  430. <td width="72%">
  431. <p><font size="2">Error reported when a program resource is
  432. exhausted (e.g. not enough memory).</font></p>
  433. </td>
  434. </tr>
  435. <tr>
  436. <td width="28%">
  437. <p align="center"><font size="2">ErrorStream</font></p>
  438. </td>
  439. <td width="72%">
  440. <p><font size="2">Errors reported by the pixel stream subsystem.</font></p>
  441. </td>
  442. </tr>
  443. <tr>
  444. <td width="28%">
  445. <p align="center"><font size="2">ErrorType</font></p>
  446. </td>
  447. <td width="72%">
  448. <p><font size="2">Errors reported by the type (font) rendering
  449. subsystem.</font></p>
  450. </td>
  451. </tr>
  452. <tr>
  453. <td width="28%">
  454. <p align="center"><font size="2">ErrorXServer</font></p>
  455. </td>
  456. <td width="72%">
  457. <p><font size="2">Errors reported by the X11 subsystem.</font></p>
  458. </td>
  459. </tr>
  460. </table></ul>
  461. <p><br /><br />
  462. </p>
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