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<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Magick++ API: Exceptions </title>
<link rel="stylesheet" href="magick.css" type="text/css" />
</head>
<body>
<div class="doc-section">
<h1 align="center">Magick::Exception Classes</h1>
<p><i>Exception</i> represents the base class of objects thrown when
Magick++reports an error. Magick++ throws C++ exceptions synchronous
with the operation where the error occurred. This allows errors to be
trapped within the enclosing code (perhaps the code to process a
single image) while allowing the code to be written with a simple
coding style.</p>
<p>A try/catch block should be placed around any sequence of
operations which can be considered an important body of work. For
example, if your program processes lists of images and some of these
images may be defective, by placing the try/catch block around the
entire sequence of code that processes one image (including
instantiating the image object), you can minimize the overhead of
error checking while ensuring that all objects created to deal with
that object are safely destroyed (C++ exceptions unroll the stack
until the enclosing try block, destroying any created objects).
</p>
<p>The pseudo code for the main loop of your program may look like:
</p>
<div class="viewport">
using namespace std;
for infile in list
{
try {
// Construct an image instance first so that we don't have to worry
// about object construction failure due to a minor warning exception
// being thrown.
Magick::Image image;
try {
// Try reading image file
image.read(infile);
}
catch( Magick::WarningCoder &amp;warning )
{
// Process coder warning while loading file (e.g. TIFF warning)
// Maybe the user will be interested in these warnings (or not).
// If a warning is produced while loading an image, the image
// can normally still be used (but not if the warning was about
// something important!)
cerr &lt;&lt; "Coder Warning: " &lt;&lt; warning.what() &lt;&lt; endl;
}
catch( Magick::Warning &amp;warning )
{
// Handle any other Magick++ warning.
cerr &lt;&lt; "Warning: " &lt;&lt; warning.what() &lt;&lt; endl;
}
catch( Magick::ErrorFileOpen &amp;error )
{
// Process Magick++ file open error
cerr &lt;&lt; "Error: " &lt;&lt; error.what() &lt;&lt; endl;
continue; // Try next image.
}
try {
image.rotate(90);
image.write("outfile");
}
catch ( MagickExeption &amp; error)
{
// Handle problem while rotating or writing outfile.
cerr &lt;&lt; "Caught Magick++ exception: " &lt;&lt; error.what() &lt;&lt; endl;
}
}
catch( std::exception &amp; error )
{
// Process any other exceptions derived from standard C++ exception
cerr &lt;&lt; "Caught C++ STD exception: " &lt;&lt; error.what() &lt;&lt; endl;
}
catch( ... )
{
// Process *any* exception (last-ditch effort). There is not a lot
// you can do here other to retry the operation that failed, or exit
}
}
</div>
<p>The desired location and number of try/catch blocks in your program
depends how sophisticated its error handling must be. Very simple
programs may use just one try/catch block.</p>
<p>The <i>Exception</i> class is derived from the C++ standard
exception class. This means that it contains a C++ string containing
additional information about the error (e.g to display to the user).
Obtain access to this string via the what() method.&#160; For
example:
</p>
<pre class="code">
catch( Exception &amp; error_ )
{
cout &lt;&lt; "Caught exception: " &lt;&lt; error_.what() &lt;&lt; endl;
}
</pre>
<p>The classes <i>Warning</i> and <i>Error</i> derive from the
<i>Exception</i> class. Exceptions derived from <i>Warning</i> are
thrown to represent non-fatal errors which may effect the
completeness or quality of the result (e.g. one image provided as an
argument to montage is defective). In most cases, a <i>Warning</i>
exception may be ignored by catching it immediately, processing it
(e.g. printing a diagnostic) and continuing on. Exceptions derived
from <i>Error</i> are thrown to represent fatal errors that can not
produce a valid result (e.g. attempting to read a file which does not
exist).
</p>
<p style="margin-bottom: 0in">The specific derived exception classes
are shown in the following tables:
</p>
<p align="center" style="margin-bottom: 0in"><b>Warning Sub-Classes</b></p>
<ul><table width="100%" border="1" cellpadding="2" cellspacing="3">
<col width="70*" />
<col width="186*" />
<tr>
<td width="27%">
<p align="center"><font size="2"><b>Warning</b></font></p>
</td>
<td width="73%">
<p align="center"><font size="2"><b>Warning Description</b></font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningUndefined</font></p>
</td>
<td width="73%">
<p><font size="2">Unspecified warning type.</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningBlob</font></p>
</td>
<td width="73%">
<p style="font-weight: medium; text-decoration: none"><font size="2">NOT
CURRENTLY USED</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningCache</font></p>
</td>
<td width="73%">
<p style="font-weight: medium; text-decoration: none"><font size="2">NOT
CURRENTLY USED</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningCoder</font></p>
</td>
<td width="73%">
<p><font size="2">Warnings issued by some coders.</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningConfigure</font></p>
</td>
<td width="73%">
<p style="font-weight: medium; text-decoration: none"><font size="2">NOT
CURRENTLY USED</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningCorruptImage</font></p>
</td>
<td width="73%">
<p><font size="2">Warning issued when an image is determined to be
corrupt.</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningDelegate</font></p>
</td>
<td width="73%">
<p><font size="2">Warnings reported by the delegate (interface to
external programs) subsystem.</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningDraw</font></p>
</td>
<td width="73%">
<p><font size="2">Warnings reported by the rendering subsystem.</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningFileOpen</font></p>
</td>
<td width="73%">
<p><font size="2">Warning reported when The image file could not be
opened (permission problem, wrong file type, or does not exist).</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningImage</font></p>
</td>
<td width="73%">
<p style="font-weight: medium"><font size="2">NOT CURRENTLY USED</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningMissingDelegate</font></p>
</td>
<td width="73%">
<p style="font-weight: medium"><font size="2">NOT CURRENTLY USED</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningModule</font></p>
</td>
<td width="73%">
<p style="font-weight: medium"><font size="2">NOT CURRENTLY USED</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningMonitor</font></p>
</td>
<td width="73%">
<p style="font-weight: medium"><font size="2">NOT CURRENTLY USED</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningOption</font></p>
</td>
<td width="73%">
<p><font size="2">Warning reported when an option is malformed or
out of range.</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningRegistry</font></p>
</td>
<td width="73%">
<p style="font-weight: medium"><font size="2">NOT CURRENTLY USED</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningResourceLimit</font></p>
</td>
<td width="73%">
<p><font size="2">Warning reported when a program resource is
exhausted (e.g. not enough memory).</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningStream</font></p>
</td>
<td width="73%">
<p style="font-weight: medium"><font size="2">NOT CURRENTLY USED</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningType</font></p>
</td>
<td width="73%">
<p style="font-weight: medium"><font size="2">NOT CURRENTLY USED</font></p>
</td>
</tr>
<tr>
<td width="27%">
<p align="center"><font size="2">WarningXServer</font></p>
</td>
<td width="73%">
<p><font size="2">Warnings reported by the X11 subsystem.</font></p>
</td>
</tr>
</table></ul>
<p style="margin-bottom: 0in"><br />
</p>
<p align="center" style="margin-bottom: 0in"><b>Error Sub-Classes</b></p>
<ul><table width="100%" border="1" cellpadding="2" cellspacing="3">
<col width="71*" />
<col width="185*" />
<tr>
<td width="28%">
<p align="center"><font size="2"><b>Error</b></font></p>
</td>
<td width="72%">
<p align="center"><font size="2"><b>Error Description</b></font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorUndefined</font></p>
</td>
<td width="72%">
<p><font size="2">Unspecified error type.</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorBlob</font></p>
</td>
<td width="72%">
<p><font size="2">Error reported by BLOB I/O subsystem.</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorCache</font></p>
</td>
<td width="72%">
<p><font size="2">Error reported by the pixel cache subsystem.</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorCoder</font></p>
</td>
<td width="72%">
<p><font size="2">Error reported by coders (image format support).</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorConfigure</font></p>
</td>
<td width="72%">
<p><font size="2">Errors reported while loading configuration files.</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorCorruptImage</font></p>
</td>
<td width="72%">
<p><font size="2">Error reported when the image file is corrupt.</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorDelegate</font></p>
</td>
<td width="72%">
<p><font size="2">Errors reported by the delegate (interface to
external programs) subsystem.</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorDraw</font></p>
</td>
<td width="72%">
<p><font size="2">Error reported while drawing on image.</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorFileOpen</font></p>
</td>
<td width="72%">
<p><font size="2">Error reported when the image file can not be
opened.</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorImage</font></p>
</td>
<td width="72%">
<p><font size="2">Errors reported while drawing.</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorMissingDelegate</font></p>
</td>
<td width="72%">
<p><font size="2">Error reported when an add-on library or program
is necessary in order to support the requested operation.</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorModule</font></p>
</td>
<td width="72%">
<p><font size="2">Errors reported by the module loader subsystem.</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorMonitor</font></p>
</td>
<td width="72%">
<p style="font-weight: medium"><font size="2">NOT CURRENTLY USED</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorOption</font></p>
</td>
<td width="72%">
<p><font size="2">Error reported when an option is malformed or out
of range.</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorRegistry</font></p>
</td>
<td width="72%">
<p><font size="2">Errors reported by the image/BLOB registry
subsystem.</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorResourceLimit</font></p>
</td>
<td width="72%">
<p><font size="2">Error reported when a program resource is
exhausted (e.g. not enough memory).</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorStream</font></p>
</td>
<td width="72%">
<p><font size="2">Errors reported by the pixel stream subsystem.</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorType</font></p>
</td>
<td width="72%">
<p><font size="2">Errors reported by the type (font) rendering
subsystem.</font></p>
</td>
</tr>
<tr>
<td width="28%">
<p align="center"><font size="2">ErrorXServer</font></p>
</td>
<td width="72%">
<p><font size="2">Errors reported by the X11 subsystem.</font></p>
</td>
</tr>
</table></ul>
<p><br /><br />
</p>
</div>
</body>
</html>
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