	
	
	
	
	
	
	
	
	
Magick::Exception Classes
Exception 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.
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). 
The pseudo code for the main loop of your program may look like: 
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 &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 << “Coder Warning: “ << warning.what() << endl;    }    catch( Magick::Warning &warning )    {      // Handle any other Magick++ warning.      cerr << “Warning: “ << warning.what() << endl;    }    catch( Magick::ErrorFileOpen &error )     {       // Process Magick++ file open error      cerr << “Error: “ << error.what() << endl;      continue; // Try next image.    }    try {      
image.rotate(90);      
image.write(“outfile”);    }    catch ( MagickExeption & error)    {       // Handle problem while rotating or writing outfile.       cerr << “Caught Magick++ exception: “ << error.what() << endl;    }  }  catch( std::exception &error )   
{      
// Process any other exceptions derived from standard C++ exception     err << “Caught C++ STD exception: “ << error.what() << 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    // the program.   
}}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.
The Exception 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.  For
example: 
 catch( Exception &error_ )    {      
cout << "Caught exception: " << error_.what()
<< endl;
    
}
 
The classes Warning and Error derive from the
Exception class. Exceptions derived from Warning 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 
Warningexception may be ignored by catching it immediately, processing it
(e.g. printing a diagnostic) and continuing on. Exceptions derived
from 
Error are thrown to represent fatal errors that can not
produce a valid result (e.g. attempting to read a file which does not
exist). 
The specific derived exception classes
are shown in the following tables: 
Warning Sub-Classes
	
	
	
		
			
Warning
		
		
			
Warning Description
		
	
	
		
			
WarningUndefined
		
		
			
Unspecified warning type.
		
	
	
		
			
WarningBlob
		
		
			
NOT
			CURRENTLY USED
		
	
	
		
			
WarningCache
		
		
			
NOT
			CURRENTLY USED
		
	
	
		
			
WarningCoder
		
		
			
Warnings issued by some coders.
		
	
	
		
			
WarningConfigure
		
		
			
NOT
			CURRENTLY USED
		
	
	
		
			
WarningCorruptImage
		
		
			
Warning issued when an image is determined to be
			corrupt.
		
	
	
		
			
WarningDelegate
		
		
			
Warnings reported by the delegate (interface to
			external programs) subsystem.
		
	
	
		
			
WarningDraw
		
		
			
Warnings reported by the rendering subsystem.
		
	
	
		
			
WarningFileOpen
		
		
			
Warning reported when The image file could not be
			opened (permission problem, wrong file type, or does not exist).
		
	
	
		
			
WarningImage
		
		
			
NOT CURRENTLY USED
		
	
	
		
			
WarningMissingDelegate
		
		
			
NOT CURRENTLY USED
		
	
	
		
			
WarningModule
		
		
			
NOT CURRENTLY USED
		
	
	
		
			
WarningMonitor
		
		
			
NOT CURRENTLY USED
		
	
	
		
			
WarningOption
		
		
			
Warning reported when an option is malformed or
			out of range.
		
	
	
		
			
WarningRegistry
		
		
			
NOT CURRENTLY USED
		
	
	
		
			
WarningResourceLimit
		
		
			
Warning reported when a program resource is
			exhausted (e.g. not enough memory).
		
	
	
		
			
WarningStream
		
		
			
NOT CURRENTLY USED
		
	
	
		
			
WarningType
		
		
			
NOT CURRENTLY USED
		
	
	
		
			
WarningXServer
		
		
			
Warnings reported by the X11 subsystem.
		
	
Error Sub-Classes
	
	
	
		
			
Error
		
		
			
Error Description
		
	
	
		
			
ErrorUndefined
		
		
			
Unspecified error type.
		
	
	
		
			
ErrorBlob
		
		
			
Error reported by BLOB I/O subsystem.
		
	
	
		
			
ErrorCache
		
		
			
Error reported by the pixel cache subsystem.
		
	
	
		
			
ErrorCoder
		
		
			
Error reported by coders (image format support).
		
	
	
		
			
ErrorConfigure
		
		
			
Errors reported while loading configuration files.
		
	
	
		
			
ErrorCorruptImage
		
		
			
Error reported when the image file is corrupt.
		
	
	
		
			
ErrorDelegate
		
		
			
Errors reported by the delegate (interface to
			external programs) subsystem.
		
	
	
		
			
ErrorDraw
		
		
			
Error reported while drawing on image.
		
	
	
		
			
ErrorFileOpen
		
		
			
Error reported when the image file can not be
			opened.
		
	
	
		
			
ErrorImage
		
		
			
Errors reported while drawing.
		
	
	
		
			
ErrorMissingDelegate
		
		
			
Error reported when an add-on library or program
			is necessary in order to support the requested operation.
		
	
	
		
			
ErrorModule
		
		
			
Errors reported by the module loader subsystem.
		
	
	
		
			
ErrorMonitor
		
		
			
NOT CURRENTLY USED
		
	
	
		
			
ErrorOption
		
		
			
Error reported when an option is malformed or out
			of range.
		
	
	
		
			
ErrorRegistry
		
		
			
Errors reported by the image/BLOB registry
			subsystem.
		
	
	
		
			
ErrorResourceLimit
		
		
			
Error reported when a program resource is
			exhausted (e.g. not enough memory).
		
	
	
		
			
ErrorStream
		
		
			
Errors reported by the pixel stream subsystem.
		
	
	
		
			
ErrorType
		
		
			
Errors reported by the type (font) rendering
			subsystem.
		
	
	
		
			
ErrorXServer
		
		
			
Errors reported by the X11 subsystem.
		
	
