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13<title>Serialization - Archive Exceptions</title>
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16<table border="0" cellpadding="7" cellspacing="0" width="100%" summary="header">
17 <tr>
18 <td valign="top" width="300">
19 <h3><a href="../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../boost.png" border="0"></a></h3>
20 </td>
21 <td valign="top">
22 <h1 align="center">Serialization</h1>
23 <h2 align="center">Archive Exceptions</h2>
24 </td>
25 </tr>
26</table>
27<hr>
28<dl class="page-index">
29 <dt><a href="#unregistered_class"><code style="white-space: normal">unregistered_class</code></a>
30 <dt><a href="#invalid_signature"><code style="white-space: normal">invalid_signature</code></a>
31 <dt><a href="#unsupported_version"><code style="white-space: normal">unsupported_version</code></a>
32 <dt><a href="#unsupported_class_version"><code style="white-space: normal">unsupported_class_version</code></a>
33 <dt><a href="#pointer_conflict"><code style="white-space: normal">pointer_conflict</code></a>
34 <dt><a href="#incompatible_native_format"><code style="white-space: normal">incompatible_native_format</code></a>
35 <dt><a href="#array_size_too_short"><code style="white-space: normal">array_size_too_short</code></a>
36 <dt><a href="#input_stream_error"><code style="white-space: normal">input_stream_error</code></a>
37 <dt><a href="#output_stream_error"><code style="white-space: normal">output_stream_error</code></a>
38 <dt><a href="#invalid_class_name"><code style="white-space: normal">invalid_class_name</code></a>
39 <dt><a href="#unregistered_class"><code style="white-space: normal">unregistered_class</code></a>
40 <dt><a href="#multiple_code_instantiation"><code style="white-space: normal">multiple_code_instantiation</code></a>
41 <dt><a href="#xml_archive_parsing_error"><code style="white-space: normal">xml_archive_parsing_error</code></a>
42 <dt><a href="#xml_archive_tag_mismatch"><code style="white-space: normal">xml_archive_tag_mismatch</code></a>
43 <dt><a href="#xml_archive_tag_name_error"><code style="white-space: normal">xml_archive_tag_name_error</code></a>
44</dl>
45
46Archive operators can throw a <code style="white-space: normal">boost::archive_exception</code>
47object which can be caught by an application program. These exceptions are defined
48in the files <a target="archive_exception_hpp" href="../../../boost/archive/archive_exception.hpp">
49archive_exception.hpp</a>
50and <a target="basic_xml_archive_hpp" href="../../../boost/archive/basic_xml_archive.hpp">
51basic_xml_archive.hpp</a>.
52<pre><code>
53namespace boost {
54namespace archive {
55
56class archive_exception : public std::exception
57{
58public:
59 typedef enum {
60 unregistered_class, // attempt to serialize a pointer of
61 // an unregistered class
62 invalid_signature, // first line of archive does not contain
63 // expected string
64 unsupported_version, // archive created with library version subsequent
65 // to this one
66 pointer_conflict // an attempt has been made to directly serialize
67 // an object after having already serialized the same
68 // object through a pointer. Were this permitted,
69 // the archive load would result in the creation
70 // of an extraneous object.
71 incompatible_native_format, // attempt to read native binary format
72 // on incompatible platform
73 array_size_too_short, // array being loaded doesn't fit in array allocated
74 input_stream_error // error on stream input
75 invalid_class_name, // class name greater than the maximum permitted.
76 // most likely a corrupted archive or an attempt
77 // to insert virus via buffer overrun method.
78 unregistered_cast, // base - derived relationship not registered with
79 // void_cast_register
80 unsupported_class_version, // type saved with a version # greater than the
81 // one used by the program. This indicates that the proggram
82 // needs to be rebuilt.
83 multiple_code_instantiation, // code for implementing serialization for some
84 // type has been instantiated in more than one module.
85 output_stream_error // error on stream output
86 } exception_code;
87 exception_code code;
88 archive_exception(exception_code c) : code(c) {}
89 virtual const char *what( ) const throw();
90};
91
92class xml_archive_exception : public virtual archive_exception
93{
94public:
95 typedef enum {
96 xml_archive_parsing_error, // archive doesn't contain expected data
97 xml_archive_tag_mismatch, // start/end tag in archive doesn't match program
98 xml_archive_tag_name_error // tag name contains invalid characters
99
100 } exception_code;
101 xml_archive_exception(exception_code c){}
102 virtual const char *what( ) const throw();
103};
104
105} // archive
106} // boost
107</code></pre>
108<p>
109<h3><a name="unregistered_class"><code style="white-space: normal">unregistered_class</code></a></h3>
110An attempt has been made to serialize a polymorphic class through a pointer
111without either registering it or associating it with an export key. This can also occur
112when using a new archive whose class name has not been added to the system with the
113<code style="white-space: normal">BOOST_ARCHIVE_CUSTOM_ARCHIVE_TYPES</code> macro.
114
115<h3><a name="invalid_signature"><code style="white-space: normal">invalid_signature</code></a></h3>
116Archives are initiated with a known string. If this string is not found when
117the archive is opened, It is presumed that this file is not a valid archive and this
118exception is thrown.
119
120<h3><a name="unsupported_version"><code style="white-space: normal">unsupported_version</code></a></h3>
121This system records the current library version number to all archives created. Note that this is in
122no way related to version number of classes used by application programs. This refers
123to the version of the serialization system used to create the archive. Future versions
124of this serialization system will be able to identify archives created under a previous
125(i.e. this) system and alter the loading procedure accordingly. Hence, future enhancements
126to this serialization system should not obsolete any existing archive files. It is only
127necessary to increment this version number when the newer system creates archives
128incompatible in format with the current one.
129<p>Should it ever occur that an older program attempts to read newer archives whose
130format has changed, this exception is thrown.
131
132<h3><a name="unsupported_class_version"><code style="white-space: normal">unsupported_class_version</code></a></h3>
133An attempt has been made to load a class whose version has been incremented since the
134program was written. Suppose that a class has been assigned version number 3 and the program
135has been built and sent to third parties. Now suppose that the definition of that class
136has been altered, the version number has been incremented to 4 and new archives have been
137built. If one attempts to load these new archives with the original program, this
138exception will be thrown.
139
140<h3><a name="pointer_conflict"><code style="white-space: normal">pointer_conflict</code></a></h3>
141To understand what this exception means consider the following scenario
142<pre><code>
143template&lt;class Archive&gt;
144void T::save(Archive &ar) const
145{
146 const A * aptr = &a;
147 ar << aptr; // save an instance of object of class A through a pointer
148 ...
149 ar << a; // save an instance of an object of class A
150 assert(aptr == &a); // this must be true
151}
152
153template&lt;class Archive&gt;
154void T::load(Archive &ar)
155{
156 A * aptr;
157 ar >> aptr; // create and initialize a new instance of class A
158 ...
159 ar >> a; // restore state of on object of class A
160 assert(aptr == &a); // this won't be true
161}
162</pre></code>
163An object is saved first through a pointer then directly. Upon loading back
164in the same sequence, we first create an new object and load in its data. Then
165we load the data into another existing object. Where we started with one
166object during save, we have two objects after restore. In a more realistic
167situation, it could be very difficult to find this error. Fortunately,
168these situations can be detected when the archive is created. When
169this occurs, this exception is thrown.
170
171<h3><a name = "incompatible_native_format"><code style="white-space: normal">incompatible_native_format</code></a></h3>
172The library currently supports char text, wide char text and native binary
173archive files. At the beginning of every archive, a signature is written indicating
174the type of archive. This exception is thrown when an attempt is made to read
175an archive written in a different format.
176
177<h3><a name="array_size_too_short"><code style="white-space: normal">array_size_too_short</code></a></h3>
178An attempt has been made to read an array that is larger than the array size.
179This should only occur when the size of an array in code is reduced after an
180archive has already been created.
181
182<h3>
183<a name="input_stream_error"><code style="white-space: normal">input_stream_error</code></a>
184<br>
185<a name="output_stream_error"><code style="white-space: normal">output_stream_error</code></a>
186</h3>
187An error has occured during stream input or ouput. Aside from the common
188situations such as a corrupted or truncated input file, there are
189several less obvious ones that sometimes occur.
190<p>
191This includes
192an attempt to read past the end of the file. Text files need a terminating
193new line character at the end of the file which is appended when the
194archive destructor is invoked. Be sure that an output archive on a stream
195is destroyed before opening an input archive on that same stream. That is,
196rather than using something like:
197<pre><code>
198std::stringstream ss;
199std::vector&lt;V&gt; v;
200boost::archive::text_oarchive oa(ss);
201oa &lt;&lt; v;
202boost::archive::text_iarchive ia(ss);
203ia &gt;&gt; v;
204</code></pre>
205use
206<pre><code>
207std::stringstream ss;
208std::vector&lt;V&gt; v;
209{
210 boost::archive::text_oarchive oa(ss);
211 oa &lt;&lt; v;
212}
213{
214 boost::archive::text_iarchive ia(ss);
215 ia &gt;&gt; v;
216}
217</code></pre>
218<p>
219Another one is the passing of uninitialized data. In general, the behavior
220of the serialization library when passed uninitialized data is undefined.
221If it can be detected, it will invoke an assertion in debug builds.
222Otherwise, depending on the type of archive, it may pass through without
223incident or it may result in an archive with unexpected data in it.
224This, in turn, can result in the throwing of this exception.
225
226<h3><a name="invalid_class_name"><code style="white-space: normal">invalid_class_name</code></a></h3>
227Class name length greater than the maximum permitted. Most likely cause is a corrupted
228archive or an attempt to insert a virus via the buffer overrun method.
229
230<h3><a name="unregistered_cast"><code style="white-space: normal">unregistered_cast</code></a></h3>
231In order to support casting between pointers of base and derived classes
232at runtime, a collection of legitimate conversions is maintained by the system.
233Normally this collection is maintained without any explicit action
234on the part of the user of the library. However, there are special cases
235where this might have to be done explicitly and could be overlooked. This
236is described in <a href="serialization.html#runtimecasting">Runtime Casting</a>.
237This exception is thrown if an attempt is made to convert between two pointers
238whose relationship has not been registered,
239
240<h3><a name="multiple_code_instantiation"><code style="white-space: normal">multiple_code_instantiation</code></a></h3>
241This exception is thrown when it is detected that the serialization of the same type
242has been instantiated more than once. This might occur when
243serialization code is instantiated in both the mainline and one or more DLLS.
244
245<h3><a name="xml_archive_parsing_error"><code style="white-space: normal">xml_archive_parsing_error</code></a></h3>
246The XML generated by the serialization process is intimately coupled to the
247C++ class structure, relationships between objects and the serialization
248specifications. If these become out of sync in any way, the XML may not map
249to the loading serialization and this exception might be thrown. This might
250occur for one of the following reasons:
251<ul>
252 <li>The archive has been edited outside the serialization system. This might
253be possible if only the data is changed and the XML attributes and nesting
254structure are left unaltered. But any other editing is likely to render the
255archive unreadable by the serialization library.
256 <li>The serialization has been altered and an archive generated by the old
257code is being read. That is, versioning has not been properly employed to
258properly deserialize previously created archives.
259</ul>
260
261<h3><a name="xml_archive_tag_mismatch"><code style="white-space: normal">xml_archive_tag_mismatch</code></a></h3>
262This exception will be thrown if the start or end tag of an XML element doesn't match
263the name specified for the object in the program.
264
265<h3><a name="xml_archive_tag_name_error"><code style="white-space: normal">xml_archive_tag_name_error</code></a></h3>
266This exception will be thrown if the tag name contains invalid characters. Valid characters
267for an XML tag are: upper and lower case letters, digits, and the following punctuation: .(period),
268_(underscore), :(colon), and -(hyphen).
269
270<hr>
271<p><i>&copy; Copyright <a href="http://www.rrsd.com">Robert Ramey</a> 2002-2004.
272Distributed under the Boost Software License, Version 1.0. (See
273accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
274</i></p>
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