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<title>RootException</title>
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<p><font size="6" face="Bookman Old Style"><em><strong><u>dtl</u></strong></em></font></p>
<p><img src="stat.gif" width="6" height="6"> <!--end header--> <br>
</p>
<h1>RootException</h1>
<table border="0" cellpadding="0" cellspacing="0" width="100%">
<tr>
<td><img src="exceptions.gif" width="194" height="38"></td>
<td align="right"><img src="type.gif" width="194"
height="39"></td>
</tr>
<tr>
<td valign="top"><b>Category</b>: exceptions</td>
<td align="right" valign="top"><b>Component type</b>:
type</td>
</tr>
</table>
<h3>Description</h3>
<p><tt>RootException</tt> is the base class of all exceptions in
the DTL. An exception of this type stores strings representing
which method the exception was thrown in, a message describing
what error occurred, and what actual exception type was thrown.
The call to the constructor initializes these strings. The user
can extract a stringified message with all of this information
from the exception using the standard <font size="2"
face="Courier New">what() </font><font size="3">method.
Subclasses may also pass in a stringified representation of their
type name as the third argument to the constructor (see below).</font></p>
<h3>Definition</h3>
<p>Defined in the <font size="2" face="Courier New">RootException</font><font
size="1" face="Courier New">.h </font>header file. </p>
<h3>Example: Trivial case of throwing and catching a
RootException</h3>
<p><code>void IWillThrow()<br>
{<br>
vector<int> v(5); <span class="codeComment">// create a vector of 5
elements</span><br>
try<br>
{<br>
for (int i = 0; i <= 5; i++){<br>
v.at(i) = i; <span class="codeComment">// v.at(5) will
throw std::invalid_argument exception</span><br>
}<br>
catch (invalid_argument &ex)<br>
{<br>
<span class="codeComment">// for a method SomeClass::foo(),
method string would be "SomeClass:foo()"</span><br>
<span class="codeComment">// for a global function as
used here, just use its name</span><br>
throw RootException("IWillThrow()",
ex.what());<br>
}<br>
};<br>
<br>
int main()<br>
{<br>
try<br>
{<br>
<span class="codeComment">// call our method which
throws</span><br>
IWillThrow();<br>
}<br>
catch (RootException &ex)<br>
{<br>
<span class="codeComment">// can also say: cout
<< ex << endl;</span><br>
<span class="codeComment">// operator<<() for
RootExceptions just streams out what()</span><br>
cout << ex.what()
<< endl;<br>
}<br>
return 0; <span class="codeComment">// won't reach here ... exception
thrown above</span><br>
}</code></p>
<h3>Model of</h3>
<p>Standard C++ library exception.</p>
<h3>Public base classes</h3>
<p><font size="2" face="Courier New">std::exception</font></p>
<h3>Members</h3>
<table border="2">
<tr>
<th>Member </th>
<th>Where defined </th>
<th>Description </th>
</tr>
<tr>
<td valign="top"><font size="2" face="Courier New">RootException()</font></td>
<td valign="top"><tt>RootException</tt> </td>
<td valign="top"><font size="3">Default constructor. Sets
method and message fields to empty strings and exception
type string to "RootException".</font></td>
</tr>
<tr>
<td valign="top"><font size="2" face="Courier New">RootException(const
string &meth, const string &err, const string
&excType = "RootException")</font></td>
<td valign="top"><tt>RootException</tt> </td>
<td valign="top">Constructor which takes a specific
method, error string, and stringified exception type to
initialize itself.</td>
</tr>
<tr>
<td valign="top"><font size="2" face="Courier New">virtual
const char* what() const throw()</font></td>
<td valign="top"><tt>RootException</tt> </td>
<td valign="top">Overrides behavior in <font size="2"
face="Courier New">std::exception. </font><font size="3">Returns
a C string describing the exception, including the method
it was thrown in, the error message describing why it was
thrown, and what type of exception was thrown. Subclasses
do and may override </font><font size="2"
face="Courier New">what() </font>based on their needs. <font
size="3">See Note </font><a href="#1"><font size="3">[1]</font></a><font
size="3">.</font></td>
</tr>
<tr>
<td valign="top"><tt>friend ostream &operator<<(ostream
&o, const RootException &ex)</tt></td>
<td valign="top"><tt>RootException</tt> </td>
<td valign="top">Note that this is a friend function, and
not a member. Streams out <font size="2"
face="Courier New">ex.what()</font><font size="3"> to </font><font
size="2" face="Courier New">o.</font><font size="3"> As </font><font
size="2" face="Courier New">what() </font><font size="3">is
virtual, the appropriate version of that method will be
called for </font><font size="2" face="Courier New">ex.</font></td>
</tr>
</table>
<h3>Notes</h3>
<p><a name="1"></a>[1] A <tt>RootException</tt> contains a
protected <font size="2" face="Courier New">string </font><font
size="3">member named </font><font size="2" face="Courier New">whatbuf.
</font><font size="3">This seemingly extra member is needed as
the </font><font size="2" face="Courier New">std::exception </font><font
size="3">does not contain a <strong>portable</strong>, <strong>mutable
</strong>way to access its own member that is used to hold the
error message. This effects the implementation of the </font><font
size="2" face="Courier New">what() </font><font size="3">method
as the exception needs a way to build its own error string,
possibly partly based on what the superclass exception does in
its work. An example of how to implement </font><font size="2"
face="Courier New">what() </font><font size="3">for a subclass of
</font><tt>RootException </tt><font size="4"
face="Times New Roman"><tt>can be found in the </tt></font><font
size="3"><tt>DBException</tt></font><font size="4"
face="Times New Roman"><tt> class:</tt></font></p>
<p><font size="3"><tt>// DBException::what() ... DBException
derives from RootException<br>
virtual const char *what() const throw()<br>
{<br>
string rootWhat = RootException::what(); // let
RootException build up the common part of the error string<br>
ostringstream o;<br>
o << rootWhat;<br>
<br>
// stream out ODBC errors to the what() string<br>
if (sqlErrors.size() > 0)<br>
{<br>
o << "SQL Errors:
" << endl;<br>
<br>
for (size_t i = 0; i <
sqlErrors.size(); i++)<br>
{<br>
o <<
"(" << i << ") " <<
sqlErrors[i] << endl;<br>
}<br>
<br>
}<br>
<br>
// this gymnastics is needed so result isn't
destroyed<br>
// paste these two lines into all what() code<br>
whatbuf = o.str();<br>
return whatbuf.c_str();<br>
}<br>
</tt></font></p>
<h3>See also</h3>
<p><a href="DBException.htm"><font size="2" face="Courier New">DBException</font></a>,
<a href="ETIException.htm"><font size="2" face="Courier New">ETIException,</font></a>
<a href="ValidityException.htm"><font size="2" face="Courier New">ValidityException</font></a>,
<a href="VariantException.htm"><font size="2" face="Courier New">VariantException</font></a>.<br>
<br>
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