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Added 'restore' member function to recover state (multiple times) within a code block

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[SVN r27520]
This commit is contained in:
Daryle Walker
2005-02-28 19:41:10 +00:00
parent 84d932365a
commit 3bcf03e985
2 changed files with 85 additions and 13 deletions
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50
doc/ios_state.html
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@ -131,6 +131,8 @@ class ios_all_word_saver;
explicit saver_class( state_type &s );
saver_class( state_type &amp;s, <var>aspect_type</var> const &amp;new_value );
~saver_class();
void restore();
};
</pre></blockquote>
@ -141,8 +143,9 @@ and not a base class object. The first constructor takes a stream
object and saves a reference to the stream and the current value of a
particular stream attribute. The second constructor works like the
first, and uses its second argument to change the stream's attribute to
the new <var>aspect_type</var> value given. The destructor changes the
stream's attribute back to the saved value.</p>
the new <var>aspect_type</var> value given. The destructor restores the
stream's attribute to the saved value. The restoration can be activated
early (and often) with the <code>restore</code> member function.</p>
<table border="1" align="center">
<caption>Basic IOStreams State Saver Classes</caption>
@ -189,6 +192,8 @@ class <var>saver_class</var>
explicit saver_class( state_type &amp;s );
saver_class( state_type &amp;s, <var>aspect_type</var> const &amp;new_value );
~saver_class();
void restore();
};
</pre></blockquote>
@ -201,8 +206,9 @@ class object. The first constructor takes a stream object and saves a
reference to the stream and the current value of a particular stream
attribute. The second constructor works like the first, and uses its
second argument to change the stream's attribute to the new
<var>aspect_type</var> value given. The destructor changes the stream's
attribute back to the saved value.</p>
<var>aspect_type</var> value given. The destructor restores the stream's
attribute to the saved value. The restoration can be activated
early (and often) with the <code>restore</code> member function.</p>
<table border="1" align="center">
<caption>Advanced IOStreams State Saver Class Templates</caption>
@ -303,6 +309,8 @@ class <var>saver_class</var>
explicit saver_class( state_type &amp;s, index_type i );
saver_class( state_type &amp;s, index_type i, <var>aspect_type</var> const &amp;new_value );
~saver_class();
void restore();
};
</pre></blockquote>
@ -319,7 +327,9 @@ object and index and saves a reference to the stream and the current
value of a particular stream attribute. The second constructor works
like the first, and uses its third argument to change the stream's
attribute to the new <var>aspect_type</var> value given. The destructor
changes the stream's attribute back to the saved value.</p>
restores the stream's attribute to the saved value. The restoration can
be activated early (and often) with the <code>restore</code> member
function.</p>
<table border="1" align="center">
<caption>IOStream User-Defined State Saver Classes</caption>
@ -356,15 +366,20 @@ to have its state preserved. The
<code>boost::io::ios_all_word_saver</code> saver class combines the
saver classes that preserve user-defined formatting information. Its
constructor takes the stream to have its attributes saved and the index
of the user-defined attributes.</p>
of the user-defined attributes. The destructor for each class restores
the saved state. Restoration can be activated early (and often) for a
class with the <code>restore</code> member function.</p>
<h2><a name="example">Example</a></h2>
<p>The code used in the <a href="#rationale">rationale</a> can be
improved at two places. The printing function could use a saver around
the code that changes the formatting state. Or the calling function can
surround the call with a saver. Or both can be done for paranoia's
sake.</p>
surround the call with a saver. Or both can be done, especially if the
user does not know if the printing function uses a state saver. If the
user wants a series of changes back &amp; forth, without surrounding each
change within a separate block, the <code>restore</code> member function
can be called between each trial.</p>
<blockquote><pre>#include &lt;boost/io/ios_state.hpp&gt;
#include &lt;ios&gt;
@ -381,6 +396,7 @@ void new_hex_my_byte( std::ostream &amp;os, char byte )
int main()
{
using std::cout;
using std::cerr;
//...
@ -391,6 +407,16 @@ int main()
}
//...
{
boost::io::ios_all_saver ias( cerr );
new_hex_my_byte( cerr, 'b' );
ias.restore();
new_hex_my_byte( cerr, 'C' );
}
//...
}
</pre></blockquote>
@ -422,15 +448,19 @@ int main()
<h3><a name="history">History</a></h3>
<dl>
<dt>28 Feb 2005, Daryle Walker
<dd>Added the <code>restore</code> member functions, based on suggestions
by Gennadiy Rozental and Rob Stewart
<dt>13 Mar 2002, Daryle Walker
<dd>Initial version
</dl>
<hr>
<p>Revised: 13 March 2002</p>
<p>Revised: 28 February 2005</p>
<p>Copyright 2002 Daryle Walker. Use, modification, and distribution
<p>Copyright 2002, 2005 Daryle Walker. Use, modification, and distribution
are subject to the Boost Software License, Version 1.0. (See accompanying
file <a href="../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or a copy at
&lt;<a href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>&gt;.)</p>