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<a name="declval"></a>Declval</h2></div>
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<div><div class="authorgroup">
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<div class="author"><h3 class="author">
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<span class="firstname">Howard</span> <span class="surname">Hinnant</span>
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</h3></div>
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<div class="author"><h3 class="author">
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<span class="firstname">Vicente J.</span> <span class="surname">Botet Escriba</span>
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</h3></div>
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</div></div>
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<div><p class="copyright">Copyright © 2008 Howard Hinnant</p></div>
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<div><p class="copyright">Copyright © 2009-2012 Vicente
|
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J. Botet Escriba</p></div>
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<div><div class="legalnotice">
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<a name="declval.legal"></a><p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
|
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file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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<hr>
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</div>
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<div class="toc">
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<p><b>Table of Contents</b></p>
|
||||
<dl class="toc">
|
||||
<dt><span class="section"><a href="declval.html#declval.overview">Overview</a></span></dt>
|
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<dt><span class="section"><a href="declval.html#declval.reference">Reference </a></span></dt>
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<dt><span class="section"><a href="declval.html#declval.history">History</a></span></dt>
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</dl>
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</div>
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<div class="section">
|
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="declval.overview"></a><a class="link" href="declval.html#declval.overview" title="Overview">Overview</a>
|
||||
</h2></div></div></div>
|
||||
<p>
|
||||
The motivation for <code class="computeroutput"><span class="identifier">declval</span></code>
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||||
was introduced in <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2958.html#Value" target="_top">N2958:
|
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Moving Swap Forward</a>. Here follows a rewording of this chapter.
|
||||
</p>
|
||||
<p>
|
||||
With the provision of decltype, late-specified return types, and default template-arguments
|
||||
for function templates a new generation of SFINAE patterns will emerge to at
|
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least partially compensate the lack of concepts on the C++0x timescale. Using
|
||||
this technique, it is sometimes necessary to obtain an object of a known type
|
||||
in a non-using context, e.g. given the declaration
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
|
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<span class="identifier">T</span><span class="special">&&</span> <span class="identifier">declval</span><span class="special">();</span> <span class="comment">// not used</span>
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</pre>
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||||
<p>
|
||||
as part of the function template declaration
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">To</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">From</span><span class="special">></span>
|
||||
<span class="keyword">decltype</span><span class="special">(</span><span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">To</span><span class="special">>(</span><span class="identifier">declval</span><span class="special"><</span><span class="identifier">From</span><span class="special">>()))</span> <span class="identifier">convert</span><span class="special">(</span><span class="identifier">From</span><span class="special">&&);</span>
|
||||
</pre>
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||||
<p>
|
||||
or as part of a class template definition
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">></span> <span class="keyword">class</span> <span class="identifier">result_of</span><span class="special">;</span>
|
||||
|
||||
<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Fn</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">ArgTypes</span><span class="special">></span>
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||||
<span class="keyword">struct</span> <span class="identifier">result_of</span><span class="special"><</span><span class="identifier">Fn</span><span class="special">(</span><span class="identifier">ArgTypes</span><span class="special">...)></span>
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||||
<span class="special">{</span>
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<span class="keyword">typedef</span> <span class="keyword">decltype</span><span class="special">(</span><span class="identifier">declval</span><span class="special"><</span><span class="identifier">Fn</span><span class="special">>()(</span><span class="identifier">declval</span><span class="special"><</span><span class="identifier">ArgTypes</span><span class="special">>()...))</span> <span class="identifier">type</span><span class="special">;</span>
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<span class="special">};</span>
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</pre>
|
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<p>
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The role of the function template declval() is a transformation of a type T
|
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into a value without using or evaluating this function. The name is supposed
|
||||
to direct the reader's attention to the fact that the expression <code class="computeroutput"><span class="identifier">declval</span><span class="special"><</span><span class="identifier">T</span><span class="special">>()</span></code> is
|
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an lvalue if and only if T is an lvalue-reference, otherwise an rvalue. To
|
||||
extend the domain of this function we can do a bit better by changing its declaration
|
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to
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
|
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<span class="keyword">typename</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">add_rvalue_reference</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">declval</span><span class="special">();</span> <span class="comment">// not used</span>
|
||||
</pre>
|
||||
<p>
|
||||
which ensures that we can also use cv void as template parameter. The careful
|
||||
reader might have noticed that <code class="computeroutput"><span class="identifier">declval</span><span class="special">()</span></code> already exists under the name create() as
|
||||
part of the definition of the semantics of the type trait is_convertible in
|
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the C++0x standard.
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</p>
|
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<p>
|
||||
The provision of a new library component that allows the production of values
|
||||
in unevaluated expressions is considered important to realize constrained templates
|
||||
in C++0x where concepts are not available. This extremely light-weight function
|
||||
is expected to be part of the daily tool-box of the C++0x programmer.
|
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</p>
|
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="declval.reference"></a><a class="link" href="declval.html#declval.reference" title="Reference">Reference </a>
|
||||
</h2></div></div></div>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">utility</span><span class="special">/</span><span class="identifier">declval</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
|
||||
|
||||
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span>
|
||||
<span class="keyword">typename</span> <span class="identifier">add_rvalue_reference</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">declval</span><span class="special">()</span> <span class="keyword">noexcept</span><span class="special">;</span> <span class="comment">// as unevaluated operand</span>
|
||||
|
||||
<span class="special">}</span> <span class="comment">// namespace boost</span>
|
||||
</pre>
|
||||
<p>
|
||||
The library provides the function template declval to simplify the definition
|
||||
of expressions which occur as unevaluated operands.
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span>
|
||||
<span class="keyword">typename</span> <span class="identifier">add_rvalue_reference</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">declval</span><span class="special">();</span>
|
||||
</pre>
|
||||
<p>
|
||||
<span class="bold"><strong>Remarks:</strong></span> If this function is used, the program
|
||||
is ill-formed.
|
||||
</p>
|
||||
<p>
|
||||
<span class="bold"><strong>Remarks:</strong></span> The template parameter T of declval
|
||||
may be an incomplete type.
|
||||
</p>
|
||||
<p>
|
||||
<span class="bold"><strong>Example:</strong></span>
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">To</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">From</span><span class="special">></span>
|
||||
<span class="keyword">decltype</span><span class="special">(</span><span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">To</span><span class="special">>(</span><span class="identifier">declval</span><span class="special"><</span><span class="identifier">From</span><span class="special">>()))</span> <span class="identifier">convert</span><span class="special">(</span><span class="identifier">From</span><span class="special">&&);</span>
|
||||
</pre>
|
||||
<p>
|
||||
Declares a function template convert which only participates in overloading
|
||||
if the type From can be explicitly converted to type To.
|
||||
</p>
|
||||
</div>
|
||||
<div class="section">
|
||||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||||
<a name="declval.history"></a><a class="link" href="declval.html#declval.history" title="History">History</a>
|
||||
</h2></div></div></div>
|
||||
<h4>
|
||||
<a name="declval.history.h0"></a>
|
||||
<span class="phrase"><a name="declval.history.boost_1_50"></a></span><a class="link" href="declval.html#declval.history.boost_1_50">boost
|
||||
1.50</a>
|
||||
</h4>
|
||||
<p>
|
||||
Fixes:
|
||||
</p>
|
||||
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
|
||||
<a href="http://svn.boost.org/trac/boost/ticket/6570" target="_top">#6570</a>
|
||||
Adding noexcept to boost::declval.
|
||||
</li></ul></div>
|
||||
</div>
|
||||
</div>
|
||||
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
|
||||
<td align="left"><p><small>Last revised: November 23, 2013 at 14:11:12 GMT</small></p></td>
|
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<a name="string_ref"></a>String_Ref</h2></div>
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<div><div class="authorgroup"><div class="author"><h3 class="author">
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<span class="firstname">Marshall</span> <span class="surname">Clow</span>
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</h3></div></div></div>
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<div><p class="copyright">Copyright © 2012 Marshall Clow</p></div>
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<div><div class="legalnotice">
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<a name="string_ref.legal"></a><p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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<hr>
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</div>
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<div class="toc">
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<p><b>Table of Contents</b></p>
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<dl class="toc">
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<dt><span class="section"><a href="string_ref.html#string_ref.overview">Overview</a></span></dt>
|
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<dt><span class="section"><a href="string_ref.html#string_ref.examples">Examples</a></span></dt>
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<dt><span class="section"><a href="string_ref.html#string_ref.reference">Reference </a></span></dt>
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<dt><span class="section"><a href="string_ref.html#string_ref.history">History</a></span></dt>
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="string_ref.overview"></a><a class="link" href="string_ref.html#string_ref.overview" title="Overview">Overview</a>
|
||||
</h2></div></div></div>
|
||||
<p>
|
||||
Boost.StringRef is an implementation of Jeffrey Yaskin's <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3442.html" target="_top">N3442:
|
||||
string_ref: a non-owning reference to a string</a>.
|
||||
</p>
|
||||
<p>
|
||||
When you are parsing/processing strings from some external source, frequently
|
||||
you want to pass a piece of text to a procedure for specialized processing.
|
||||
The canonical way to do this is as a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>,
|
||||
but that has certain drawbacks:
|
||||
</p>
|
||||
<p>
|
||||
1) If you are processing a buffer of text (say a HTTP response or the contents
|
||||
of a file), then you have to create the string from the text you want to pass,
|
||||
which involves memory allocation and copying of data.
|
||||
</p>
|
||||
<p>
|
||||
2) if a routine receives a constant <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>
|
||||
and wants to pass a portion of that string to another routine, then it must
|
||||
create a new string of that substring.
|
||||
</p>
|
||||
<p>
|
||||
3) A routine receives a constant <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>
|
||||
and wants to return a portion of the string, then it must create a new string
|
||||
to return.
|
||||
</p>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">string_ref</span></code> is designed to solve
|
||||
these efficiency problems. A <code class="computeroutput"><span class="identifier">string_ref</span></code>
|
||||
is a read-only reference to a contiguous sequence of characters, and provides
|
||||
much of the functionality of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>.
|
||||
A <code class="computeroutput"><span class="identifier">string_ref</span></code> is cheap to create,
|
||||
copy and pass by value, because it does not actually own the storage that it
|
||||
points to.
|
||||
</p>
|
||||
<p>
|
||||
A <code class="computeroutput"><span class="identifier">string_ref</span></code> is implemented
|
||||
as a small struct that contains a pointer to the start of the character data
|
||||
and a count. A <code class="computeroutput"><span class="identifier">string_ref</span></code> is
|
||||
cheap to create and cheap to copy.
|
||||
</p>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">string_ref</span></code> acts as a container;
|
||||
it includes all the methods that you would expect in a container, including
|
||||
iteration support, <code class="computeroutput"><span class="keyword">operator</span> <span class="special">[]</span></code>,
|
||||
<code class="computeroutput"><span class="identifier">at</span></code> and <code class="computeroutput"><span class="identifier">size</span></code>.
|
||||
It can be used with any of the iterator-based algorithms in the STL - as long
|
||||
as you don't need to change the underlying data (<code class="computeroutput"><span class="identifier">sort</span></code>
|
||||
and <code class="computeroutput"><span class="identifier">remove</span></code>, for example, will
|
||||
not work)
|
||||
</p>
|
||||
<p>
|
||||
Besides generic container functionality, <code class="computeroutput"><span class="identifier">string_ref</span></code>
|
||||
provides a subset of the interface of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>.
|
||||
This makes it easy to replace parameters of type <code class="computeroutput"><span class="keyword">const</span>
|
||||
<span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">&</span></code>
|
||||
with <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">string_ref</span></code>. Like <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>,
|
||||
<code class="computeroutput"><span class="identifier">string_ref</span></code> has a static member
|
||||
variable named <code class="computeroutput"><span class="identifier">npos</span></code> to denote
|
||||
the result of failed searches, and to mean "the end".
|
||||
</p>
|
||||
<p>
|
||||
Because a <code class="computeroutput"><span class="identifier">string_ref</span></code> does not
|
||||
own the data that it "points to", it introduces lifetime issues into
|
||||
code that uses it. The programmer must ensure that the data that a <code class="computeroutput"><span class="identifier">string_ref</span></code> refers to exists as long as the
|
||||
<code class="computeroutput"><span class="identifier">string_ref</span></code> does.
|
||||
</p>
|
||||
</div>
|
||||
<div class="section">
|
||||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||||
<a name="string_ref.examples"></a><a class="link" href="string_ref.html#string_ref.examples" title="Examples">Examples</a>
|
||||
</h2></div></div></div>
|
||||
<p>
|
||||
Integrating <code class="computeroutput"><span class="identifier">string_ref</span></code> into
|
||||
your code is fairly simple. Wherever you pass a <code class="computeroutput"><span class="keyword">const</span>
|
||||
<span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">&</span></code>
|
||||
or <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code> as a parameter, that's a candidate
|
||||
for passing a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">string_ref</span></code>.
|
||||
</p>
|
||||
<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">extract_part</span> <span class="special">(</span> <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">&</span><span class="identifier">bar</span> <span class="special">)</span> <span class="special">{</span>
|
||||
<span class="keyword">return</span> <span class="identifier">bar</span><span class="special">.</span><span class="identifier">substr</span> <span class="special">(</span> <span class="number">2</span><span class="special">,</span> <span class="number">3</span> <span class="special">);</span>
|
||||
<span class="special">}</span>
|
||||
|
||||
<span class="keyword">if</span> <span class="special">(</span> <span class="identifier">extract_part</span> <span class="special">(</span> <span class="string">"ABCDEFG"</span> <span class="special">).</span><span class="identifier">front</span><span class="special">()</span> <span class="special">==</span> <span class="char">'C'</span> <span class="special">)</span> <span class="special">{</span> <span class="comment">/* do something */</span> <span class="special">}</span>
|
||||
</pre>
|
||||
<p>
|
||||
Let's figure out what happens in this (contrived) example.
|
||||
</p>
|
||||
<p>
|
||||
First, a temporary string is created from the string literal <code class="computeroutput"><span class="string">"ABCDEFG"</span></code>, and it is passed (by reference)
|
||||
to the routine <code class="computeroutput"><span class="identifier">extract_part</span></code>.
|
||||
Then a second string is created in the call <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">::</span><span class="identifier">substr</span></code>
|
||||
and returned to <code class="computeroutput"><span class="identifier">extract_part</span></code>
|
||||
(this copy may be elided by RVO). Then <code class="computeroutput"><span class="identifier">extract_part</span></code>
|
||||
returns that string back to the caller (again this copy may be elided). The
|
||||
first temporary string is deallocated, and <code class="computeroutput"><span class="identifier">front</span></code>
|
||||
is called on the second string, and then it is deallocated as well.
|
||||
</p>
|
||||
<p>
|
||||
Two <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>s are created, and two copy operations.
|
||||
That's (potentially) four memory allocations and deallocations, and the associated
|
||||
copying of data.
|
||||
</p>
|
||||
<p>
|
||||
Now let's look at the same code with <code class="computeroutput"><span class="identifier">string_ref</span></code>:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">string_ref</span> <span class="identifier">extract_part</span> <span class="special">(</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">string_ref</span> <span class="identifier">bar</span> <span class="special">)</span> <span class="special">{</span>
|
||||
<span class="keyword">return</span> <span class="identifier">bar</span><span class="special">.</span><span class="identifier">substr</span> <span class="special">(</span> <span class="number">2</span><span class="special">,</span> <span class="number">3</span> <span class="special">);</span>
|
||||
<span class="special">}</span>
|
||||
|
||||
<span class="keyword">if</span> <span class="special">(</span> <span class="identifier">extract_part</span> <span class="special">(</span> <span class="string">"ABCDEFG"</span> <span class="special">).</span><span class="identifier">front</span><span class="special">()</span> <span class="special">==</span> <span class="string">"C"</span> <span class="special">)</span> <span class="special">{</span> <span class="comment">/* do something */</span> <span class="special">}</span>
|
||||
</pre>
|
||||
<p>
|
||||
No memory allocations. No copying of character data. No changes to the code
|
||||
other than the types. There are two <code class="computeroutput"><span class="identifier">string_ref</span></code>s
|
||||
created, and two <code class="computeroutput"><span class="identifier">string_ref</span></code>s
|
||||
copied, but those are cheap operations.
|
||||
</p>
|
||||
</div>
|
||||
<div class="section">
|
||||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||||
<a name="string_ref.reference"></a><a class="link" href="string_ref.html#string_ref.reference" title="Reference">Reference </a>
|
||||
</h2></div></div></div>
|
||||
<p>
|
||||
The header file "string_ref.hpp" defines a template <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">basic_string_ref</span></code>,
|
||||
and four specializations - for <code class="computeroutput"><span class="keyword">char</span></code>
|
||||
/ <code class="computeroutput"><span class="keyword">wchar_t</span></code> / <code class="computeroutput"><span class="keyword">char16_t</span></code>
|
||||
/ <code class="computeroutput"><span class="keyword">char32_t</span></code> .
|
||||
</p>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">utility</span><span class="special">/</span><span class="identifier">string_ref</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
|
||||
</p>
|
||||
<p>
|
||||
Construction and copying:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="identifier">BOOST_CONSTEXPR</span> <span class="identifier">basic_string_ref</span> <span class="special">();</span> <span class="comment">// Constructs an empty string_ref</span>
|
||||
<span class="identifier">BOOST_CONSTEXPR</span> <span class="identifier">basic_string_ref</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">charT</span><span class="special">*</span> <span class="identifier">str</span><span class="special">);</span> <span class="comment">// Constructs from a NULL-terminated string</span>
|
||||
<span class="identifier">BOOST_CONSTEXPR</span> <span class="identifier">basic_string_ref</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">charT</span><span class="special">*</span> <span class="identifier">str</span><span class="special">,</span> <span class="identifier">size_type</span> <span class="identifier">len</span><span class="special">);</span> <span class="comment">// Constructs from a pointer, length pair</span>
|
||||
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Allocator</span><span class="special">></span>
|
||||
<span class="identifier">basic_string_ref</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_string</span><span class="special"><</span><span class="identifier">charT</span><span class="special">,</span> <span class="identifier">traits</span><span class="special">,</span> <span class="identifier">Allocator</span><span class="special">>&</span> <span class="identifier">str</span><span class="special">);</span> <span class="comment">// Constructs from a std::string</span>
|
||||
<span class="identifier">basic_string_ref</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">basic_string_ref</span> <span class="special">&</span><span class="identifier">rhs</span><span class="special">);</span>
|
||||
<span class="identifier">basic_string_ref</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span><span class="keyword">const</span> <span class="identifier">basic_string_ref</span> <span class="special">&</span><span class="identifier">rhs</span><span class="special">);</span>
|
||||
</pre>
|
||||
<p>
|
||||
<code class="computeroutput"><span class="identifier">string_ref</span></code> does not define
|
||||
a move constructor nor a move-assignment operator because copying a <code class="computeroutput"><span class="identifier">string_ref</span></code> is just a cheap as moving one.
|
||||
</p>
|
||||
<p>
|
||||
Basic container-like functions:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="identifier">BOOST_CONSTEXPR</span> <span class="identifier">size_type</span> <span class="identifier">size</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">BOOST_CONSTEXPR</span> <span class="identifier">size_type</span> <span class="identifier">length</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">BOOST_CONSTEXPR</span> <span class="identifier">size_type</span> <span class="identifier">max_size</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">BOOST_CONSTEXPR</span> <span class="keyword">bool</span> <span class="identifier">empty</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
|
||||
<span class="comment">// All iterators are const_iterators</span>
|
||||
<span class="identifier">BOOST_CONSTEXPR</span> <span class="identifier">const_iterator</span> <span class="identifier">begin</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">BOOST_CONSTEXPR</span> <span class="identifier">const_iterator</span> <span class="identifier">cbegin</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">BOOST_CONSTEXPR</span> <span class="identifier">const_iterator</span> <span class="identifier">end</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">BOOST_CONSTEXPR</span> <span class="identifier">const_iterator</span> <span class="identifier">cend</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">const_reverse_iterator</span> <span class="identifier">rbegin</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">const_reverse_iterator</span> <span class="identifier">crbegin</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">const_reverse_iterator</span> <span class="identifier">rend</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">const_reverse_iterator</span> <span class="identifier">crend</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
</pre>
|
||||
<p>
|
||||
Access to the individual elements (all of which are const):
|
||||
</p>
|
||||
<pre class="programlisting"><span class="identifier">BOOST_CONSTEXPR</span> <span class="keyword">const</span> <span class="identifier">charT</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">[](</span><span class="identifier">size_type</span> <span class="identifier">pos</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="keyword">const</span> <span class="identifier">charT</span><span class="special">&</span> <span class="identifier">at</span><span class="special">(</span><span class="identifier">size_t</span> <span class="identifier">pos</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">BOOST_CONSTEXPR</span> <span class="keyword">const</span> <span class="identifier">charT</span><span class="special">&</span> <span class="identifier">front</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">BOOST_CONSTEXPR</span> <span class="keyword">const</span> <span class="identifier">charT</span><span class="special">&</span> <span class="identifier">back</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">BOOST_CONSTEXPR</span> <span class="keyword">const</span> <span class="identifier">charT</span><span class="special">*</span> <span class="identifier">data</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
</pre>
|
||||
<p>
|
||||
Modifying the <code class="computeroutput"><span class="identifier">string_ref</span></code> (but
|
||||
not the underlying data):
|
||||
</p>
|
||||
<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">clear</span><span class="special">();</span>
|
||||
<span class="keyword">void</span> <span class="identifier">remove_prefix</span><span class="special">(</span><span class="identifier">size_type</span> <span class="identifier">n</span><span class="special">);</span>
|
||||
<span class="keyword">void</span> <span class="identifier">remove_suffix</span><span class="special">(</span><span class="identifier">size_type</span> <span class="identifier">n</span><span class="special">);</span>
|
||||
</pre>
|
||||
<p>
|
||||
Searching:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="identifier">size_type</span> <span class="identifier">find</span><span class="special">(</span><span class="identifier">basic_string_ref</span> <span class="identifier">s</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">size_type</span> <span class="identifier">find</span><span class="special">(</span><span class="identifier">charT</span> <span class="identifier">c</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">size_type</span> <span class="identifier">rfind</span><span class="special">(</span><span class="identifier">basic_string_ref</span> <span class="identifier">s</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">size_type</span> <span class="identifier">rfind</span><span class="special">(</span><span class="identifier">charT</span> <span class="identifier">c</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">size_type</span> <span class="identifier">find_first_of</span><span class="special">(</span><span class="identifier">charT</span> <span class="identifier">c</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">size_type</span> <span class="identifier">find_last_of</span> <span class="special">(</span><span class="identifier">charT</span> <span class="identifier">c</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
|
||||
<span class="identifier">size_type</span> <span class="identifier">find_first_of</span><span class="special">(</span><span class="identifier">basic_string_ref</span> <span class="identifier">s</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">size_type</span> <span class="identifier">find_last_of</span><span class="special">(</span><span class="identifier">basic_string_ref</span> <span class="identifier">s</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">size_type</span> <span class="identifier">find_first_not_of</span><span class="special">(</span><span class="identifier">basic_string_ref</span> <span class="identifier">s</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">size_type</span> <span class="identifier">find_first_not_of</span><span class="special">(</span><span class="identifier">charT</span> <span class="identifier">c</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">size_type</span> <span class="identifier">find_last_not_of</span><span class="special">(</span><span class="identifier">basic_string_ref</span> <span class="identifier">s</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="identifier">size_type</span> <span class="identifier">find_last_not_of</span><span class="special">(</span><span class="identifier">charT</span> <span class="identifier">c</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
</pre>
|
||||
<p>
|
||||
String-like operations:
|
||||
</p>
|
||||
<pre class="programlisting"><span class="identifier">BOOST_CONSTEXPR</span> <span class="identifier">basic_string_ref</span> <span class="identifier">substr</span><span class="special">(</span><span class="identifier">size_type</span> <span class="identifier">pos</span><span class="special">,</span> <span class="identifier">size_type</span> <span class="identifier">n</span><span class="special">=</span><span class="identifier">npos</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span> <span class="comment">// Creates a new string_ref</span>
|
||||
<span class="keyword">bool</span> <span class="identifier">starts_with</span><span class="special">(</span><span class="identifier">charT</span> <span class="identifier">c</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="keyword">bool</span> <span class="identifier">starts_with</span><span class="special">(</span><span class="identifier">basic_string_ref</span> <span class="identifier">x</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="keyword">bool</span> <span class="identifier">ends_with</span><span class="special">(</span><span class="identifier">charT</span> <span class="identifier">c</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
<span class="keyword">bool</span> <span class="identifier">ends_with</span><span class="special">(</span><span class="identifier">basic_string_ref</span> <span class="identifier">x</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span>
|
||||
</pre>
|
||||
</div>
|
||||
<div class="section">
|
||||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||||
<a name="string_ref.history"></a><a class="link" href="string_ref.html#string_ref.history" title="History">History</a>
|
||||
</h2></div></div></div>
|
||||
<h4>
|
||||
<a name="string_ref.history.h0"></a>
|
||||
<span class="phrase"><a name="string_ref.history.boost_1_53"></a></span><a class="link" href="string_ref.html#string_ref.history.boost_1_53">boost
|
||||
1.53</a>
|
||||
</h4>
|
||||
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
|
||||
Introduced
|
||||
</li></ul></div>
|
||||
</div>
|
||||
</div>
|
||||
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
|
||||
<td align="left"><p><small>Last revised: November 23, 2013 at 14:12:56 GMT</small></p></td>
|
||||
<td align="right"><div class="copyright-footer"></div></td>
|
||||
</tr></table>
|
||||
<hr>
|
||||
<div class="spirit-nav"></div>
|
||||
</body>
|
||||
</html>
|
||||
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Reference in New Issue
Block a user