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| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="intrusive.advanced_lookups_insertions"></a><a class="link" href="advanced_lookups_insertions.html" title="Advanced lookup and insertion functions for associative containers">Advanced lookup |
| and insertion functions for associative containers</a> |
| </h2></div></div></div> |
| <div class="toc"><dl> |
| <dt><span class="section"><a href="advanced_lookups_insertions.html#intrusive.advanced_lookups_insertions.advanced_lookups">Advanced |
| lookups</a></span></dt> |
| <dt><span class="section"><a href="advanced_lookups_insertions.html#intrusive.advanced_lookups_insertions.advanced_insertions">Advanced |
| insertions</a></span></dt> |
| <dt><span class="section"><a href="advanced_lookups_insertions.html#intrusive.advanced_lookups_insertions.positional_insertions">Positional |
| insertions</a></span></dt> |
| </dl></div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="intrusive.advanced_lookups_insertions.advanced_lookups"></a><a class="link" href="advanced_lookups_insertions.html#intrusive.advanced_lookups_insertions.advanced_lookups" title="Advanced lookups">Advanced |
| lookups</a> |
| </h3></div></div></div> |
| <p> |
| <span class="bold"><strong>Boost.Intrusive</strong></span> associative containers offer |
| the same interface as STL associative containers. However, STL and TR1 ordered |
| and unordered simple associative containers (<code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">set</span></code>, |
| <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">multiset</span></code>, <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">tr1</span><span class="special">::</span><span class="identifier">unordered_set</span></code> and <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">tr1</span><span class="special">::</span><span class="identifier">unordered_multiset</span></code>) have some inefficiencies |
| caused by the interface: the user can only operate with <code class="computeroutput"><span class="identifier">value_type</span></code> |
| objects. When using these containers we must use <code class="computeroutput"><span class="identifier">iterator</span> |
| <span class="identifier">find</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">value_type</span> |
| <span class="special">&</span><span class="identifier">value</span><span class="special">)</span></code> to find a value. The same happens in other |
| functions like <code class="computeroutput"><span class="identifier">equal_range</span></code>, |
| <code class="computeroutput"><span class="identifier">lower_bound</span></code>, <code class="computeroutput"><span class="identifier">upper_bound</span></code>, etc. |
| </p> |
| <p> |
| However, sometimes the object to be searched is quite expensive to construct: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">intrusive</span><span class="special">/</span><span class="identifier">set</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">intrusive</span><span class="special">/</span><span class="identifier">unordered_set</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cstring</span><span class="special">></span> |
| |
| <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">intrusive</span><span class="special">;</span> |
| |
| <span class="comment">// Hash function for strings |
| </span><span class="keyword">struct</span> <span class="identifier">StrHasher</span> |
| <span class="special">{</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">str</span><span class="special">)</span> <span class="keyword">const</span> |
| <span class="special">{</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">seed</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> |
| <span class="keyword">for</span><span class="special">(;</span> <span class="special">*</span><span class="identifier">str</span><span class="special">;</span> <span class="special">++</span><span class="identifier">str</span><span class="special">)</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">hash_combine</span><span class="special">(</span><span class="identifier">seed</span><span class="special">,</span> <span class="special">*</span><span class="identifier">str</span><span class="special">);</span> |
| <span class="keyword">return</span> <span class="identifier">seed</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">};</span> |
| |
| <span class="keyword">class</span> <span class="identifier">Expensive</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">set_base_hook</span><span class="special"><>,</span> <span class="keyword">public</span> <span class="identifier">unordered_set_base_hook</span><span class="special"><></span> |
| <span class="special">{</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">key_</span><span class="special">;</span> |
| <span class="comment">// Other members... |
| </span> |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="identifier">Expensive</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">key</span><span class="special">)</span> |
| <span class="special">:</span> <span class="identifier">key_</span><span class="special">(</span><span class="identifier">key</span><span class="special">)</span> |
| <span class="special">{}</span> <span class="comment">//other expensive initializations... |
| </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">get_key</span><span class="special">()</span> <span class="keyword">const</span> |
| <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">key_</span><span class="special">;</span> <span class="special">}</span> |
| |
| <span class="keyword">friend</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special"><</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">Expensive</span> <span class="special">&</span><span class="identifier">a</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">Expensive</span> <span class="special">&</span><span class="identifier">b</span><span class="special">)</span> |
| <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">a</span><span class="special">.</span><span class="identifier">key_</span> <span class="special"><</span> <span class="identifier">b</span><span class="special">.</span><span class="identifier">key_</span><span class="special">;</span> <span class="special">}</span> |
| |
| <span class="keyword">friend</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">==</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">Expensive</span> <span class="special">&</span><span class="identifier">a</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">Expensive</span> <span class="special">&</span><span class="identifier">b</span><span class="special">)</span> |
| <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">a</span><span class="special">.</span><span class="identifier">key_</span> <span class="special">==</span> <span class="identifier">b</span><span class="special">.</span><span class="identifier">key_</span><span class="special">;</span> <span class="special">}</span> |
| |
| <span class="keyword">friend</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">hash_value</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Expensive</span> <span class="special">&</span><span class="identifier">object</span><span class="special">)</span> |
| <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">StrHasher</span><span class="special">()(</span><span class="identifier">object</span><span class="special">.</span><span class="identifier">get_key</span><span class="special">().</span><span class="identifier">c_str</span><span class="special">());</span> <span class="special">}</span> |
| <span class="special">};</span> |
| |
| <span class="comment">// A set and unordered_set that store Expensive objects |
| </span><span class="keyword">typedef</span> <span class="identifier">set</span><span class="special"><</span><span class="identifier">Expensive</span><span class="special">></span> <span class="identifier">Set</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">unordered_set</span><span class="special"><</span><span class="identifier">Expensive</span><span class="special">></span> <span class="identifier">UnorderedSet</span><span class="special">;</span> |
| |
| <span class="comment">// Search functions |
| </span><span class="identifier">Expensive</span> <span class="special">*</span><span class="identifier">get_from_set</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">key</span><span class="special">,</span> <span class="identifier">Set</span> <span class="special">&</span><span class="identifier">set_object</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">Set</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">it</span> <span class="special">=</span> <span class="identifier">set_object</span><span class="special">.</span><span class="identifier">find</span><span class="special">(</span><span class="identifier">Expensive</span><span class="special">(</span><span class="identifier">key</span><span class="special">));</span> |
| <span class="keyword">if</span><span class="special">(</span> <span class="identifier">it</span> <span class="special">==</span> <span class="identifier">set_object</span><span class="special">.</span><span class="identifier">end</span><span class="special">()</span> <span class="special">)</span> <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="keyword">return</span> <span class="special">&*</span><span class="identifier">it</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="identifier">Expensive</span> <span class="special">*</span><span class="identifier">get_from_uset</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">key</span><span class="special">,</span> <span class="identifier">UnorderedSet</span> <span class="special">&</span><span class="identifier">uset_object</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">UnorderedSet</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">it</span> <span class="special">=</span> <span class="identifier">uset_object</span><span class="special">.</span><span class="identifier">find</span><span class="special">(</span><span class="identifier">Expensive</span> <span class="special">(</span><span class="identifier">key</span><span class="special">));</span> |
| <span class="keyword">if</span><span class="special">(</span> <span class="identifier">it</span> <span class="special">==</span> <span class="identifier">uset_object</span><span class="special">.</span><span class="identifier">end</span><span class="special">()</span> <span class="special">)</span> <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="keyword">return</span> <span class="special">&*</span><span class="identifier">it</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| <code class="computeroutput"><span class="identifier">Expensive</span></code> is an expensive |
| object to construct. If "key" c-string is quite long <code class="computeroutput"><span class="identifier">Expensive</span></code> has to construct a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code> |
| using heap memory. Like <code class="computeroutput"><span class="identifier">Expensive</span></code>, |
| many times the only member taking part in ordering issues is just a small |
| part of the class. For example, with <code class="computeroutput"><span class="identifier">Expensive</span></code>, |
| only the internal <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code> is needed to compare the object. |
| </p> |
| <p> |
| In both containers, if we call <code class="computeroutput"><span class="identifier">get_from_set</span><span class="special">/</span><span class="identifier">get_from_unordered_set</span></code> |
| in a loop, we might get a performance penalty, because we are forced to create |
| a whole <code class="computeroutput"><span class="identifier">Expensive</span></code> object |
| to be able to find an equivalent one. |
| </p> |
| <p> |
| Sometimes this interface limitation is severe, because we <span class="bold"><strong>might |
| not have enough information to construct the object</strong></span> but we might |
| <span class="bold"><strong>have enough information to find the object</strong></span>. |
| In this case, a name is enough to search <code class="computeroutput"><span class="identifier">Expensive</span></code> |
| in the container but constructing an <code class="computeroutput"><span class="identifier">Expensive</span></code> |
| might require more information that the user might not have. |
| </p> |
| <p> |
| To solve this, <code class="computeroutput"><a class="link" href="../boost/intrusive/set.html" title="Class template set">set</a></code>/<code class="computeroutput"><a class="link" href="../boost/intrusive/multiset.html" title="Class template multiset">multiset</a></code> offer alternative functions, |
| which take any type comparable with the value and a functor that should be |
| compatible with the ordering function of the associative container. <code class="computeroutput"><a class="link" href="../boost/intrusive/unordered_set.html" title="Class template unordered_set">unordered_set</a></code>/<code class="computeroutput"><a class="link" href="../boost/intrusive/unordered_multiset.html" title="Class template unordered_multiset">unordered_multiset</a></code> |
| offers functions that take any key type and compatible hash and equality |
| functions. Now, let's see the optimized search function: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="comment">// These compare Expensive and a c-string |
| </span><span class="keyword">struct</span> <span class="identifier">StrExpComp</span> |
| <span class="special">{</span> |
| <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">str</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">Expensive</span> <span class="special">&</span><span class="identifier">c</span><span class="special">)</span> <span class="keyword">const</span> |
| <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">strcmp</span><span class="special">(</span><span class="identifier">str</span><span class="special">,</span> <span class="identifier">c</span><span class="special">.</span><span class="identifier">get_key</span><span class="special">().</span><span class="identifier">c_str</span><span class="special">())</span> <span class="special"><</span> <span class="number">0</span><span class="special">;</span> <span class="special">}</span> |
| |
| <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="identifier">Expensive</span> <span class="special">&</span><span class="identifier">c</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">str</span><span class="special">)</span> <span class="keyword">const</span> |
| <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">strcmp</span><span class="special">(</span><span class="identifier">c</span><span class="special">.</span><span class="identifier">get_key</span><span class="special">().</span><span class="identifier">c_str</span><span class="special">(),</span> <span class="identifier">str</span><span class="special">)</span> <span class="special"><</span> <span class="number">0</span><span class="special">;</span> <span class="special">}</span> |
| <span class="special">};</span> |
| |
| <span class="keyword">struct</span> <span class="identifier">StrExpEqual</span> |
| <span class="special">{</span> |
| <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">str</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">Expensive</span> <span class="special">&</span><span class="identifier">c</span><span class="special">)</span> <span class="keyword">const</span> |
| <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">strcmp</span><span class="special">(</span><span class="identifier">str</span><span class="special">,</span> <span class="identifier">c</span><span class="special">.</span><span class="identifier">get_key</span><span class="special">().</span><span class="identifier">c_str</span><span class="special">())</span> <span class="special">==</span> <span class="number">0</span><span class="special">;</span> <span class="special">}</span> |
| |
| <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="identifier">Expensive</span> <span class="special">&</span><span class="identifier">c</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">str</span><span class="special">)</span> <span class="keyword">const</span> |
| <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">strcmp</span><span class="special">(</span><span class="identifier">c</span><span class="special">.</span><span class="identifier">get_key</span><span class="special">().</span><span class="identifier">c_str</span><span class="special">(),</span> <span class="identifier">str</span><span class="special">)</span> <span class="special">==</span> <span class="number">0</span><span class="special">;</span> <span class="special">}</span> |
| <span class="special">};</span> |
| |
| <span class="comment">// Optimized search functions |
| </span><span class="identifier">Expensive</span> <span class="special">*</span><span class="identifier">get_from_set_optimized</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">key</span><span class="special">,</span> <span class="identifier">Set</span> <span class="special">&</span><span class="identifier">set_object</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">Set</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">it</span> <span class="special">=</span> <span class="identifier">set_object</span><span class="special">.</span><span class="identifier">find</span><span class="special">(</span><span class="identifier">key</span><span class="special">,</span> <span class="identifier">StrExpComp</span><span class="special">());</span> |
| <span class="keyword">if</span><span class="special">(</span> <span class="identifier">it</span> <span class="special">==</span> <span class="identifier">set_object</span><span class="special">.</span><span class="identifier">end</span><span class="special">()</span> <span class="special">)</span> <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="keyword">return</span> <span class="special">&*</span><span class="identifier">it</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="identifier">Expensive</span> <span class="special">*</span><span class="identifier">get_from_uset_optimized</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">key</span><span class="special">,</span> <span class="identifier">UnorderedSet</span> <span class="special">&</span><span class="identifier">uset_object</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">UnorderedSet</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">it</span> <span class="special">=</span> <span class="identifier">uset_object</span><span class="special">.</span><span class="identifier">find</span><span class="special">(</span><span class="identifier">key</span><span class="special">,</span> <span class="identifier">StrHasher</span><span class="special">(),</span> <span class="identifier">StrExpEqual</span><span class="special">());</span> |
| <span class="keyword">if</span><span class="special">(</span> <span class="identifier">it</span> <span class="special">==</span> <span class="identifier">uset_object</span><span class="special">.</span><span class="identifier">end</span><span class="special">()</span> <span class="special">)</span> <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="keyword">return</span> <span class="special">&*</span><span class="identifier">it</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| This new arbitrary key overload is also available for other functions taking |
| values as arguments: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| equal_range |
| </li> |
| <li class="listitem"> |
| lower_bound |
| </li> |
| <li class="listitem"> |
| upper_bound |
| </li> |
| <li class="listitem"> |
| count |
| </li> |
| <li class="listitem"> |
| find |
| </li> |
| <li class="listitem"> |
| erase |
| </li> |
| </ul></div> |
| <p> |
| Check <code class="computeroutput"><a class="link" href="../boost/intrusive/set.html" title="Class template set">set</a></code>, <code class="computeroutput"><a class="link" href="../boost/intrusive/multiset.html" title="Class template multiset">multiset</a></code>, <code class="computeroutput"><a class="link" href="../boost/intrusive/unordered_set.html" title="Class template unordered_set">unordered_set</a></code>, |
| <code class="computeroutput"><a class="link" href="../boost/intrusive/unordered_multiset.html" title="Class template unordered_multiset">unordered_multiset</a></code> |
| references to know more about those functions. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="intrusive.advanced_lookups_insertions.advanced_insertions"></a><a class="link" href="advanced_lookups_insertions.html#intrusive.advanced_lookups_insertions.advanced_insertions" title="Advanced insertions">Advanced |
| insertions</a> |
| </h3></div></div></div> |
| <p> |
| A similar issue happens with insertions in simple ordered and unordered associative |
| containers with unique keys (<code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">set</span></code> and |
| <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">tr1</span><span class="special">::</span><span class="identifier">unordered_set</span></code>). |
| In these containers, if a value is already present, the value to be inserted |
| is discarded. With expensive values, if the value is already present, we |
| can suffer efficiency problems. |
| </p> |
| <p> |
| <code class="computeroutput"><a class="link" href="../boost/intrusive/set.html" title="Class template set">set</a></code> and <code class="computeroutput"><a class="link" href="../boost/intrusive/unordered_set.html" title="Class template unordered_set">unordered_set</a></code> |
| have insertion functions to check efficiently, without constructing the value, |
| if a value is present or not and if it's not present, a function to insert |
| it immediately without any further lookup. For example, using the same <code class="computeroutput"><span class="identifier">Expensive</span></code> class, this function can be inefficient: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="comment">// Insertion functions |
| </span><span class="keyword">bool</span> <span class="identifier">insert_to_set</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">key</span><span class="special">,</span> <span class="identifier">Set</span> <span class="special">&</span><span class="identifier">set_object</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">Expensive</span> <span class="special">*</span><span class="identifier">pobject</span> <span class="special">=</span> <span class="keyword">new</span> <span class="identifier">Expensive</span><span class="special">(</span><span class="identifier">key</span><span class="special">);</span> |
| <span class="keyword">bool</span> <span class="identifier">success</span> <span class="special">=</span> <span class="identifier">set_object</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(*</span><span class="identifier">pobject</span><span class="special">).</span><span class="identifier">second</span><span class="special">;</span> |
| <span class="keyword">if</span><span class="special">(!</span><span class="identifier">success</span><span class="special">)</span> <span class="keyword">delete</span> <span class="identifier">pobject</span><span class="special">;</span> |
| <span class="keyword">return</span> <span class="identifier">success</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">bool</span> <span class="identifier">insert_to_uset</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">key</span><span class="special">,</span> <span class="identifier">UnorderedSet</span> <span class="special">&</span><span class="identifier">uset_object</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">Expensive</span> <span class="special">*</span><span class="identifier">pobject</span> <span class="special">=</span> <span class="keyword">new</span> <span class="identifier">Expensive</span><span class="special">(</span><span class="identifier">key</span><span class="special">);</span> |
| <span class="keyword">bool</span> <span class="identifier">success</span> <span class="special">=</span> <span class="identifier">uset_object</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(*</span><span class="identifier">pobject</span><span class="special">).</span><span class="identifier">second</span><span class="special">;</span> |
| <span class="keyword">if</span><span class="special">(!</span><span class="identifier">success</span><span class="special">)</span> <span class="keyword">delete</span> <span class="identifier">pobject</span><span class="special">;</span> |
| <span class="keyword">return</span> <span class="identifier">success</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| If the object is already present, we are constructing an <code class="computeroutput"><span class="identifier">Expensive</span></code> |
| that will be discarded, and this is a waste of resources. Instead of that, |
| let's use <code class="computeroutput"><span class="identifier">insert_check</span></code> and |
| <code class="computeroutput"><span class="identifier">insert_commit</span></code> functions: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="comment">// Optimized insertion functions |
| </span><span class="keyword">bool</span> <span class="identifier">insert_to_set_optimized</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">key</span><span class="special">,</span> <span class="identifier">Set</span> <span class="special">&</span><span class="identifier">set_object</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">Set</span><span class="special">::</span><span class="identifier">insert_commit_data</span> <span class="identifier">insert_data</span><span class="special">;</span> |
| <span class="keyword">bool</span> <span class="identifier">success</span> <span class="special">=</span> <span class="identifier">set_object</span><span class="special">.</span><span class="identifier">insert_check</span><span class="special">(</span><span class="identifier">key</span><span class="special">,</span> <span class="identifier">StrExpComp</span><span class="special">(),</span> <span class="identifier">insert_data</span><span class="special">).</span><span class="identifier">second</span><span class="special">;</span> |
| <span class="keyword">if</span><span class="special">(</span><span class="identifier">success</span><span class="special">)</span> <span class="identifier">set_object</span><span class="special">.</span><span class="identifier">insert_commit</span><span class="special">(*</span><span class="keyword">new</span> <span class="identifier">Expensive</span><span class="special">(</span><span class="identifier">key</span><span class="special">),</span> <span class="identifier">insert_data</span><span class="special">);</span> |
| <span class="keyword">return</span> <span class="identifier">success</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">bool</span> <span class="identifier">insert_to_uset_optimized</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">key</span><span class="special">,</span> <span class="identifier">UnorderedSet</span> <span class="special">&</span><span class="identifier">uset_object</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">UnorderedSet</span><span class="special">::</span><span class="identifier">insert_commit_data</span> <span class="identifier">insert_data</span><span class="special">;</span> |
| <span class="keyword">bool</span> <span class="identifier">success</span> <span class="special">=</span> <span class="identifier">uset_object</span><span class="special">.</span><span class="identifier">insert_check</span> |
| <span class="special">(</span><span class="identifier">key</span><span class="special">,</span> <span class="identifier">StrHasher</span><span class="special">(),</span> <span class="identifier">StrExpEqual</span><span class="special">(),</span> <span class="identifier">insert_data</span><span class="special">).</span><span class="identifier">second</span><span class="special">;</span> |
| <span class="keyword">if</span><span class="special">(</span><span class="identifier">success</span><span class="special">)</span> <span class="identifier">uset_object</span><span class="special">.</span><span class="identifier">insert_commit</span><span class="special">(*</span><span class="keyword">new</span> <span class="identifier">Expensive</span><span class="special">(</span><span class="identifier">key</span><span class="special">),</span> <span class="identifier">insert_data</span><span class="special">);</span> |
| <span class="keyword">return</span> <span class="identifier">success</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| <code class="computeroutput"><span class="identifier">insert_check</span></code> is similar to |
| a normal <code class="computeroutput"><span class="identifier">insert</span></code> but: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| <code class="computeroutput"><span class="identifier">insert_check</span></code> can be used |
| with arbitrary keys |
| </li> |
| <li class="listitem"> |
| <p class="simpara"> |
| if the insertion is possible (there is no equivalent value) <code class="computeroutput"><span class="identifier">insert_check</span></code> collects all the needed |
| information in an <code class="computeroutput"><span class="identifier">insert_commit_data</span></code> |
| structure, so that <code class="computeroutput"><span class="identifier">insert_commit</span></code>: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="circle"> |
| <li class="listitem"> |
| <span class="bold"><strong>does not execute</strong></span> further comparisons |
| </li> |
| <li class="listitem"> |
| can be executed with <span class="bold"><strong>constant-time complexity</strong></span> |
| </li> |
| <li class="listitem"> |
| has <span class="bold"><strong>no-throw guarantee</strong></span>. |
| </li> |
| </ul></div> |
| </li> |
| </ul></div> |
| <p> |
| These functions must be used with care, since no other insertion or erasure |
| must be executed between an <code class="computeroutput"><span class="identifier">insert_check</span></code> |
| and an <code class="computeroutput"><span class="identifier">insert_commit</span></code> pair. |
| Otherwise, the behaviour is undefined. <code class="computeroutput"><span class="identifier">insert_check</span></code> |
| and <code class="computeroutput"><span class="identifier">insert_commit</span></code> will come |
| in handy for developers programming efficient non-intrusive associative containers. |
| See <code class="computeroutput"><a class="link" href="../boost/intrusive/set.html" title="Class template set">set</a></code> and <code class="computeroutput"><a class="link" href="../boost/intrusive/unordered_set.html" title="Class template unordered_set">unordered_set</a></code> reference |
| for more information about <code class="computeroutput"><span class="identifier">insert_check</span></code> |
| and <code class="computeroutput"><span class="identifier">insert_commit</span></code>. |
| </p> |
| <p> |
| With multiple ordered and unordered associative containers (<code class="computeroutput"><a class="link" href="../boost/intrusive/multiset.html" title="Class template multiset">multiset</a></code> |
| and <code class="computeroutput"><a class="link" href="../boost/intrusive/unordered_multiset.html" title="Class template unordered_multiset">unordered_multiset</a></code>) |
| there is no need for these advanced insertion functions, since insertions |
| are always successful. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="intrusive.advanced_lookups_insertions.positional_insertions"></a><a class="link" href="advanced_lookups_insertions.html#intrusive.advanced_lookups_insertions.positional_insertions" title="Positional insertions">Positional |
| insertions</a> |
| </h3></div></div></div> |
| <p> |
| Some ordered associative containers offer low-level functions to bypass ordering |
| checks and insert nodes directly in desired tree positions. These functions |
| are provided for performance reasons when values to be inserted in the container |
| are known to fulfill order (sets and multisets) and uniqueness (sets) invariants. |
| A typical usage of these functions is when intrusive associative containers |
| are used to build non-intrusive containers and the programmer wants to speed |
| up assignments from other associative containers: if the ordering and uniqueness |
| properties are the same, there is no need to waste time checking the position |
| of each source value, because values are already ordered: back insertions |
| will be much more efficient. |
| </p> |
| <p> |
| <span class="bold"><strong>Note:</strong></span> These functions <span class="bold"><strong>don't |
| check preconditions</strong></span> so they must used with care. These are functions |
| are low-level operations <span class="bold"><strong>will break container invariants |
| if ordering and uniqueness preconditions are not assured by the caller.</strong></span> |
| </p> |
| <p> |
| Let's see an example: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">intrusive</span><span class="special">/</span><span class="identifier">set</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">vector</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">algorithm</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> |
| |
| <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">intrusive</span><span class="special">;</span> |
| |
| <span class="comment">//A simple class with a set hook |
| </span><span class="keyword">class</span> <span class="identifier">MyClass</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">set_base_hook</span><span class="special"><></span> |
| <span class="special">{</span> |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="keyword">int</span> <span class="identifier">int_</span><span class="special">;</span> |
| |
| <span class="identifier">MyClass</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">int_</span><span class="special">(</span><span class="identifier">i</span><span class="special">)</span> <span class="special">{}</span> |
| <span class="keyword">friend</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special"><</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">MyClass</span> <span class="special">&</span><span class="identifier">a</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">MyClass</span> <span class="special">&</span><span class="identifier">b</span><span class="special">)</span> |
| <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">a</span><span class="special">.</span><span class="identifier">int_</span> <span class="special"><</span> <span class="identifier">b</span><span class="special">.</span><span class="identifier">int_</span><span class="special">;</span> <span class="special">}</span> |
| <span class="keyword">friend</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">></span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">MyClass</span> <span class="special">&</span><span class="identifier">a</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">MyClass</span> <span class="special">&</span><span class="identifier">b</span><span class="special">)</span> |
| <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">a</span><span class="special">.</span><span class="identifier">int_</span> <span class="special">></span> <span class="identifier">b</span><span class="special">.</span><span class="identifier">int_</span><span class="special">;</span> <span class="special">}</span> |
| <span class="special">};</span> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="comment">//Create some ORDERED elements |
| </span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">></span> <span class="identifier">values</span><span class="special">;</span> |
| <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="number">100</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="identifier">values</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">MyClass</span><span class="special">(</span><span class="identifier">i</span><span class="special">));</span> |
| |
| <span class="special">{</span> <span class="comment">//Data is naturally ordered in the vector with the same criteria |
| </span> <span class="comment">//as multiset's comparison predicate, so we can just push back |
| </span> <span class="comment">//all elements, which is more efficient than normal insertion |
| </span> <span class="identifier">multiset</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">></span> <span class="identifier">mset</span><span class="special">;</span> |
| <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="number">100</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="identifier">mset</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">values</span><span class="special">[</span><span class="identifier">i</span><span class="special">]);</span> |
| |
| <span class="comment">//Now check orderd invariant |
| </span> <span class="identifier">multiset</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">>::</span><span class="identifier">const_iterator</span> <span class="identifier">next</span><span class="special">(</span><span class="identifier">mset</span><span class="special">.</span><span class="identifier">cbegin</span><span class="special">()),</span> <span class="identifier">it</span><span class="special">(</span><span class="identifier">next</span><span class="special">++);</span> |
| <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="number">99</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">,</span> <span class="special">++</span><span class="identifier">it</span><span class="special">,</span> <span class="special">++</span><span class="identifier">next</span><span class="special">)</span> <span class="identifier">assert</span><span class="special">(*</span><span class="identifier">it</span> <span class="special"><</span> <span class="special">*</span><span class="identifier">next</span><span class="special">);</span> |
| <span class="special">}</span> |
| <span class="special">{</span> <span class="comment">//Now the correct order for the set is the reverse order |
| </span> <span class="comment">//so let's push front all elements |
| </span> <span class="identifier">multiset</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">,</span> <span class="identifier">compare</span><span class="special"><</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">greater</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">></span> <span class="special">></span> <span class="special">></span> <span class="identifier">mset</span><span class="special">;</span> |
| <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="number">100</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="identifier">mset</span><span class="special">.</span><span class="identifier">push_front</span><span class="special">(</span><span class="identifier">values</span><span class="special">[</span><span class="identifier">i</span><span class="special">]);</span> |
| |
| <span class="comment">//Now check orderd invariant |
| </span> <span class="identifier">multiset</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">,</span> <span class="identifier">compare</span><span class="special"><</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">greater</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">></span> <span class="special">></span> <span class="special">>::</span> |
| <span class="identifier">const_iterator</span> <span class="identifier">next</span><span class="special">(</span><span class="identifier">mset</span><span class="special">.</span><span class="identifier">cbegin</span><span class="special">()),</span> <span class="identifier">it</span><span class="special">(</span><span class="identifier">next</span><span class="special">++);</span> |
| <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="number">99</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">,</span> <span class="special">++</span><span class="identifier">it</span><span class="special">,</span> <span class="special">++</span><span class="identifier">next</span><span class="special">)</span> <span class="identifier">assert</span><span class="special">(*</span><span class="identifier">it</span> <span class="special">></span> <span class="special">*</span><span class="identifier">next</span><span class="special">);</span> |
| <span class="special">}</span> |
| <span class="special">{</span> <span class="comment">//Now push the first and the last and insert the rest |
| </span> <span class="comment">//before the last position using "insert_before" |
| </span> <span class="identifier">multiset</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">></span> <span class="identifier">mset</span><span class="special">;</span> |
| <span class="identifier">mset</span><span class="special">.</span><span class="identifier">insert_before</span><span class="special">(</span><span class="identifier">mset</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">values</span><span class="special">[</span><span class="number">0</span><span class="special">]);</span> |
| <span class="identifier">multiset</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">>::</span><span class="identifier">const_iterator</span> <span class="identifier">pos</span> <span class="special">=</span> |
| <span class="identifier">mset</span><span class="special">.</span><span class="identifier">insert_before</span><span class="special">(</span><span class="identifier">mset</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">values</span><span class="special">[</span><span class="number">99</span><span class="special">]);</span> |
| <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="number">99</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="identifier">mset</span><span class="special">.</span><span class="identifier">insert_before</span><span class="special">(</span><span class="identifier">pos</span><span class="special">,</span> <span class="identifier">values</span><span class="special">[</span><span class="identifier">i</span><span class="special">]);</span> |
| |
| <span class="comment">//Now check orderd invariant |
| </span> <span class="identifier">multiset</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">>::</span><span class="identifier">const_iterator</span> <span class="identifier">next</span><span class="special">(</span><span class="identifier">mset</span><span class="special">.</span><span class="identifier">cbegin</span><span class="special">()),</span> <span class="identifier">it</span><span class="special">(</span><span class="identifier">next</span><span class="special">++);</span> |
| <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="number">99</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">,</span> <span class="special">++</span><span class="identifier">it</span><span class="special">,</span> <span class="special">++</span><span class="identifier">next</span><span class="special">)</span> <span class="identifier">assert</span><span class="special">(*</span><span class="identifier">it</span> <span class="special"><</span> <span class="special">*</span><span class="identifier">next</span><span class="special">);</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
| <p> |
| For more information about advanced lookup and insertion functions see associative |
| containers' documentation (e.g. <code class="computeroutput"><a class="link" href="../boost/intrusive/set.html" title="Class template set">set</a></code>, |
| <code class="computeroutput"><a class="link" href="../boost/intrusive/multiset.html" title="Class template multiset">multiset</a></code>, <code class="computeroutput"><a class="link" href="../boost/intrusive/unordered_set.html" title="Class template unordered_set">unordered_set</a></code> and <code class="computeroutput"><a class="link" href="../boost/intrusive/unordered_multiset.html" title="Class template unordered_multiset">unordered_multiset</a></code> references). |
| </p> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2005 Olaf Krzikalla, 2006-2010 Ion Gaztanaga<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| 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>) |
| </p> |
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