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| <div class="section"> |
| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="log.detailed"></a><a class="link" href="detailed.html" title="Detailed features description">Detailed features description</a> |
| </h2></div></div></div> |
| <div class="toc"><dl class="toc"> |
| <dt><span class="section"><a href="detailed.html#log.detailed.core">Core facilities</a></span></dt> |
| <dt><span class="section"><a href="detailed/sources.html">Logging sources</a></span></dt> |
| <dt><span class="section"><a href="detailed/sink_frontends.html">Sink frontends</a></span></dt> |
| <dt><span class="section"><a href="detailed/sink_backends.html">Sink backends</a></span></dt> |
| <dt><span class="section"><a href="detailed/expressions.html">Lambda expressions</a></span></dt> |
| <dt><span class="section"><a href="detailed/attributes.html">Attributes</a></span></dt> |
| <dt><span class="section"><a href="detailed/utilities.html">Utilities</a></span></dt> |
| </dl></div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="log.detailed.core"></a><a class="link" href="detailed.html#log.detailed.core" title="Core facilities">Core facilities</a> |
| </h3></div></div></div> |
| <div class="toc"><dl class="toc"> |
| <dt><span class="section"><a href="detailed.html#log.detailed.core.record">Logging records</a></span></dt> |
| <dt><span class="section"><a href="detailed.html#log.detailed.core.core">Logging core</a></span></dt> |
| </dl></div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="log.detailed.core.record"></a><a class="link" href="detailed.html#log.detailed.core.record" title="Logging records">Logging records</a> |
| </h4></div></div></div> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><code class="computeroutput"><a class="link" href="../core_components.html#header.boost.log.core.record_hpp" title="Header <boost/log/core/record.hpp>">boost/log/core/record.hpp</a></code><span class="special">></span> |
| </pre> |
| <p> |
| All the information that the logging library processes is packed into a |
| single object of type <code class="computeroutput"><a class="link" href="../boost/log/record.html" title="Class record">record</a></code>. |
| All attached data, including the message text, is represented as named |
| attribute values that can be fetched and processed by filters, formatters |
| and sinks. Particular attribute values can be accessed in different ways, |
| here are a few quick examples: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| Through <a class="link" href="detailed/attributes.html#log.detailed.attributes.related_components.value_processing" title="Attribute value extraction and visitation">value |
| visitation and extraction</a>. |
| </li></ul></div> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">enum</span> <span class="identifier">severity_level</span> <span class="special">{</span> <span class="special">...</span> <span class="special">};</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">ostream</span><span class="special">&</span> <span class="keyword">operator</span><span class="special"><<</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">ostream</span><span class="special">&</span> <span class="identifier">strm</span><span class="special">,</span> <span class="identifier">severity_level</span> <span class="identifier">level</span><span class="special">);</span> |
| |
| <span class="keyword">struct</span> <span class="identifier">print_visitor</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="keyword">void</span> <span class="identifier">result_type</span><span class="special">;</span> |
| <span class="identifier">result_type</span> <span class="keyword">operator</span><span class="special">()</span> <span class="special">(</span><span class="identifier">severity_level</span> <span class="identifier">level</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">cout</span> <span class="special"><<</span> <span class="identifier">level</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="special">};</span> |
| <span class="special">};</span> |
| |
| <span class="comment">// Prints severity level through visitation API</span> |
| <span class="keyword">void</span> <span class="identifier">print_severity_visitation</span><span class="special">(</span><span class="identifier">logging</span><span class="special">::</span><span class="identifier">record</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rec</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">logging</span><span class="special">::</span><span class="identifier">visit</span><span class="special"><</span> <span class="identifier">severity_level</span> <span class="special">>(</span><span class="string">"Severity"</span><span class="special">,</span> <span class="identifier">rec</span><span class="special">,</span> <span class="identifier">print_visitor</span><span class="special">());</span> |
| <span class="special">}</span> |
| |
| <span class="comment">// Prints severity level through extraction API</span> |
| <span class="keyword">void</span> <span class="identifier">print_severity_extraction</span><span class="special">(</span><span class="identifier">logging</span><span class="special">::</span><span class="identifier">record</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rec</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">logging</span><span class="special">::</span><span class="identifier">value_ref</span><span class="special"><</span> <span class="identifier">severity_level</span> <span class="special">></span> <span class="identifier">level</span> <span class="special">=</span> <span class="identifier">logging</span><span class="special">::</span><span class="identifier">extract</span><span class="special"><</span> <span class="identifier">severity_level</span> <span class="special">>(</span><span class="string">"Severity"</span><span class="special">,</span> <span class="identifier">rec</span><span class="special">);</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">level</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| By searching the <a class="link" href="detailed/attributes.html#log.detailed.attributes.related_components.attribute_value_set" title="Attribute value set">set |
| of attribute values</a> accessible with the <code class="computeroutput"><span class="identifier">attribute_values</span></code> |
| method of the record. |
| </li></ul></div> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="comment">// Prints severity level by searching the attribute values</span> |
| <span class="keyword">void</span> <span class="identifier">print_severity_lookup</span><span class="special">(</span><span class="identifier">logging</span><span class="special">::</span><span class="identifier">record</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rec</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">logging</span><span class="special">::</span><span class="identifier">attribute_value_set</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">values</span> <span class="special">=</span> <span class="identifier">rec</span><span class="special">.</span><span class="identifier">attribute_values</span><span class="special">();</span> |
| <span class="identifier">logging</span><span class="special">::</span><span class="identifier">attribute_value_set</span><span class="special">::</span><span class="identifier">const_iterator</span> <span class="identifier">it</span> <span class="special">=</span> <span class="identifier">values</span><span class="special">.</span><span class="identifier">find</span><span class="special">(</span><span class="string">"Severity"</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">values</span><span class="special">.</span><span class="identifier">end</span><span class="special">())</span> |
| <span class="special">{</span> |
| <span class="identifier">logging</span><span class="special">::</span><span class="identifier">attribute_value</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">value</span> <span class="special">=</span> <span class="identifier">it</span><span class="special">-></span><span class="identifier">second</span><span class="special">;</span> |
| |
| <span class="comment">// A single attribute value can also be visited or extracted</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">value</span><span class="special">.</span><span class="identifier">extract</span><span class="special"><</span> <span class="identifier">severity_level</span> <span class="special">>()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> |
| By applying the subscript operator with the attribute keyword. This |
| is actually a convenience wrapper around the value extraction API. |
| </li></ul></div> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="identifier">BOOST_LOG_ATTRIBUTE_KEYWORD</span><span class="special">(</span><span class="identifier">severity</span><span class="special">,</span> <span class="string">"Severity"</span><span class="special">,</span> <span class="identifier">severity_level</span><span class="special">)</span> |
| |
| <span class="comment">// Prints severity level by using the subscript operator</span> |
| <span class="keyword">void</span> <span class="identifier">print_severity_subscript</span><span class="special">(</span><span class="identifier">logging</span><span class="special">::</span><span class="identifier">record</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rec</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="comment">// Use the attribute keyword to communicate the name and type of the value</span> |
| <span class="identifier">logging</span><span class="special">::</span><span class="identifier">value_ref</span><span class="special"><</span> <span class="identifier">severity_level</span><span class="special">,</span> <span class="identifier">tag</span><span class="special">::</span><span class="identifier">severity</span> <span class="special">></span> <span class="identifier">level</span> <span class="special">=</span> <span class="identifier">rec</span><span class="special">[</span><span class="identifier">severity</span><span class="special">];</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">level</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Log records cannot be copied, only moved. A record can be default-constructed |
| in which case it is in an empty state; such records are mostly unusable |
| and should not be passed to the library for processing. Non-empty log records |
| can only be created by the <a class="link" href="detailed.html#log.detailed.core.core" title="Logging core">logging |
| core</a> as a result of successful filtering. The non-empty record contains |
| attribute values acquired from attributes. More attribute values can be |
| added to the non-empty record after filtering. The added values will not |
| affect filtering results but can still be used by formatters and sinks. |
| </p> |
| <p> |
| In multithreaded environments, after being constructed a non-empty log |
| record is considered to be tied to the current thread as it may refer to |
| some thread-specific resources. For example, the record may contain an |
| attribute value which refers to the named scope list which is stored on |
| the stack. For this reason log records must not be passed between different |
| threads. |
| </p> |
| <h6> |
| <a name="log.detailed.core.record.h0"></a> |
| <span class="phrase"><a name="log.detailed.core.record.record_views"></a></span><a class="link" href="detailed.html#log.detailed.core.record.record_views">Record |
| views</a> |
| </h6> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><code class="computeroutput"><a class="link" href="../core_components.html#header.boost.log.core.record_view_hpp" title="Header <boost/log/core/record_view.hpp>">boost/log/core/record_view.hpp</a></code><span class="special">></span> |
| </pre> |
| <p> |
| While records are used for filling the information, the library uses another |
| type to actually process it. Record views provide a similar interface to |
| records with a few notable distinctions: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> |
| <li class="listitem"> |
| Record views are immutable. This prevents formatters and sinks from |
| modifying the record while it is being processed. |
| </li> |
| <li class="listitem"> |
| Record views are copyable. Since its contents are constant, the copy |
| operation is shallow and therefore cheap. |
| </li> |
| </ul></div> |
| <p> |
| The library will automatically create a record view from the record by |
| calling the <code class="computeroutput"><span class="identifier">lock</span></code> method. |
| The call will also make sure the resulting view is not attached to the |
| current thread if a sink is asynchronous. The <code class="computeroutput"><span class="identifier">lock</span></code> |
| call is a one time operation; the record is left in the empty state afterwards. |
| All APIs for interacting with attribute values described for log records |
| are also applicable to record views and can be used in custom formatters |
| and sinks. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="log.detailed.core.core"></a><a class="link" href="detailed.html#log.detailed.core.core" title="Logging core">Logging core</a> |
| </h4></div></div></div> |
| <div class="toc"><dl class="toc"> |
| <dt><span class="section"><a href="detailed.html#log.detailed.core.core.attribute_sets">Attribute |
| sets</a></span></dt> |
| <dt><span class="section"><a href="detailed.html#log.detailed.core.core.filtering">Global filtering</a></span></dt> |
| <dt><span class="section"><a href="detailed.html#log.detailed.core.core.sinks">Sink management</a></span></dt> |
| <dt><span class="section"><a href="detailed.html#log.detailed.core.core.exception_handling">Exception |
| handling</a></span></dt> |
| <dt><span class="section"><a href="detailed.html#log.detailed.core.core.record_feeding">Feeding log |
| records</a></span></dt> |
| </dl></div> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><code class="computeroutput"><a class="link" href="../core_components.html#header.boost.log.core.core_hpp" title="Header <boost/log/core/core.hpp>">boost/log/core/core.hpp</a></code><span class="special">></span> |
| </pre> |
| <p> |
| The logging core is a central hub that provides the following facilities: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> |
| <li class="listitem"> |
| Maintains global and thread-specific attribute sets. |
| </li> |
| <li class="listitem"> |
| Performs global filtering of log records. |
| </li> |
| <li class="listitem"> |
| Dispatches log records between sinks by applying sink-specific filters. |
| </li> |
| <li class="listitem"> |
| Provides a global hook for exception handlers. |
| </li> |
| <li class="listitem"> |
| Provides an entry point for log sources to put log records to. |
| </li> |
| <li class="listitem"> |
| Provides the <code class="computeroutput"><span class="identifier">flush</span></code> |
| method that can be used to enforce the synchronized state for all log |
| sinks. |
| </li> |
| </ul></div> |
| <p> |
| The logging core is an application-wide singleton, thus every logging source |
| has access to it. The core instance is accessible with the static method |
| <code class="computeroutput"><span class="identifier">get</span></code>. |
| </p> |
| <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span><span class="special"><</span> <span class="identifier">logging</span><span class="special">::</span><span class="identifier">core</span> <span class="special">></span> <span class="identifier">core</span> <span class="special">=</span> <span class="identifier">logging</span><span class="special">::</span><span class="identifier">core</span><span class="special">::</span><span class="identifier">get</span><span class="special">();</span> |
| |
| <span class="comment">// ...</span> |
| <span class="special">}</span> |
| </pre> |
| <div class="section"> |
| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="log.detailed.core.core.attribute_sets"></a><a class="link" href="detailed.html#log.detailed.core.core.attribute_sets" title="Attribute sets">Attribute |
| sets</a> |
| </h5></div></div></div> |
| <p> |
| In order to add or remove global or thread-specific attributes to the |
| core there are corresponding methods: <code class="computeroutput"><span class="identifier">add_global_attribute</span></code>, |
| <code class="computeroutput"><span class="identifier">remove_global_attribute</span></code>, |
| <code class="computeroutput"><span class="identifier">add_thread_attribute</span></code> |
| and <code class="computeroutput"><span class="identifier">remove_thread_attribute</span></code>. |
| Attribute sets provide interface similar to <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span></code>, |
| so the <code class="computeroutput"><span class="identifier">add_</span><span class="special">*</span></code> |
| methods accept an attribute name string (key) and a pointer to the attribute |
| (mapped value) and return a pair of iterator and boolean value, like |
| <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span> <span class="special">...</span> <span class="special">>::</span><span class="identifier">insert</span></code> does. The <code class="computeroutput"><span class="identifier">remove_</span><span class="special">*</span></code> methods accept an iterator to a previously |
| added attribute. |
| </p> |
| <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span><span class="special"><</span> <span class="identifier">logging</span><span class="special">::</span><span class="identifier">core</span> <span class="special">></span> <span class="identifier">core</span> <span class="special">=</span> <span class="identifier">logging</span><span class="special">::</span><span class="identifier">core</span><span class="special">::</span><span class="identifier">get</span><span class="special">();</span> |
| |
| <span class="comment">// Add a global attribute</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span> <span class="identifier">logging</span><span class="special">::</span><span class="identifier">attribute_set</span><span class="special">::</span><span class="identifier">iterator</span><span class="special">,</span> <span class="keyword">bool</span> <span class="special">></span> <span class="identifier">res</span> <span class="special">=</span> |
| <span class="identifier">core</span><span class="special">-></span><span class="identifier">add_global_attribute</span><span class="special">(</span><span class="string">"LineID"</span><span class="special">,</span> <span class="identifier">attrs</span><span class="special">::</span><span class="identifier">counter</span><span class="special"><</span> <span class="keyword">unsigned</span> <span class="keyword">int</span> <span class="special">>());</span> |
| |
| <span class="comment">// ...</span> |
| |
| <span class="comment">// Remove the added attribute</span> |
| <span class="identifier">core</span><span class="special">-></span><span class="identifier">remove_global_attribute</span><span class="special">(</span><span class="identifier">res</span><span class="special">.</span><span class="identifier">first</span><span class="special">);</span> |
| <span class="special">}</span> |
| </pre> |
| <div class="tip"><table border="0" summary="Tip"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../../doc/src/images/tip.png"></td> |
| <th align="left">Tip</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| It must be said that all methods of logging core are thread-safe in |
| multithreaded environments. However, that may not be true for other |
| components, such as iterators or attribute sets. |
| </p></td></tr> |
| </table></div> |
| <p> |
| It is possible to acquire a copy of the whole attribute set (global or |
| thread-specific) or install it into the core. Methods <code class="computeroutput"><span class="identifier">get_global_attributes</span></code>, |
| <code class="computeroutput"><span class="identifier">set_global_attributes</span></code>, |
| <code class="computeroutput"><span class="identifier">get_thread_attributes</span></code> |
| and <code class="computeroutput"><span class="identifier">set_thread_attributes</span></code> |
| serve this purpose. |
| </p> |
| <div class="warning"><table border="0" summary="Warning"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../../doc/src/images/warning.png"></td> |
| <th align="left">Warning</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| After installing a whole attribute set into the core, all iterators |
| that were previously returned by the corresponding <code class="computeroutput"><span class="identifier">add_</span><span class="special">*</span></code> methods are invalidated. In particular, |
| it affects <a class="link" href="detailed/attributes.html#log.detailed.attributes.related_components.scoped_attributes" title="Scoped attributes">scoped |
| attributes</a>, so the user must be careful when to switch attribute |
| sets. |
| </p></td></tr> |
| </table></div> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="log.detailed.core.core.filtering"></a><a class="link" href="detailed.html#log.detailed.core.core.filtering" title="Global filtering">Global filtering</a> |
| </h5></div></div></div> |
| <p> |
| Global filtering is handled by the filter function object, which can |
| be provided with the <code class="computeroutput"><span class="identifier">set_filter</span></code> |
| method. More on creating filters appears in <a class="link" href="detailed/expressions.html#log.detailed.expressions.predicates" title="Predicate expressions">this |
| section</a>. Here it will suffice to say that the filter accepts a |
| set of attribute values and returns a boolean value that tells whether |
| a log record with these attribute values passed filtering or not. The |
| global filter is applied to every log record made throughout the application, |
| so it can be used to wipe out excessive log records quickly. |
| </p> |
| <p> |
| The global filter can be removed by the <code class="computeroutput"><span class="identifier">reset_filter</span></code> |
| method. When there is no filter set in the core it is assumed that no |
| records are filtered away. This is the default after initial construction |
| of the logging core. |
| </p> |
| <pre class="programlisting"><span class="keyword">enum</span> <span class="identifier">severity_level</span> |
| <span class="special">{</span> |
| <span class="identifier">normal</span><span class="special">,</span> |
| <span class="identifier">warning</span><span class="special">,</span> |
| <span class="identifier">error</span><span class="special">,</span> |
| <span class="identifier">critical</span> |
| <span class="special">};</span> |
| |
| <span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span><span class="special"><</span> <span class="identifier">logging</span><span class="special">::</span><span class="identifier">core</span> <span class="special">></span> <span class="identifier">core</span> <span class="special">=</span> <span class="identifier">logging</span><span class="special">::</span><span class="identifier">core</span><span class="special">::</span><span class="identifier">get</span><span class="special">();</span> |
| |
| <span class="comment">// Set a global filter so that only error messages are logged</span> |
| <span class="identifier">core</span><span class="special">-></span><span class="identifier">set_filter</span><span class="special">(</span><span class="identifier">expr</span><span class="special">::</span><span class="identifier">attr</span><span class="special"><</span> <span class="identifier">severity_level</span> <span class="special">>(</span><span class="string">"Severity"</span><span class="special">)</span> <span class="special">>=</span> <span class="identifier">error</span><span class="special">);</span> |
| |
| <span class="comment">// ...</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| The core also provides another way to disable logging. By calling the |
| <code class="computeroutput"><span class="identifier">set_logging_enabled</span></code> with |
| a boolean argument one may completely disable or re-enable logging, including |
| applying filtering. Disabling logging with this method may be more beneficial |
| in terms of application performance than setting a global filter that |
| always fails. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="log.detailed.core.core.sinks"></a><a class="link" href="detailed.html#log.detailed.core.core.sinks" title="Sink management">Sink management</a> |
| </h5></div></div></div> |
| <p> |
| After global filtering is applied, log sinks step into action. In order |
| to add and remove sinks the core provides <code class="computeroutput"><span class="identifier">add_sink</span></code> |
| and <code class="computeroutput"><span class="identifier">remove_sink</span></code> methods. |
| Both these methods accept a pointer to the sink. The <code class="computeroutput"><span class="identifier">add_sink</span></code> |
| will add the sink to the core if it's not added already. The <code class="computeroutput"><span class="identifier">remove_sink</span></code> method will seek for the |
| provided sink in an internal list of previously added sinks and remove |
| the sink if it finds it. The order in which the core processes sinks |
| internally is unspecified. |
| </p> |
| <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span><span class="special"><</span> <span class="identifier">logging</span><span class="special">::</span><span class="identifier">core</span> <span class="special">></span> <span class="identifier">core</span> <span class="special">=</span> <span class="identifier">logging</span><span class="special">::</span><span class="identifier">core</span><span class="special">::</span><span class="identifier">get</span><span class="special">();</span> |
| |
| <span class="comment">// Set a sink that will write log records to the console</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span><span class="special"><</span> <span class="identifier">sinks</span><span class="special">::</span><span class="identifier">text_ostream_backend</span> <span class="special">></span> <span class="identifier">backend</span> <span class="special">=</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_shared</span><span class="special"><</span> <span class="identifier">sinks</span><span class="special">::</span><span class="identifier">text_ostream_backend</span> <span class="special">>();</span> |
| <span class="identifier">backend</span><span class="special">-></span><span class="identifier">add_stream</span><span class="special">(</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span><span class="special"><</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">ostream</span> <span class="special">>(&</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">clog</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">null_deleter</span><span class="special">()));</span> |
| |
| <span class="keyword">typedef</span> <span class="identifier">sinks</span><span class="special">::</span><span class="identifier">unlocked_sink</span><span class="special"><</span> <span class="identifier">sinks</span><span class="special">::</span><span class="identifier">text_ostream_backend</span> <span class="special">></span> <span class="identifier">sink_t</span><span class="special">;</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span><span class="special"><</span> <span class="identifier">sink_t</span> <span class="special">></span> <span class="identifier">sink</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_shared</span><span class="special"><</span> <span class="identifier">sink_t</span> <span class="special">>(</span><span class="identifier">backend</span><span class="special">);</span> |
| <span class="identifier">core</span><span class="special">-></span><span class="identifier">add_sink</span><span class="special">(</span><span class="identifier">sink</span><span class="special">);</span> |
| |
| <span class="comment">// ...</span> |
| |
| <span class="comment">// Remove the sink</span> |
| <span class="identifier">core</span><span class="special">-></span><span class="identifier">remove_sink</span><span class="special">(</span><span class="identifier">sink</span><span class="special">);</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| You can read more on the design of sinks in the following sections: |
| <a class="link" href="detailed/sink_frontends.html" title="Sink frontends">Sink Frontends</a> and |
| <a class="link" href="detailed/sink_backends.html" title="Sink backends">Sink Backends</a>. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="log.detailed.core.core.exception_handling"></a><a class="link" href="detailed.html#log.detailed.core.core.exception_handling" title="Exception handling">Exception |
| handling</a> |
| </h5></div></div></div> |
| <p> |
| The core provides a way to set up centralized exception handling. If |
| an exception takes place during filtering or processing in one of the |
| added sinks, the core will invoke an exception handler if one was installed |
| with the <code class="computeroutput"><span class="identifier">set_exception_handler</span></code> |
| method. An exception handler is a nullary function object that is invoked |
| from within a <code class="computeroutput"><span class="keyword">catch</span></code> clause. |
| The library provides <a class="link" href="detailed/utilities.html#log.detailed.utilities.exception_handlers" title="Exception handlers">tools</a> |
| to simplify exception handlers construction. |
| </p> |
| <div class="tip"><table border="0" summary="Tip"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../../doc/src/images/tip.png"></td> |
| <th align="left">Tip</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| The exception handler in the logging core is global and thus is intended |
| to perform some common actions on errors. Logging sinks and sources |
| also provide exception handling facilities (see <a class="link" href="detailed/sink_frontends.html#log.detailed.sink_frontends.basic_services.exception_handling" title="Exception handling">here</a> |
| and <a class="link" href="detailed/sources.html#log.detailed.sources.exception_handling" title="Loggers with exception handling support">here</a>), |
| which can be used to do a finer grained error processing. |
| </p></td></tr> |
| </table></div> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">my_handler</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="keyword">void</span> <span class="identifier">result_type</span><span class="special">;</span> |
| |
| <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">()</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">runtime_error</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">e</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">cout</span> <span class="special"><<</span> <span class="string">"std::runtime_error: "</span> <span class="special"><<</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</span><span class="special">()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">()</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">logic_error</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">e</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">cout</span> <span class="special"><<</span> <span class="string">"std::logic_error: "</span> <span class="special"><<</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</span><span class="special">()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="keyword">throw</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">};</span> |
| |
| <span class="keyword">void</span> <span class="identifier">init_exception_handler</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="comment">// Setup a global exception handler that will call my_handler::operator()</span> |
| <span class="comment">// for the specified exception types</span> |
| <span class="identifier">logging</span><span class="special">::</span><span class="identifier">core</span><span class="special">::</span><span class="identifier">get</span><span class="special">()-></span><span class="identifier">set_exception_handler</span><span class="special">(</span><span class="identifier">logging</span><span class="special">::</span><span class="identifier">make_exception_handler</span><span class="special"><</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">runtime_error</span><span class="special">,</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">logic_error</span> |
| <span class="special">>(</span><span class="identifier">my_handler</span><span class="special">()));</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="log.detailed.core.core.record_feeding"></a><a class="link" href="detailed.html#log.detailed.core.core.record_feeding" title="Feeding log records">Feeding log |
| records</a> |
| </h5></div></div></div> |
| <p> |
| One of the most important functions of the logging core is providing |
| an entry point for all logging sources to feed log records into. This |
| is done with the <code class="computeroutput"><span class="identifier">open_record</span></code> |
| and <code class="computeroutput"><span class="identifier">push_record</span></code> methods. |
| </p> |
| <p> |
| The first method is used to initiate the record logging process. It accepts |
| the source-specific set of attributes. The method constructs a common |
| set of attribute values of the three sets of attributes (global, thread-specific |
| and source-specific) and applies filtering. If the filtering succeeded, |
| i.e. at least one sink accepts a record with these attribute values, |
| the method returns a non-empty <a class="link" href="detailed.html#log.detailed.core.record" title="Logging records">record |
| object</a>, which can be used to fill in the log record message. If |
| the filtering failed, an empty record object is returned. |
| </p> |
| <p> |
| When the log source is ready to complete the logging procedure, it has |
| to call the <code class="computeroutput"><span class="identifier">push_record</span></code> |
| method with the record returned by the <code class="computeroutput"><span class="identifier">open_record</span></code> |
| method. Note that one should not call <code class="computeroutput"><span class="identifier">push_record</span></code> |
| with an empty record. The record should be passed as rvalue reference. |
| During the call the record view will be constructed from the record. |
| The view will then be passed on to the sinks that accepted it during |
| filtering. This may involve record formatting and further processing, |
| like storing it into a file or sending it over the network. After that |
| the record object can be destroyed. |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">logging_function</span><span class="special">(</span><span class="identifier">logging</span><span class="special">::</span><span class="identifier">attribute_set</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">attrs</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span><span class="special"><</span> <span class="identifier">logging</span><span class="special">::</span><span class="identifier">core</span> <span class="special">></span> <span class="identifier">core</span> <span class="special">=</span> <span class="identifier">logging</span><span class="special">::</span><span class="identifier">core</span><span class="special">::</span><span class="identifier">get</span><span class="special">();</span> |
| |
| <span class="comment">// Attempt to open a log record</span> |
| <span class="identifier">logging</span><span class="special">::</span><span class="identifier">record</span> <span class="identifier">rec</span> <span class="special">=</span> <span class="identifier">core</span><span class="special">-></span><span class="identifier">open_record</span><span class="special">(</span><span class="identifier">attrs</span><span class="special">);</span> |
| <span class="keyword">if</span> <span class="special">(</span><span class="identifier">rec</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="comment">// Ok, the record is accepted. Compose the message now.</span> |
| <span class="identifier">logging</span><span class="special">::</span><span class="identifier">record_ostream</span> <span class="identifier">strm</span><span class="special">(</span><span class="identifier">rec</span><span class="special">);</span> |
| <span class="identifier">strm</span> <span class="special"><<</span> <span class="string">"Hello, World!"</span><span class="special">;</span> |
| <span class="identifier">strm</span><span class="special">.</span><span class="identifier">flush</span><span class="special">();</span> |
| |
| <span class="comment">// Deliver the record to the sinks.</span> |
| <span class="identifier">core</span><span class="special">-></span><span class="identifier">push_record</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">rec</span><span class="special">));</span> |
| <span class="special">}</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| All this logic is usually hidden in the loggers and macros provided by |
| the library. However, this may be useful for those developing new log |
| sources. |
| </p> |
| </div> |
| </div> |
| </div> |
| </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 © 2007-2015 Andrey |
| Semashev<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> |
| </div></td> |
| </tr></table> |
| <hr> |
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