1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Definitions</title> 5<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="Chapter 1. Boost.Log v2"> 8<link rel="up" href="../index.html" title="Chapter 1. Boost.Log v2"> 9<link rel="prev" href="installation/config.html" title="Configuring and building the library"> 10<link rel="next" href="design.html" title="Design overview"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr><td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td></tr></table> 14<hr> 15<div class="spirit-nav"> 16<a accesskey="p" href="installation/config.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="design.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 17</div> 18<div class="section"> 19<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 20<a name="log.defs"></a><a class="link" href="defs.html" title="Definitions">Definitions</a> 21</h2></div></div></div> 22<p> 23 Here are definitions of some terms that will be used widely throughout the 24 documentation: 25 </p> 26<div class="variablelist"> 27<p class="title"><b></b></p> 28<dl class="variablelist"> 29<dt><span class="term">Log record</span></dt> 30<dd><p> 31 A single bundle of information, collected from the user's application, 32 that is a candidate to be put into the log. In a simple case the log 33 record will be represented as a line of text in the log file after being 34 processed by the logging library. 35 </p></dd> 36<dt><span class="term">Attribute</span></dt> 37<dd><p> 38 An "attribute" is a piece of meta-information that can be used 39 to specialize a log record. In Boost.Log attributes are represented by 40 function objects with a specific interface, which return the actual attribute 41 value when invoked. 42 </p></dd> 43<dt><span class="term">Attribute value</span></dt> 44<dd><p> 45 Attribute values are the actual data acquired from attributes. This data 46 is attached to the specific log record and processed by the library. 47 Values can have different types (integers, strings and more complex, 48 including user defined types). Some examples of attribute values: current 49 time stamp value, file name, line number, current scope name, etc.. Attribute 50 values are enveloped in a type erasing wrapper, so the actual type of 51 the attribute is not visible in the interface. The actual (erased) type 52 of the value is sometimes called the stored type. 53 </p></dd> 54<dt><span class="term">(Attribute) value visitation</span></dt> 55<dd><p> 56 A way of processing the attribute value. This approach involves a function 57 object (a visitor) which is applied to the attribute value. The visitor 58 should know the stored type of the attribute value in order to process 59 it. 60 </p></dd> 61<dt><span class="term">(Attribute) value extraction</span></dt> 62<dd><p> 63 A way of processing the attribute value when the caller attempts to obtain 64 a reference to the stored value. The caller should know the stored type 65 of the attribute value in order to be able to extract it. 66 </p></dd> 67<dt><span class="term">Log sink</span></dt> 68<dd><p> 69 A target, to which all log records are fed after being collected from 70 the user's application. The sink defines where and how the log records 71 are going to be stored or processed. 72 </p></dd> 73<dt><span class="term">Log source</span></dt> 74<dd><p> 75 An entry point for the user's application to put log records to. In a 76 simple case it is an object (logger) which maintains a set of attributes 77 that will be used to form a log record upon the user's request. However, 78 one can surely create a source that would emit log records on some side 79 events (for example, by intercepting and parsing console output of another 80 application). 81 </p></dd> 82<dt><span class="term">Log filter</span></dt> 83<dd><p> 84 A predicate that takes a log record and tells whether this record should 85 be passed through or discarded. The predicate typically forms its decision 86 based on the attribute values attached to the record. 87 </p></dd> 88<dt><span class="term">Log formatter</span></dt> 89<dd><p> 90 A function object that generates the final textual output from a log 91 record. Some sinks, e.g. a binary logging sink, may not need it, although 92 almost any text-based sink would use a formatter to compose its output. 93 </p></dd> 94<dt><span class="term">Logging core</span></dt> 95<dd><p> 96 The global entity that maintains connections between sources and sinks 97 and applies filters to records. It is mainly used when the logging library 98 is initialized. 99 </p></dd> 100<dt><span class="term">i18n</span></dt> 101<dd><p> 102 Internationalization. The ability to manipulate wide characters. 103 </p></dd> 104<dt><span class="term">TLS</span></dt> 105<dd><p> 106 Thread-local storage. The concept of having a variable that has independent 107 values for each thread that attempts to access it. 108 </p></dd> 109<dt><span class="term">RTTI</span></dt> 110<dd><p> 111 Run-time type information. This is the C++ language support data structures 112 required for <code class="computeroutput"><span class="keyword">dynamic_cast</span></code> 113 and <code class="computeroutput"><span class="keyword">typeid</span></code> operators to 114 function properly. 115 </p></dd> 116</dl> 117</div> 118</div> 119<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 120<td align="left"></td> 121<td align="right"><div class="copyright-footer">Copyright © 2007-2019 Andrey Semashev<p> 122 Distributed under the Boost Software License, Version 1.0. (See accompanying 123 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>). 124 </p> 125</div></td> 126</tr></table> 127<hr> 128<div class="spirit-nav"> 129<a accesskey="p" href="installation/config.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="design.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 130</div> 131</body> 132</html> 133
