1<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 2<html xmlns="http://www.w3.org/1999/xhtml"> 3<head> 4<meta http-equiv="Content-Type" content="text/xhtml;charset=UTF-8"/> 5<meta http-equiv="X-UA-Compatible" content="IE=9"/> 6<meta name="generator" content="Doxygen 1.8.6"/> 7<title>Boost.Locale: Localized Text Formatting</title> 8<link href="tabs.css" rel="stylesheet" type="text/css"/> 9<script type="text/javascript" src="jquery.js"></script> 10<script type="text/javascript" src="dynsections.js"></script> 11<link href="navtree.css" rel="stylesheet" type="text/css"/> 12<script type="text/javascript" src="resize.js"></script> 13<script type="text/javascript" src="navtree.js"></script> 14<script type="text/javascript"> 15 $(document).ready(initResizable); 16 $(window).load(resizeHeight); 17</script> 18<link href="doxygen.css" rel="stylesheet" type="text/css" /> 19</head> 20<body> 21<div id="top"><!-- do not remove this div, it is closed by doxygen! --> 22<div id="titlearea"> 23<table cellspacing="0" cellpadding="0"> 24 <tbody> 25 <tr style="height: 56px;"> 26 <td id="projectlogo"><img alt="Logo" src="boost-small.png"/></td> 27 <td style="padding-left: 0.5em;"> 28 <div id="projectname">Boost.Locale 29 </div> 30 </td> 31 </tr> 32 </tbody> 33</table> 34</div> 35<!-- end header part --> 36<!-- Generated by Doxygen 1.8.6 --> 37 <div id="navrow1" class="tabs"> 38 <ul class="tablist"> 39 <li><a href="index.html"><span>Main Page</span></a></li> 40 <li class="current"><a href="pages.html"><span>Related Pages</span></a></li> 41 <li><a href="modules.html"><span>Modules</span></a></li> 42 <li><a href="namespaces.html"><span>Namespaces</span></a></li> 43 <li><a href="annotated.html"><span>Classes</span></a></li> 44 <li><a href="files.html"><span>Files</span></a></li> 45 <li><a href="examples.html"><span>Examples</span></a></li> 46 </ul> 47 </div> 48</div><!-- top --> 49<div id="side-nav" class="ui-resizable side-nav-resizable"> 50 <div id="nav-tree"> 51 <div id="nav-tree-contents"> 52 <div id="nav-sync" class="sync"></div> 53 </div> 54 </div> 55 <div id="splitbar" style="-moz-user-select:none;" 56 class="ui-resizable-handle"> 57 </div> 58</div> 59<script type="text/javascript"> 60$(document).ready(function(){initNavTree('localized_text_formatting.html','');}); 61</script> 62<div id="doc-content"> 63<div class="header"> 64 <div class="headertitle"> 65<div class="title">Localized Text Formatting </div> </div> 66</div><!--header--> 67<div class="contents"> 68<div class="textblock"><p>The <code>iostream</code> manipulators are very useful, but when we create a messages for the user, sometimes we need something like good old <code>printf</code> or <code>boost::format</code>.</p> 69<p>Unfortunately <code>boost::format</code> has several limitations in context of localization:</p> 70<ol type="1"> 71<li>It renders all parameters using global locale rather than target <code>ostream</code> locale. For example: <br/> 72<div class="fragment"><div class="line">std::locale::global(std::locale(<span class="stringliteral">"en_US.UTF-8"</span>));</div> 73<div class="line">output.imbue(std::locale(<span class="stringliteral">"de_DE.UTF-8"</span>))</div> 74<div class="line">output << <a class="code" href="group__format.html#gad7914df7b54382c1ad7f5360676fe2e8">boost::format</a>(<span class="stringliteral">"%1%"</span>) % 1234.345;</div> 75</div><!-- fragment --> <br/> 76 This would write "1,234.235" to output, instead of the "1.234,234" that is expected for "de_DE" locale</li> 77<li>It knows nothing about the new Boost.Locale manipulators.</li> 78<li>The <code>printf-like</code> syntax is very limited for formatting complex localized data, not allowing the formatting of dates, times, or currencies</li> 79</ol> 80<p>Thus a new class, <a class="el" href="group__format.html#gad7914df7b54382c1ad7f5360676fe2e8">boost::locale::format</a>, was introduced. For example:</p> 81<div class="fragment"><div class="line">wcout << <a class="code" href="group__format.html#ga610f3ae827801febc962019cf82a2227">wformat</a>(L<span class="stringliteral">"Today {1,date} I would meet {2} at home"</span>) % <a class="code" href="group__manipulators.html#gae669b101cbeaed6f6d246ebdcaa8f39c">time</a>(0) % name <<endl;</div> 82</div><!-- fragment --><p>Each format specifier is enclosed within <code>{}</code> brackets, is separated with a comma "," and may have an additional option after an equals symbol '='. This option may be simple ASCII text or single-quoted localized text. If a single-quote should be inserted within the text, it may be represented with a pair of single-quote characters.</p> 83<p>Here is an example of a format string:</p> 84<pre class="fragment"> "Ms. {1} had arrived at {2,ftime='%I o''clock'} at home. The exact time is {2,time=full}" 85</pre><p>The syntax is described by following grammar:</p> 86<pre class="fragment"> format : '{' parameters '}' 87 parameters: parameter | parameter ',' parameters; 88 parameter : key ["=" value] ; 89 key : [0-9a-zA-Z<>]+ ; 90 value : ascii-string-excluding-"}"-and="," | local-string ; 91 local-string : quoted-text | quoted-text local-string; 92 quoted-text : '[^']*' ; 93</pre><p>You can include literal '{' and '}' by inserting double "{{" or "}}" to the text.</p> 94<div class="fragment"><div class="line">cout << <a class="code" href="group__format.html#gad7914df7b54382c1ad7f5360676fe2e8">format</a>(<a class="code" href="group__message.html#ga58e9599005608845d2b022d499dc97f6">translate</a>(<span class="stringliteral">"Unexpected `{{' in line {1} in file {2}"</span>)) % pos % file;</div> 95</div><!-- fragment --><p>Would display something like</p> 96<pre class="fragment">Unexpected `{' in line 5 in file source.cpp 97</pre><p>The following format key-value pairs are supported:</p> 98<ul> 99<li><code>[0-9]+</code> – digits, the index of the formatted parameter – required.</li> 100<li><code>num</code> or <code>number</code> – format a number. Options are: <br/> 101<ul> 102<li><code>hex</code> – display in hexadecimal format</li> 103<li><code>oct</code> – display in octal format</li> 104<li><code>sci</code> or <code>scientific</code> – display in scientific format</li> 105<li><code>fix</code> or <code>fixed</code> – display in fixed format <br/> 106 For example, <code>number=sci</code> </li> 107</ul> 108</li> 109<li><code>cur</code> or <code>currency</code> – format currency. Options are: <br/> 110<ul> 111<li><code>iso</code> – display using ISO currency symbol.</li> 112<li><code>nat</code> or <code>national</code> – display using national currency symbol. <br/> 113</li> 114</ul> 115</li> 116<li><code>per</code> or <code>percent</code> – format a percentage value.</li> 117<li><code>date</code>, <code>time</code>, <code>datetime</code> or <code>dt</code> – format a date, a time, or a date and time. Options are: <br/> 118<ul> 119<li><code>s</code> or <code>short</code> – display in short format.</li> 120<li><code>m</code> or <code>medium</code> – display in medium format.</li> 121<li><code>l</code> or <code>long</code> – display in long format.</li> 122<li><code>f</code> or <code>full</code> – display in full format.</li> 123</ul> 124</li> 125<li><code>ftime</code> with string (quoted) parameter – display as with <code>strftime</code>. See <code>as::ftime</code> manipulator.</li> 126<li><code>spell</code> or <code>spellout</code> – spell the number.</li> 127<li><code>ord</code> or <code>ordinal</code> – format an ordinal number (1st, 2nd... etc)</li> 128<li><code>left</code> or <code><</code> – align-left.</li> 129<li><code>right</code> or <code>></code> – align-right.</li> 130<li><code>width</code> or <code>w</code> – set field width (requires parameter).</li> 131<li><code>precision</code> or <code>p</code> – set precision (requires parameter).</li> 132<li><code>locale</code> – with parameter – switch locales for the current operation. This command generates a locale with formatting facets, giving more fine grained control of formatting. For example: <br/> 133<div class="fragment"><div class="line">cout << <a class="code" href="group__format.html#gad7914df7b54382c1ad7f5360676fe2e8">format</a>(<span class="stringliteral">"This article was published at {1,date=l} (Gregorian) {1,locale=he_IL@calendar=hebrew,date=l} (Hebrew)"</span>) % <a class="code" href="group__manipulators.html#gae05b82e6658dc573521518fed5f5c77f">date</a>;</div> 134</div><!-- fragment --></li> 135<li><code>timezone</code> or <code>tz</code> – the name of the timezone to display the time in. For example:<br/> 136<div class="fragment"><div class="line">cout << <a class="code" href="group__format.html#gad7914df7b54382c1ad7f5360676fe2e8">format</a>(<span class="stringliteral">"Time is: Local {1,time}, ({1,time,tz=EET} Eastern European Time)"</span>) % <a class="code" href="group__manipulators.html#gae05b82e6658dc573521518fed5f5c77f">date</a>;</div> 137</div><!-- fragment --></li> 138<li><code>local</code> - display the time in local time</li> 139<li><code>gmt</code> - display the time in UTC time scale <div class="fragment"><div class="line">cout << <a class="code" href="group__format.html#gad7914df7b54382c1ad7f5360676fe2e8">format</a>(<span class="stringliteral">"Local time is: {1,time,local}, universal time is {1,time,gmt}"</span>) % <a class="code" href="group__manipulators.html#gae669b101cbeaed6f6d246ebdcaa8f39c">time</a>;</div> 140</div><!-- fragment --></li> 141</ul> 142<p>The constructor for the <a class="el" href="group__format.html#gad7914df7b54382c1ad7f5360676fe2e8">format</a> class can take an object of type <a class="el" href="group__message.html#ga556e3e7696302902b2242a7a94516dee">message</a>, simplifying integration with message translation code.</p> 143<p>For example:</p> 144<div class="fragment"><div class="line">cout<< <a class="code" href="group__format.html#gad7914df7b54382c1ad7f5360676fe2e8">format</a>(<a class="code" href="group__message.html#ga58e9599005608845d2b022d499dc97f6">translate</a>(<span class="stringliteral">"Adding {1} to {2}, we get {3}"</span>)) % a % b % (a+b) << endl;</div> 145</div><!-- fragment --><p>A formatted string can be fetched directly by using the <a class="el" href="classboost_1_1locale_1_1basic__format.html#a6bc65d7993e3ab6ad51809ef8fb65400">str(std::locale const &loc=std::locale())</a> member function. For example:</p> 146<div class="fragment"><div class="line">std::wstring de = (<a class="code" href="group__format.html#ga610f3ae827801febc962019cf82a2227">wformat</a>(<a class="code" href="group__message.html#ga58e9599005608845d2b022d499dc97f6">translate</a>(<span class="stringliteral">"Adding {1} to {2}, we get {3}"</span>)) % a % b % (a+b)).str(de_locale);</div> 147<div class="line">std::wstring fr = (<a class="code" href="group__format.html#ga610f3ae827801febc962019cf82a2227">wformat</a>(<a class="code" href="group__message.html#ga58e9599005608845d2b022d499dc97f6">translate</a>(<span class="stringliteral">"Adding {1} to {2}, we get {3}"</span>)) % a % b % (a+b)).str(fr_locale);</div> 148</div><!-- fragment --><dl class="section note"><dt>Note</dt><dd>There is one significant difference between <code>boost::format</code> and <code><a class="el" href="group__format.html#gad7914df7b54382c1ad7f5360676fe2e8">boost::locale::format</a></code>: Boost.Locale's format converts its parameters only when written to an <code>ostream</code> or when the <code>str()</code> member function is called. It only saves references to the objects that can be written to a stream.</dd></dl> 149<p>This is generally not a problem when all operations are done in one statement, such as:</p> 150<div class="fragment"><div class="line">cout << <a class="code" href="group__format.html#gad7914df7b54382c1ad7f5360676fe2e8">format</a>(<span class="stringliteral">"Adding {1} to {2}, we get {3}"</span>) % a % b % (a+b);</div> 151</div><!-- fragment --><p>Because the temporary value of <code></code>(a+b) exists until the formatted data is actually written to the stream. But following code is wrong:</p> 152<div class="fragment"><div class="line"><a class="code" href="group__format.html#gad7914df7b54382c1ad7f5360676fe2e8">format</a> fmt(<span class="stringliteral">"Adding {1} to {2}, we get {3}"</span>);</div> 153<div class="line">fmt % a;</div> 154<div class="line">fmt % b;</div> 155<div class="line">fmt % (a+b);</div> 156<div class="line">cout << fmt;</div> 157</div><!-- fragment --><p>Because the temporary value of <code></code>(a+b) no longer exists when <code>fmt</code> is written to the stream. A correct solution would be:</p> 158<div class="fragment"><div class="line"><a class="code" href="group__format.html#gad7914df7b54382c1ad7f5360676fe2e8">format</a> fmt(<span class="stringliteral">"Adding {1} to {2}, we get {3}"</span>);</div> 159<div class="line">fmt % a;</div> 160<div class="line">fmt % b;</div> 161<div class="line"><span class="keywordtype">int</span> a_plus_b = a+b;</div> 162<div class="line">fmt % a_plus_b;</div> 163<div class="line">cout << fmt;</div> 164</div><!-- fragment --> </div></div><!-- contents --> 165</div><!-- doc-content --> 166 167 <li class="footer"> 168© Copyright 2009-2012 Artyom Beilis, Distributed under the <a href="http://www.boost.org/LICENSE_1_0.txt">Boost Software License</a>, Version 1.0. 169 </li> 170 </ul> 171 </div> 172</body> 173</html> 174
