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libstdc++: Add lambda example to case transformation docs

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libstdc++-v3/ChangeLog:

	* doc/xml/manual/strings.xml: Tweak formatting. Add example
	using lambda.
	* doc/html/manual/strings.html: Regenerate.
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Jonathan Wakely 2025-03-12 11:30:04 +00:00 • committed by Jonathan Wakely
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19
libstdc++-v3/doc/html/manual/strings.html
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@ -50,10 +50,12 @@
</pre><p>
<span class="emphasis"><em>Note</em></span> that these calls all
involve the global C locale through the use of the C functions
<code class="code">toupper/tolower</code>. This is absolutely guaranteed to work --
but <span class="emphasis"><em>only</em></span> if the string contains <span class="emphasis"><em>only</em></span> characters
from the basic source character set, and there are <span class="emphasis"><em>only</em></span>
96 of those. Which means that not even all English text can be
<code class="code">toupper</code>/<code class="code">tolower</code>.
This is absolutely guaranteed to work
-- but <span class="emphasis"><em>only</em></span> if the string contains
<span class="emphasis"><em>only</em></span> characters from the basic source character set,
and there are <span class="emphasis"><em>only</em></span> 96 of those.
Which means that not even all English text can be
represented (certain British spellings, proper names, and so forth).
So, if all your input forevermore consists of only those 96
characters (hahahahahaha), then you're done.
@ -73,7 +75,14 @@
// std::tolower(c) is undefined if c &lt; 0 so cast to unsigned char.
return std::tolower((unsigned char)c);
} </pre><p>(Thanks to James Kanze for assistance and suggestions on all of this.)
</p><p>Another common operation is trimming off excess whitespace. Much
</p><p>
Since C++11 the wrapper can be replaced with a lambda expression,
which can perform the conversion to <code class="code">unsigned char</code> and
also ensure the single-argument form of <code class="code">std::lower</code> is used:
</p><pre class="programlisting">
std::transform (s.begin(), s.end(), capital_s.begin(),
[](unsigned char c) { return std::tolower(c); });
</pre><p>Another common operation is trimming off excess whitespace. Much
like transformations, this task is trivial with the use of string's
<code class="code">find</code> family. These examples are broken into multiple
statements for readability:

19
libstdc++-v3/doc/xml/manual/strings.xml
View file

@ -66,10 +66,12 @@
<para>
<emphasis>Note</emphasis> that these calls all
involve the global C locale through the use of the C functions
<code>toupper/tolower</code>. This is absolutely guaranteed to work --
but <emphasis>only</emphasis> if the string contains <emphasis>only</emphasis> characters
from the basic source character set, and there are <emphasis>only</emphasis>
96 of those. Which means that not even all English text can be
<code>toupper</code>/<code>tolower</code>.
This is absolutely guaranteed to work
-- but <emphasis>only</emphasis> if the string contains
<emphasis>only</emphasis> characters from the basic source character set,
and there are <emphasis>only</emphasis> 96 of those.
Which means that not even all English text can be
represented (certain British spellings, proper names, and so forth).
So, if all your input forevermore consists of only those 96
characters (hahahahahaha), then you're done.
@ -93,6 +95,15 @@
} </programlisting>
<para>(Thanks to James Kanze for assistance and suggestions on all of this.)
</para>
<para>
Since C++11 the wrapper can be replaced with a lambda expression,
which can perform the conversion to <code>unsigned char</code> and
also ensure the single-argument form of <code>std::lower</code> is used:
</para>
<programlisting>
std::transform (s.begin(), s.end(), capital_s.begin(),
[](unsigned char c) { return std::tolower(c); });
</programlisting>
<para>Another common operation is trimming off excess whitespace. Much
like transformations, this task is trivial with the use of string's
<code>find</code> family. These examples are broken into multiple