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<h1 class="title">Introduction</h1>
<p class="para">
The functions provided by this extension check whether a character
or string falls into a certain character class according to the
current locale (see also <span class="function"><a href="function.setlocale.html" class="function">setlocale()</a></span>).
</p>
<p class="para">
When called with an integer argument these functions
behave exactly like their C counterparts from
<var class="filename">ctype.h</var>.
It means that if you pass an integer smaller than 256 it will use the
ASCII value of it to see if it fits in the specified range (digits are in
0x30-0x39). If the number is between -128 and -1 inclusive then 256 will
be added and the check will be done on that.
</p>
<p class="para">
When called with a string argument they will check
every character in the string and will only return
<strong><code>TRUE</code></strong> if every character in the string matches the
requested criteria. When called with an empty string
the result will always be <strong><code>TRUE</code></strong> in PHP < 5.1 and <strong><code>FALSE</code></strong> since 5.1.
</p>
<p class="para">
Passing anything else but a string or integer will
return <strong><code>FALSE</code></strong> immediately.
</p>
<p class="para">
It should be noted that ctype functions are always preferred over
regular expressions, and even to some equivalent <em>"str_*"</em> and <em>"is_*"</em> functions.
This is because of the fact that ctype uses a native C library and thus
processes significantly faster.
</p>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
These functions are not related to the Python "ctypes" library at all.
The extension name stems from the <var class="filename">ctype.h</var> C header
file that their C equivalents are defined in.
</p>
<p class="para">
This extension also predates Python "ctypes" so any confusion
caused by this naming is hardly our fault ...
</p>
</p></blockquote>
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