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<refentry xml:id="function.strspn" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>strspn</refname>
  <refpurpose>
   Finds the length of the initial segment of a string consisting
   entirely of characters contained within a given mask
  </refpurpose>
 </refnamediv>
 
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>int</type><methodname>strspn</methodname>
   <methodparam><type>string</type><parameter>string</parameter></methodparam>
   <methodparam><type>string</type><parameter>characters</parameter></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>offset</parameter><initializer>0</initializer></methodparam>
   <methodparam choice="opt"><type class="union"><type>int</type><type>null</type></type><parameter>length</parameter><initializer>&null;</initializer></methodparam>
  </methodsynopsis>
  <para>
   Finds the length of the initial segment of <parameter>string</parameter>
   that contains <emphasis>only</emphasis> characters from <parameter>characters</parameter>.
  </para>
  <para>
   If <parameter>offset</parameter> and <parameter>length</parameter>
   are omitted, then all of <parameter>string</parameter> will be
   examined. If they are included, then the effect will be the same as
   calling <literal>strspn(substr($string, $offset, $length),
   $characters)</literal> (see <xref linkend="function.substr"/>
   for more information).
  </para>
  <para>
   The line of code:
   <informalexample>
    <programlisting role="php">
<![CDATA[
<?php
$var = strspn("42 is the answer to the 128th question.", "1234567890");
?>
]]>
    </programlisting>
   </informalexample>
   will assign <literal>2</literal> to <varname>$var</varname>,
   because the string "42" is the initial segment
   of <parameter>string</parameter> that consists only of characters
   contained within "1234567890".
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>string</parameter></term>
     <listitem>
      <para>
       The string to examine.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>characters</parameter></term>
     <listitem>
      <para>
       The list of allowable characters.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>offset</parameter></term>
     <listitem>
      <para>
       The position in <parameter>string</parameter> to
       start searching.
      </para>
      <para>
       If <parameter>offset</parameter> is given and is non-negative,
       then <function>strspn</function> will begin
       examining <parameter>string</parameter> at
       the <parameter>offset</parameter>'th position. For instance, in
       the string '<literal>abcdef</literal>', the character at
       position <literal>0</literal> is '<literal>a</literal>', the
       character at position <literal>2</literal> is
       '<literal>c</literal>', and so forth.
      </para>
      <para>
       If <parameter>offset</parameter> is given and is negative,
       then <function>strspn</function> will begin
       examining <parameter>string</parameter> at
       the <parameter>offset</parameter>'th position from the end
       of <parameter>string</parameter>.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>length</parameter></term>
     <listitem>
      <para>
       The length of the segment from <parameter>string</parameter>
       to examine. 
      </para>
      <para>
       If <parameter>length</parameter> is given and is non-negative,
       then <parameter>string</parameter> will be examined
       for <parameter>length</parameter> characters after the starting
       position.
      </para>
      <para>
        If <parameter>length</parameter> is given and is negative,
        then <parameter>string</parameter> will be examined from the
        starting position up to <parameter>length</parameter>
        characters from the end of <parameter>string</parameter>.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns the length of the initial segment of <parameter>string</parameter>
   which consists entirely of characters in <parameter>characters</parameter>.
  </para>
  <note>
   <para>
    When a <parameter>offset</parameter> parameter is set, the returned length
    is counted starting from this position, not from the beginning of
    <parameter>string</parameter>.
   </para>
  </note>
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <informaltable>
   <tgroup cols="2">
    <thead>
     <row>
      <entry>&Version;</entry>
      <entry>&Description;</entry>
     </row>
    </thead>
    <tbody>
     <row>
      <entry>8.0.0</entry>
      <entry>
       <parameter>length</parameter> is nullable now.
      </entry>
     </row>
    </tbody>
   </tgroup>
  </informaltable>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>strspn</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
// subject does not start with any characters from mask
var_dump(strspn("foo", "o"));

// examine two characters from subject starting at offset 1
var_dump(strspn("foo", "o", 1, 2));

// examine one character from subject starting at offset 1
var_dump(strspn("foo", "o", 1, 1));
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
int(0)
int(2)
int(1)
]]>
    </screen>
   </example>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  &note.bin-safe;
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>strcspn</function></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>
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