archived-doc-en/language/types/numeric-strings.xml

<?xml version="1.0" encoding="utf-8"?>
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<sect1 xml:id="language.types.numeric-strings" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <title>Numeric strings</title>
 <para>
  A PHP <type>string</type> is considered numeric if it can be interpreted as
  an <type>int</type> or a <type>float</type>.
 </para>

 <para>
  Formally as of PHP 8.0.0:
 </para>

 <informalexample>
  <programlisting>
   <![CDATA[
WHITESPACES      \s*
LNUM             [0-9]+
DNUM             ([0-9]*[\.]{LNUM}) | ({LNUM}[\.][0-9]*)
EXPONENT_DNUM    (({LNUM} | {DNUM}) [eE][+-]? {LNUM})
INT_NUM_STRING   {WHITESPACES} [+-]? {LNUM} {WHITESPACES}
FLOAT_NUM_STRING {WHITESPACES} [+-]? ({DNUM} | {EXPONENT_DNUM}) {WHITESPACES}
NUM_STRING       ({INT_NUM_STRING} | {FLOAT_NUM_STRING})
]]>
  </programlisting>
 </informalexample>

 <para>
  PHP also has a concept of <emphasis>leading</emphasis> numeric strings.
  This is simply a string which starts like a numeric string followed by
  any characters.
 </para>

 <note>
  <para>
   Any string that contains the letter <literal>E</literal> (case insensitive)
   bounded by numbers will be seen as a number expressed in scientific notation.
   This can produce unexpected results.
  </para>
  <example>
   <title>Scientific Notation Comparisons</title>
   <programlisting role="php">
<![CDATA[
<?php
var_dump("0D1" == "000"); // false, "0D1" is not scientific notation
var_dump("0E1" == "000"); // true, "0E1" is 0 * (10 ^ 1), or 0
var_dump("2E1" == "020"); // true, "2E1" is 2 * (10 ^ 1), or 20
?>
]]>
   </programlisting>
  </example>
 </note>

 <sect2 xml:id="language.types.numeric-string.conversion">
  <title>Strings used in numeric contexts</title>
  <para>
   When a <type>string</type> needs to be evaluated as number (e.g. arithmetic
   operations, <type>int</type> type declaration, etc.) the following
   steps are taken to determine the outcome:

   <orderedlist>
    <listitem>
     <simpara>
      If the <type>string</type> is numeric, resolve to an <type>int</type> if
      the <type>string</type> is an integer numeric string and fits into the
      limits of the <type>int</type> type limits (as defined by
      <constant>PHP_INT_MAX</constant>), otherwise resolve to a
      <type>float</type>.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      If the context allows leading numeric strings and the <type>string</type>
      is one, resolve to an <type>int</type> if the leading part of the
      <type>string</type> is an integer numeric string and fits into the
      limits of the <type>int</type> type limits (as defined by
      <constant>PHP_INT_MAX</constant>), otherwise resolve to a
      <type>float</type>.
      Additionally an error of level <constant>E_WARNING</constant> is raised.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      The <type>string</type> is not numeric, throw a
      <classname>TypeError</classname>.
     </simpara>
    </listitem>
   </orderedlist>
  </para>
 </sect2>

 <sect2 xml:id="language.types.numeric-string.prior">
  <title>Behavior prior to PHP 8.0.0</title>
  <para>
   Prior to PHP 8.0.0, a <type>string</type> was considered numeric only if it
   had <emphasis>leading</emphasis> whitespaces, if it had
   <emphasis>trailing</emphasis> whitespaces then the string was considered to
   be leading numeric.
  </para>

  <para>
   Prior to PHP 8.0.0, when a string was used in a numeric context it would
   perform the same steps as above with the following differences:
   <itemizedlist>
    <listitem>
     <simpara>
      The usage of a leading numeric string would raise an
      <constant>E_NOTICE</constant> instead of an <constant>E_WARNING</constant>.
     </simpara>
     </listitem>
    <listitem>
     <simpara>
      If the string is not numeric, an <constant>E_WARNING</constant> was
      raised and the value <literal>0</literal> would be returned.
     </simpara>
    </listitem>
   </itemizedlist>
   Prior to PHP 7.1.0, neither <constant>E_NOTICE</constant>
   nor <constant>E_WARNING</constant> was raised.
  </para>

  <informalexample>
   <programlisting role="php">
<![CDATA[
<?php
$foo = 1 + "10.5";                // $foo is float (11.5)
$foo = 1 + "-1.3e3";              // $foo is float (-1299)
$foo = 1 + "bob-1.3e3";           // TypeError as of PHP 8.0.0, $foo is integer (1) previously
$foo = 1 + "bob3";                // TypeError as of PHP 8.0.0, $foo is integer (1) previously
$foo = 1 + "10 Small Pigs";       // $foo is integer (11) and an E_WARNING is raised in PHP 8.0.0, E_NOTICE previously
$foo = 4 + "10.2 Little Piggies"; // $foo is float (14.2) and an E_WARNING is raised in PHP 8.0.0, E_NOTICE previously
$foo = "10.0 pigs " + 1;          // $foo is float (11) and an E_WARNING is raised in PHP 8.0.0, E_NOTICE previously
$foo = "10.0 pigs " + 1.0;        // $foo is float (11) and an E_WARNING is raised in PHP 8.0.0, E_NOTICE previously
?>
]]>
   </programlisting>
  </informalexample>
 </sect2>
</sect1>
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