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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<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.
<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>
</para>
</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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