language/types/integer.xml
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<title>Integers</title>
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<simpara>
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An <type>integer</type> is a number of the set
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An <type>int</type> is a number of the set
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&#8484; = {..., -2, -1, 0, 1, 2, ...}.
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</simpara>
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<para>
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See also:
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</para>
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<itemizedlist>
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<listitem>
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<simpara>
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<link linkend="ref.gmp">Arbitrary length integer / GMP</link>
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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<link linkend="language.types.float">Floating point numbers</link>
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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<link linkend="ref.bc">Arbitrary precision / BCMath</link>
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</simpara>
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</listitem>
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</itemizedlist>
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<sect2 role="seealso">
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&reftitle.seealso;
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<para>
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<simplelist>
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<member><link linkend="language.types.float">Floating point numbers</link></member>
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<member><link linkend="book.bc">Arbitrary precision / BCMath</link></member>
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<member><link linkend="book.gmp">Arbitrary length integer / GMP</link></member>
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</simplelist>
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</para>
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</sect2>
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<sect2 xml:id="language.types.integer.syntax">
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<title>Syntax</title>
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<simpara>
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<type>Integer</type>s can be specified in decimal (base 10), hexadecimal
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(base 16), octal (base 8) or binary (base 2) notation, optionally preceded by a sign
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(- or +).
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<type>Int</type>s can be specified in decimal (base 10), hexadecimal
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(base 16), octal (base 8) or binary (base 2) notation.
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The <link linkend="language.operators.arithmetic">negation operator</link>
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can be used to denote a negative <type>int</type>.
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</simpara>
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<para>
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Binary <type>integer</type> literals are available since PHP 5.4.0.
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</para>
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<para>
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To use octal notation, precede the number with a <literal>0</literal> (zero).
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As of PHP 8.1.0, octal notation can also be preceded with <literal>0o</literal> or <literal>0O</literal>.
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To use hexadecimal notation precede the number with <literal>0x</literal>.
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To use binary notation precede the number with <literal>0b</literal>.
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</para>
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<para>
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As of PHP 7.4.0, integer literals may contain underscores (<literal>_</literal>) between digits,
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for better readability of literals. These underscores are removed by PHP's scanner.
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</para>
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<example>
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<title>Integer literals</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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$a = 1234; // decimal number
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$a = -123; // a negative number
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$a = 0123; // octal number (equivalent to 83 decimal)
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$a = 0o123; // octal number (as of PHP 8.1.0)
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$a = 0x1A; // hexadecimal number (equivalent to 26 decimal)
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$a = 0b11111111; // binary number (equivalent to 255 decimal)
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$a = 1_234_567; // decimal number (as of PHP 7.4.0)
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?>
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]]>
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</programlisting>
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</example>
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<para>
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Formally, the structure for <type>integer</type> literals is:
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Formally, the structure for <type>int</type> literals is as of PHP 8.1.0
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(previously, the <literal>0o</literal> or <literal>0O</literal> octal
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prefixes were not allowed, and prior to PHP 7.4.0 the underscores were
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not allowed):
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</para>
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<informalexample>
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<programlisting>
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<![CDATA[
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decimal : [1-9][0-9]*
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decimal : [1-9][0-9]*(_[0-9]+)*
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| 0
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hexadecimal : 0[xX][0-9a-fA-F]+
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hexadecimal : 0[xX][0-9a-fA-F]+(_[0-9a-fA-F]+)*
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octal : 0[0-7]+
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octal : 0[oO]?[0-7]+(_[0-7]+)*
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binary : 0b[01]+
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binary : 0[bB][01]+(_[01]+)*
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integer : [+-]?decimal
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| [+-]?hexadecimal
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| [+-]?octal
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| [+-]?binary
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integer : decimal
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| hexadecimal
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| octal
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| binary
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]]>
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</programlisting>
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</informalexample>
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<para>
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The size of an <type>integer</type> is platform-dependent, although a maximum
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The size of an <type>int</type> is platform-dependent, although a maximum
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value of about two billion is the usual value (that's 32 bits signed).
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64-bit platforms usually have a maximum value of about 9E18, except for
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Windows, which is always 32 bit. PHP does not support unsigned
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<type>integer</type>s. <type>Integer</type> size can be determined using
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the constant <constant>PHP_INT_SIZE</constant>, and maximum value using the
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constant <constant>PHP_INT_MAX</constant> since PHP 4.4.0 and PHP 5.0.5.
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64-bit platforms usually have a maximum value of about 9E18.
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PHP does not support unsigned <type>int</type>s.
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<type>int</type> size can be determined
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using the constant <constant>PHP_INT_SIZE</constant>, maximum value using
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the constant <constant>PHP_INT_MAX</constant>,
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and minimum value using the constant <constant>PHP_INT_MIN</constant>.
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</para>
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<warning>
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<para>
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If an invalid digit is given in an octal <type>integer</type> (i.e. 8 or 9),
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the rest of the number is ignored.
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</para>
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<example>
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<title>Octal weirdness</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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var_dump(01090); // 010 octal = 8 decimal
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?>
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]]>
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</programlisting>
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</example>
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</warning>
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</sect2>
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<sect2 xml:id="language.types.integer.overflow">
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<title>Integer overflow</title>
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<para>
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If PHP encounters a number beyond the bounds of the <type>integer</type>
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If PHP encounters a number beyond the bounds of the <type>int</type>
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type, it will be interpreted as a <type>float</type> instead. Also, an
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operation which results in a number beyond the bounds of the
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<type>integer</type> type will return a <type>float</type> instead.
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<type>int</type> type will return a <type>float</type> instead.
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</para>
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<example>
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</example>
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<para>
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There is no <type>integer</type> division operator in PHP.
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There is no <type>int</type> division operator in PHP, to achieve this
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use the <function>intdiv</function> function.
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<literal>1/2</literal> yields the <type>float</type> <literal>0.5</literal>.
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The value can be casted to an <type>integer</type> to round it downwards, or
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The value can be cast to an <type>int</type> to round it towards zero, or
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the <function>round</function> function provides finer control over rounding.
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</para>
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<title>Converting to integer</title>
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<simpara>
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To explicitly convert a value to <type>integer</type>, use either the
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To explicitly convert a value to <type>int</type>, use either the
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<literal>(int)</literal> or <literal>(integer)</literal> casts. However, in
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most cases the cast is not needed, since a value will be automatically
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converted if an operator, function or control structure requires an
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<type>integer</type> argument. A value can also be converted to
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<type>integer</type> with the <function>intval</function> function.
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<type>int</type> argument. A value can also be converted to
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<type>int</type> with the <function>intval</function> function.
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</simpara>
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<simpara>
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If a <type>resource</type> is converted to an <type>integer</type>, then
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If a <type>resource</type> is converted to an <type>int</type>, then
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the result will be the unique resource number assigned to the
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<type>resource</type> by PHP at runtime.
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</simpara>
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</title>
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<simpara>
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When converting from <type>float</type> to <type>integer</type>, the number
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When converting from <type>float</type> to <type>int</type>, the number
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will be rounded <emphasis>towards zero</emphasis>.
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As of PHP 8.1.0, a deprecation notice is emitted when implicitly converting a non-integral &float; to &integer; which loses precision.
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</simpara>
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<programlisting role="php">
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<![CDATA[
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<?php
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function foo($value): int {
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return $value;
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}
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var_dump(foo(8.1)); // "Deprecated: Implicit conversion from float 8.1 to int loses precision" as of PHP 8.1.0
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var_dump(foo(8.1)); // 8 prior to PHP 8.1.0
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var_dump(foo(8.0)); // 8 in both cases
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var_dump((int)8.1); // 8 in both cases
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var_dump(intval(8.1)); // 8 in both cases
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?>
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]]>
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</programlisting>
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<para>
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If the float is beyond the boundaries of <type>integer</type> (usually
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If the float is beyond the boundaries of <type>int</type> (usually
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<literal>+/- 2.15e+9 = 2^31</literal> on 32-bit platforms and
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<literal>+/- 9.22e+18 = 2^63</literal> on 64-bit platforms other than
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Windows), the result is undefined, since the <type>float</type> doesn't
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have enough precision to give an exact <type>integer</type> result. No
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warning, not even a notice will be issued when this happens!
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<literal>+/- 9.22e+18 = 2^63</literal> on 64-bit platforms),
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the result is undefined, since the <type>float</type> doesn't
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have enough precision to give an exact <type>int</type> result.
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No warning, not even a notice will be issued when this happens!
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</para>
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<note>
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<para>
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NaN and Infinity will always be zero when cast to <type>int</type>.
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</para>
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</note>
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<warning>
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<para>
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Never cast an unknown fraction to <type>integer</type>, as this can
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Never cast an unknown fraction to <type>int</type>, as this can
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sometimes lead to unexpected results.
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</para>
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<title>From strings</title>
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<simpara>
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See <link linkend="language.types.string.conversion">String conversion to
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numbers</link>
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If the string is
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<link linkend="language.types.numeric-strings">numeric</link>
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or leading numeric then it will resolve to the
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corresponding integer value, otherwise it is converted to zero
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(<literal>0</literal>).
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</simpara>
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</sect3>
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<sect3 xml:id="language.types.integer.casting-from-null">
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<title>From <type>NULL</type></title>
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<simpara>
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&null; is always converted to zero (<literal>0</literal>).
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</simpara>
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</sect3>
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<caution>
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<simpara>
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The behaviour of converting to <type>integer</type> is undefined for other
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The behaviour of converting to <type>int</type> is undefined for other
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types. Do <emphasis>not</emphasis> rely on any observed behaviour, as it
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can change without notice.
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</simpara>
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