json-decode.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.json-decode" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>json_decode</refname>
  <refpurpose>Decodes a JSON string</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>mixed</type><methodname>json_decode</methodname>
   <methodparam><type>string</type><parameter>json</parameter></methodparam>
   <methodparam choice="opt"><type class="union"><type>bool</type><type>null</type></type><parameter>associative</parameter><initializer>&null;</initializer></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>depth</parameter><initializer>512</initializer></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>flags</parameter><initializer>0</initializer></methodparam>
  </methodsynopsis>
  <para>
   Takes a JSON encoded string and converts it into a PHP value.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>json</parameter></term>
     <listitem>
      <para>
       The <parameter>json</parameter> <type>string</type> being decoded.
      </para>
      <para>
       This function only works with UTF-8 encoded strings.
      </para>
      &json.implementation.superset;
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>associative</parameter></term>
     <listitem>
      <para>
       When &true;, JSON objects will be returned as
       associative &array;s; when &false;, JSON objects will be returned as &object;s.
       When &null;, JSON objects will be returned as associative &array;s or
       &object;s depending on whether <constant>JSON_OBJECT_AS_ARRAY</constant>
       is set in the <parameter>flags</parameter>.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>depth</parameter></term>
     <listitem>
      <para>
       Maximum nesting depth of the structure being decoded.
       The value must be greater than <literal>0</literal>,
       and less than or equal to <literal>2147483647</literal>.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>flags</parameter></term>
     <listitem>
      <para>
       Bitmask of
       <constant>JSON_BIGINT_AS_STRING</constant>,
       <constant>JSON_INVALID_UTF8_IGNORE</constant>,
       <constant>JSON_INVALID_UTF8_SUBSTITUTE</constant>,
       <constant>JSON_OBJECT_AS_ARRAY</constant>,
       <constant>JSON_THROW_ON_ERROR</constant>.
       The behaviour of these constants is described on the
       <link linkend="json.constants">JSON constants</link> page.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns the value encoded in <parameter>json</parameter> as an appropriate
   PHP type. Unquoted values <literal>true</literal>, <literal>false</literal>
   and <literal>null</literal> are returned as &true;,
   &false; and &null; respectively. &null; is returned if the
   <parameter>json</parameter> cannot be decoded or if the encoded data is
   deeper than the nesting limit.
  </para>
 </refsect1>

 <refsect1 role="errors">
  &reftitle.errors;
  <para>
   If <parameter>depth</parameter> is outside the allowed range,
   a <classname>ValueError</classname> is thrown as of PHP 8.0.0,
   while previously, an error of level <constant>E_WARNING</constant> was raised.
  </para>
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <para>
   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>&Version;</entry>
       <entry>&Description;</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>7.3.0</entry>
       <entry>
        <constant>JSON_THROW_ON_ERROR</constant>
        <parameter>flags</parameter> was added.
       </entry>
      </row>
      <row>
       <entry>7.2.0</entry>
       <entry>
        <parameter>associative</parameter> is nullable now.
       </entry>
      </row>
      <row>
       <entry>7.2.0</entry>
       <entry>
        <constant>JSON_INVALID_UTF8_IGNORE</constant>, and
        <constant>JSON_INVALID_UTF8_SUBSTITUTE</constant>
        <parameter>flags</parameter> were added.
       </entry>
      </row>
      <row>
       <entry>7.1.0</entry>
       <entry>
        An empty JSON key ("") can be encoded to the empty object property
        instead of using a key with value <literal>_empty_</literal>.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>json_decode</function> examples</title>
    <programlisting role="php">
<![CDATA[
<?php
$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}';

var_dump(json_decode($json));
var_dump(json_decode($json, true));

?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
object(stdClass)#1 (5) {
    ["a"] => int(1)
    ["b"] => int(2)
    ["c"] => int(3)
    ["d"] => int(4)
    ["e"] => int(5)
}

array(5) {
    ["a"] => int(1)
    ["b"] => int(2)
    ["c"] => int(3)
    ["d"] => int(4)
    ["e"] => int(5)
}
]]>
    </screen>
   </example>
   <example>
    <title>Accessing invalid object properties</title>
    <simpara>
     Accessing elements within an object that contain characters not
     permitted under PHP's naming convention (e.g. the hyphen) can be
     accomplished by encapsulating the element name within braces and the apostrophe.
    </simpara>
    <programlisting role="php">
<![CDATA[
<?php

$json = '{"foo-bar": 12345}';

$obj = json_decode($json);
print $obj->{'foo-bar'}; // 12345

?>
]]>
    </programlisting>
   </example>
   <example>
    <title>common mistakes using <function>json_decode</function></title>
    <programlisting role="php">
<![CDATA[
<?php

// the following strings are valid JavaScript but not valid JSON

// the name and value must be enclosed in double quotes
// single quotes are not valid 
$bad_json = "{ 'bar': 'baz' }";
json_decode($bad_json); // null

// the name must be enclosed in double quotes
$bad_json = '{ bar: "baz" }';
json_decode($bad_json); // null

// trailing commas are not allowed
$bad_json = '{ bar: "baz", }';
json_decode($bad_json); // null

?>
]]>
    </programlisting>
   </example>
   <example>
    <title><parameter>depth</parameter> errors</title>
    <programlisting role="php">
<![CDATA[
<?php
// Encode some data with a maximum depth  of 4 (array -> array -> array -> string)
$json = json_encode(
    array(
        1 => array(
            'English' => array(
                'One',
                'January'
            ),
            'French' => array(
                'Une',
                'Janvier'
            )
        )
    )
);

// Show the errors for different depths.
var_dump(json_decode($json, true, 4));
echo 'Last error: ', json_last_error_msg(), PHP_EOL, PHP_EOL;

var_dump(json_decode($json, true, 3));
echo 'Last error: ', json_last_error_msg(), PHP_EOL, PHP_EOL;
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
array(1) {
  [1]=>
  array(2) {
    ["English"]=>
    array(2) {
      [0]=>
      string(3) "One"
      [1]=>
      string(7) "January"
    }
    ["French"]=>
    array(2) {
      [0]=>
      string(3) "Une"
      [1]=>
      string(7) "Janvier"
    }
  }
}
Last error: No error

NULL
Last error: Maximum stack depth exceeded
]]>
    </screen>
   </example>
   <example>
    <title><function>json_decode</function> of large integers</title>
    <programlisting role="php">
<![CDATA[
<?php
$json = '{"number": 12345678901234567890}';

var_dump(json_decode($json));
var_dump(json_decode($json, false, 512, JSON_BIGINT_AS_STRING));

?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
object(stdClass)#1 (1) {
  ["number"]=>
  float(1.2345678901235E+19)
}
object(stdClass)#1 (1) {
  ["number"]=>
  string(20) "12345678901234567890"
}
]]>
    </screen>
   </example>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <note>
   <para>
    The JSON spec is not JavaScript, but a subset of JavaScript.
   </para>
  </note>
  <note>
   <para>
    In the event of a failure to decode, <function>json_last_error</function>
    can be used to determine the exact nature of the error.
   </para>
  </note>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>json_encode</function></member>
    <member><function>json_last_error</function></member>
    <member><function>json_last_error_msg</function></member>
   </simplelist>
  </para>
 </refsect1>
</refentry>
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