doc-en/reference/json/functions/json-validate.xml

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<refentry xml:id="function.json-validate" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>json_validate</refname>
  <refpurpose>Checks if a string contains valid JSON</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>bool</type><methodname>json_validate</methodname>
   <methodparam><type>string</type><parameter>json</parameter></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>
   Returns whether the given &string; is syntactically valid JSON.
   If <function>json_validate</function> returns &true;, <function>json_decode</function>
   will successfully decode the given string when using the same
   <parameter>depth</parameter> and <parameter>flags</parameter>.
  </para>
  <para>
   If <function>json_validate</function> returns &false;, the cause
   can be retrieved using <function>json_last_error</function> and
   <function>json_last_error_msg</function>.
  </para>
  <para>
   <function>json_validate</function> uses less memory than
   <function>json_decode</function> if the decoded JSON payload is
   not used, because it does not need to build the array or
   object structure containing the payload.
  </para>
  <caution>
   <para>
    Calling <function>json_validate</function> immediately before
    <function>json_decode</function> will unnecessarily parse the string
    twice, as <function>json_decode</function> implicitly performs
    validation during decoding.
   </para>
   <para>
    <function>json_validate</function> should therefore only be used
    if the decode JSON payload is not immediately used and knowing whether
    the string contains valid JSON is needed.
   </para>
  </caution>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>json</parameter></term>
     <listitem>
      <para>
       The string to validate.
      </para>
      <para>
       This function only works with UTF-8 encoded strings.
      </para>
      &json.implementation.superset;
     </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>
       Currently only
       <constant>JSON_INVALID_UTF8_IGNORE</constant>
       is accepted.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns &true; if the given string is syntactically valid JSON, otherwise
   returns &false;.
  </para>
 </refsect1>

 <refsect1 role="errors">
  &reftitle.errors;
  <para>
   If <parameter>depth</parameter> is outside the allowed range,
   a <classname>ValueError</classname> is thrown.
  </para>
  <para>
   If <parameter>flags</parameter> is not a valid flag,
   a <classname>ValueError</classname> is thrown.
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>json_validate</function> examples</title>
    <programlisting role="php">
<![CDATA[
<?php
var_dump(json_validate('{ "test": { "foo": "bar" } }'));
var_dump(json_validate('{ "": "": "" } }'));
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
bool(true)
bool(false)
]]>
    </screen>
   </example>
  </para>
 </refsect1>

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