basics.xml

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<sect1 xml:id="language.errors.basics" xmlns="http://docbook.org/ns/docbook">
 <title>Basics</title>

 <para>
  PHP reports errors in response to a number of internal error conditions.
  These may be used to signal a number of different conditions, and can be
  displayed and/or logged as required.
 </para>

 <para>
  Every error that PHP generates includes a type. A
  <link linkend="errorfunc.constants">list of these error types</link> is available,
  along with a short description of their behaviour and how they can be
  caused.
 </para>

 <sect2 xml:id="language.errors.basics.handling">
  <title>Handling errors with PHP</title>

  <para>
   If no error handler is set, then PHP will handle any errors that occur
   according to its configuration. Which errors are reported and which are
   ignored is controlled by the
   <link linkend="ini.error-reporting"><parameter>error_reporting</parameter></link>
   php.ini directive, or at runtime by calling
   <function>error_reporting</function>. It is strongly recommended that the
   configuration directive be set, however, as some errors can occur before
   execution of your script begins.
  </para>

  <para>
   In a development environment, you should always set
   <link linkend="ini.error-reporting"><parameter>error_reporting</parameter></link>
   to <constant>E_ALL</constant>, as you need to be aware of and fix the
   issues raised by PHP. In production, you may wish to set this to a less
   verbose level such as
   <code>E_ALL &amp; ~E_NOTICE &amp; ~E_DEPRECATED</code>, but
   in many cases <constant>E_ALL</constant> is also appropriate, as it may
   provide early warning of potential issues.
  </para>

  <para>
   What PHP does with these errors depends on two further php.ini directives.
   <link linkend="ini.display-errors"><parameter>display_errors</parameter></link>
   controls whether the error is shown as part of the script's output. This
   should always be disabled in a production environment, as it can include
   confidential information such as database passwords, but is often useful to
   enable in development, as it ensures immediate reporting of issues.
  </para>

  <para>
   In addition to displaying errors, PHP can log errors when the
   <link linkend="ini.log-errors"><parameter>log_errors</parameter></link>
   directive is enabled. This will log any errors to the file or syslog
   defined by
   <link linkend="ini.error-log"><parameter>error_log</parameter></link>. This
   can be extremely useful in a production environment, as you can log errors
   that occur and then generate reports based on those errors.
  </para>
 </sect2>

 <sect2 xml:id="language.errors.basics.user">
  <title>User error handlers</title>

  <para>
   If PHP's default error handling is inadequate, you can also handle many
   types of error with your own custom error handler by installing it with
   <function>set_error_handler</function>. While some error types cannot be
   handled this way, those that can be handled can then be handled in the way
   that your script sees fit: for example, this can be used to show a custom
   error page to the user and then report more directly than via a log, such
   as by sending an e-mail.
  </para>
 </sect2>
</sect1>
 
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