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><H1
><A
NAME="language.constants"
>Chapter 8. Constants</A
></H1
><P
>&#13;   PHP defines several constants and provides a mechanism for defining
   more at run-time. Constants are much like variables, save for the
   two facts that constants must be defined using the
   <A
HREF="function.define.html"
><B
CLASS="function"
>define()</B
></A
> function, and that they cannot later be
   redefined to another value.
  </P
><P
>&#13;   The predefined constants (always available) are:

   <P
></P
><DIV
CLASS="variablelist"
><DL
><DT
>__FILE__</DT
><DD
><P
>&#13;       The name of the script file presently being parsed. If used
       within a file which has been included or required, then the
       name of the included file is given, and not the name of the
       parent file.
      </P
></DD
><DT
>__LINE__</DT
><DD
><P
>&#13;       The number of the line within the current script file which is
       being parsed. If used within a file which has been included or
       required, then the position within the included file is given.
      </P
></DD
><DT
>PHP_VERSION</DT
><DD
><P
>&#13;       The string representation of the version of the PHP parser
       presently in use; e.g. '3.0.8-dev'.
      </P
></DD
><DT
>PHP_OS</DT
><DD
><P
>&#13;       The name of the operating system on which the PHP parser is
       executing; e.g. 'Linux'.
      </P
></DD
><DT
>TRUE</DT
><DD
><P
>&#13;       A true value.
      </P
></DD
><DT
>FALSE</DT
><DD
><P
>&#13;       A false value.
      </P
></DD
><DT
>E_ERROR</DT
><DD
><P
>&#13;       Denotes an error other than a parsing error from which
       recovery is not possible. 
      </P
></DD
><DT
>E_WARNING</DT
><DD
><P
>&#13;       Denotes a condition where PHP knows something is wrong, but
       will continue anyway; these can be caught by the script
       itself. An example would be an invalid regexp in
       <A
HREF="function.ereg.html"
><B
CLASS="function"
>ereg()</B
></A
>.
      </P
></DD
><DT
>E_PARSE</DT
><DD
><P
>&#13;       The parser choked on invalid syntax in the script
       file. Recovery is not possible.
      </P
></DD
><DT
>E_NOTICE</DT
><DD
><P
>&#13;       Something happened which may or may not be an error. Execution
       continues. Examples include using an unquoted string as a hash
       index, or accessing a variable which has not been set.
      </P
></DD
><DT
>E_ALL</DT
><DD
><P
>&#13;       All of the E_* constants rolled into one. If used with
       <A
HREF="function.error-reporting.html"
><B
CLASS="function"
>error_reporting()</B
></A
>, will cause any and all
       problems noticed by PHP to be reported.
      </P
></DD
></DL
></DIV
>
  </P
><P
>&#13;	  The E_* constants are typically used with the
	  <A
HREF="function.error-reporting.html"
><B
CLASS="function"
>error_reporting()</B
></A
> function for setting the
	  error reporting level. See all these constants at
	  <A
HREF="features.error-handling.html"
>Error handling</A
>.
	 </P
><P
>&#13;    You can define additional constants using the
    <A
HREF="function.define.html"
><B
CLASS="function"
>define()</B
></A
> function.</P
><P
>&#13;	Note that these are constants, not C-style macros; only valid
	scalar data may be represented by a constant.

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><A
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></A
><P
><B
>Example 8-1. Defining Constants</B
></P
><TABLE
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><TR
><TD
><PRE
CLASS="programlisting"
>&#13;&#60;?php
define("CONSTANT", "Hello world.");
echo CONSTANT; // outputs "Hello world."
?&#62;
     </PRE
></TD
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><B
>Example 8-2. Using __FILE__ and __LINE__</B
></P
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><TD
><PRE
CLASS="programlisting"
>&#13;&#60;?php
function report_error($file, $line, $message) {
    echo "An error occured in $file on line $line: $message.";
}

report_error(__FILE__,__LINE__, "Something went wrong!");
?&#62;
     </PRE
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