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<HTML
><HEAD
><TITLE
>Constants</TITLE
><META
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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="CONSTANTS"
>Constants</A
></H1
><P
> 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
<B
CLASS="FUNCTION"
>define()</B
> function, and that they cannot later
be redefined to another value.
</P
><P
> The predefined constants (always available) are:
<P
></P
><DL
><DT
>__FILE__</DT
><DD
><P
> 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
> 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
> 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
> The name of the operating system on which the PHP parser is
executing; e.g. 'Linux'.
</P
></DD
><DT
>TRUE</DT
><DD
><P
> A true value.
</P
></DD
><DT
>FALSE</DT
><DD
><P
> A false value.
</P
></DD
><DT
>E_ERROR</DT
><DD
><P
> Denotes an error other than a parsing error from which
recovery is not possible.
</P
></DD
><DT
>E_WARNING</DT
><DD
><P
> 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
> The parser choked on invalid syntax in the script
file. Recovery is not possible.
</P
></DD
><DT
>E_NOTICE</DT
><DD
><P
> 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
></DL
>
</P
><P
> The E_* constants are typically used with the
<A
HREF="function.error-reporting.html"
><B
CLASS="FUNCTION"
>error_reporting()</B
></A
> functionfor setting the
error reporting level.
</P
><P
> You can define additional constants using the
<B
CLASS="FUNCTION"
>define()</B
> function.
</P
><P
> Note that these are constants, not C-style macros; only valid
scalar data may be represented by a constant.
<TABLE
WIDTH="100%"
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CLASS="EXAMPLE"
><TR
><TD
><DIV
CLASS="EXAMPLE"
><P
><B
>Example 5-5. Defining Constants</B
></P
><PRE
CLASS="PROGRAMLISTING"
><?php
define("CONSTANT", "Hello world.");
echo CONSTANT; // outputs "Hello world."
?>
</PRE
></DIV
></TD
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></TABLE
>
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><TR
><TD
><DIV
CLASS="EXAMPLE"
><P
><B
>Example 5-6. Using __FILE__ and __LINE__</B
></P
><PRE
CLASS="PROGRAMLISTING"
><?php
function report_error($file, $line, $message) {
echo "An error occured in $file on line $line: $message.";
}
report_error(__FILE__,__LINE__, "Something went wrong!");
?>
</PRE
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>
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