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constants.html
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constants.html
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<HTML
><HEAD
><TITLE
>Constants</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.41"><LINK
REL="HOME"
TITLE="PHP3 Manual"
HREF="manual.html"><LINK
REL="UP"
TITLE="Syntax and grammar"
HREF="lang-syntax.html"><LINK
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TITLE="Variables"
HREF="variables.html"><LINK
REL="NEXT"
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HREF="expressions.html"></HEAD
><BODY
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>PHP3 Manual</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="variables.html"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 5. Syntax and grammar</TD
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>Next</A
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><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><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
> function for 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%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
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
></TR
></TABLE
>
<TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
CLASS="EXAMPLE"
><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
></DIV
></TD
></TR
></TABLE
>
</P
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="variables.html"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="manual.html"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="expressions.html"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Variables</TD
><TD
WIDTH="34%"
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><A
HREF="lang-syntax.html"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
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>Expressions</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>