Sophie: php-manual-en-4.3.0-2mdk noarch

php-manual-en-4.3.0-2mdk.noarch.rpm

<HTML
><HEAD
><TITLE
>Constants</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
REL="HOME"
TITLE="PHP Manual"
HREF="index.html"><LINK
REL="UP"
TITLE="Language Reference"
HREF="langref.html"><LINK
REL="PREVIOUS"
TITLE="Variables from outside PHP"
HREF="language.variables.external.html"><LINK
REL="NEXT"
TITLE="Predefined constants"
HREF="language.constants.predefined.html"><META
HTTP-EQUIV="Content-type"
CONTENT="text/html; charset=ISO-8859-1"></HEAD
><BODY
CLASS="chapter"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>PHP Manual</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="language.variables.external.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
></TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="language.constants.predefined.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="chapter"
><H1
><A
NAME="language.constants"
>Chapter 9. Constants</A
></H1
><DIV
CLASS="TOC"
><DL
><DT
><B
>Table of Contents</B
></DT
><DT
><A
HREF="language.constants.html#language.constants.syntax"
>Syntax</A
></DT
><DT
><A
HREF="language.constants.predefined.html"
>Predefined constants</A
></DT
></DL
></DIV
><P
>&#13;   A constant is a identifier (name) for a simple value. As the name
   suggests, that value cannot change during the execution of the
   script (except the <A
HREF="language.constants.predefined.html"
>&#13;   magic constants</A
> which aren't actually constants).
   A constant is case-sensitive by default. By convention constant 
   identifiers are always uppercase.
  </P
><P
>&#13;   The name of a constant follows the same rules as any label in PHP. A 
   valid constant name starts with a letter or underscore, followed
   by any number of letters, numbers, or underscores. As a regular
   expression, it would be expressed thus:
   <TT
CLASS="literal"
>[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*</TT
>

   
  </P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Note: </B
>
    For our purposes here, a letter is a-z, A-Z, and the ASCII
    characters from 127 through 255 (0x7f-0xff).
   </P
></BLOCKQUOTE
></DIV
><P
>&#13;   The scope of a constant is global--you can access it anywhere in
   your script without regard to scope.
  </P
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="language.constants.syntax"
></A
>Syntax</H1
><P
>&#13;    You can define a constant by using the 
    <A
HREF="function.define.html"
><B
CLASS="function"
>define()</B
></A
>-function. Once a constant is defined,
    it can never be changed or undefined.
   </P
><P
>&#13;    Only scalar data (<A
HREF="language.types.boolean.html"
><B
CLASS="type"
>boolean</B
></A
>, <A
HREF="language.types.integer.html"
><B
CLASS="type"
>integer</B
></A
>, 
    <A
HREF="language.types.float.html"
><B
CLASS="type"
>float</B
></A
> and <A
HREF="language.types.string.html"
><B
CLASS="type"
>string</B
></A
>) can be contained 
    in constants.
   </P
><P
>&#13;    You can get the value of a constant by simply specifying its name.
    Unlike with variables, you should <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>not</I
></SPAN
> prepend
    a constant with a <TT
CLASS="literal"
>$</TT
>.
    You can also use the function <A
HREF="function.constant.html"
><B
CLASS="function"
>constant()</B
></A
>, to
    read a constant's value, if you are to obtain the constant's name
    dynamically. 
    Use <A
HREF="function.get-defined-constants.html"
><B
CLASS="function"
>get_defined_constants()</B
></A
> to get a list of 
    all defined constants.
   </P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Note: </B
>
     Constants and (global) variables are in a different namespace. 
     This implies that for example <TT
CLASS="constant"
><B
>TRUE</B
></TT
> and 
     <TT
CLASS="varname"
>$TRUE</TT
> are generally different.
    </P
></BLOCKQUOTE
></DIV
><P
>&#13;    If you use an undefined constant, PHP assumes that you mean
    the name of the constant itself. A 
    <A
HREF="ref.errorfunc.html"
>notice</A
> will be issued
    when this happens. Use the <A
HREF="function.defined.html"
><B
CLASS="function"
>defined()</B
></A
>-function if 
    you want to know if a constant is set.
   </P
><P
>&#13;    These are the differences between constants and variables:
    <P
></P
><UL
><LI
><P
>&#13;       Constants do not have a dollar sign (<TT
CLASS="literal"
>$</TT
>)
       before them;
      </P
></LI
><LI
><P
>&#13;       Constants may only be defined using the
       <A
HREF="function.define.html"
><B
CLASS="function"
>define()</B
></A
> function, not by simple assignment;
      </P
></LI
><LI
><P
>&#13;       Constants may be defined and accessed anywhere without regard
       to variable scoping rules;
      </P
></LI
><LI
><P
>&#13;       Constants may not be redefined or undefined once they have been
       set; and
      </P
></LI
><LI
><P
>&#13;       Constants may only evaluate to scalar values.
       </P
></LI
></UL
>
   </P
><P
>&#13;    <TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
CLASS="EXAMPLE"
><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN4314"
></A
><P
><B
>Example 9-1. Defining Constants</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><PRE
CLASS="php"
>&#60;?php
define("CONSTANT", "Hello world.");
echo CONSTANT; // outputs "Hello world."
echo Constant; // outputs "Constant" and issues a notice.
?&#62;</PRE
></TD
></TR
></TABLE
></DIV
></TD
></TR
></TABLE
>

   </P
></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="language.variables.external.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="language.constants.predefined.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Variables from outside PHP</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="langref.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Predefined constants</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>