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Eleborated on syntax of constants. Moved some information that was scattered over the constant-related functions to the section on constants.

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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@49842 c90b9560-bf6c-de11-be94-00142212c4b1
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Jeroen van Wolffelaar 2001-06-19 20:36:56 +00:00
parent 62dfa44e7d
commit a085e1c8b3
2 changed files with 127 additions and 66 deletions
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50
functions/misc.xml
View file

@ -144,40 +144,18 @@ echo constant("MAXSIZE"); // same thing as the previous line
<title>Description</title>
<funcsynopsis>
<funcprototype>
<funcdef>int <function>define</function></funcdef>
<funcdef>bool <function>define</function></funcdef>
<paramdef>string <parameter>name</parameter></paramdef>
<paramdef>mixed <parameter>value</parameter></paramdef>
<paramdef>int
<paramdef>bool
<parameter><optional>case_insensitive</optional></parameter>
</paramdef>
</funcprototype>
</funcsynopsis>
<para>
Defines a named constant, which is similar to a variable except:
<itemizedlist>
<listitem>
<simpara>
Constants do not have a dollar sign '$' before them;
</simpara>
</listitem>
<listitem>
<simpara>
Constants may be accessed anywhere without regard to variable
scoping rules;
</simpara>
</listitem>
<listitem>
<simpara>
Constants may not be redefined or undefined once they have
been set; and
</simpara>
</listitem>
<listitem>
<simpara>
Constants may only evaluate to scalar values.
</simpara>
</listitem>
</itemizedlist>
Defines a named constant. See the
<link linkend="language.constants">section on constants</link>
for more details.
</para>
<para>
The name of the constant is given by <parameter>name</parameter>;
@ -186,7 +164,7 @@ echo constant("MAXSIZE"); // same thing as the previous line
<para>
The optional third parameter
<parameter>case_insensitive</parameter> is also available. If the
value <emphasis>1</emphasis> is given, then the constant will be
value <constant>TRUE</constant> is given, then the constant will be
defined case-insensitive. The default behaviour is
case-sensitive; i.e. CONSTANT and Constant represent different
values.
@ -198,12 +176,19 @@ echo constant("MAXSIZE"); // same thing as the previous line
&lt;?php
define ("CONSTANT", "Hello world.");
echo CONSTANT; // outputs "Hello world."
echo Constant; // outputs "Constant" and issues a notice.
define ("GREETING", "Hello you.",TRUE);
echo GREETING; // outputs "Hello you."
echo Greeting; // outputs "Hello you."
?&gt;
</programlisting>
</example>
</para>
<para>
<function>Define</function> returns TRUE on success and FALSE if
<function>Define</function> returns <constant>TRUE</constant>
on success and <constant>FALSE</constant> if
an error occurs.
</para>
<para>
@ -225,13 +210,14 @@ echo CONSTANT; // outputs "Hello world."
<title>Description</title>
<funcsynopsis>
<funcprototype>
<funcdef>int <function>defined</function></funcdef>
<funcdef>bool <function>defined</function></funcdef>
<paramdef>string <parameter>name</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<para>
Returns true if the named constant given by
<parameter>name</parameter> has been defined, false otherwise.
Returns <constant>TRUE</constant> if the named constant given by
<parameter>name</parameter> has been defined,
<constant>FALSE</constant> otherwise.
<example>
<title>Checking Constants</title>
<programlisting role="php">

143
language/constants.xml
View file

@ -2,13 +2,97 @@
<title>Constants</title>
<simpara>
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
<function>define</function> function, and that they cannot later be
redefined to another value.
A constant is a identifier (name) for a simple value. As the name
suggests, that value cannot change during the execution of the script
(the magic constants <constant>__FILE__</constant> and
<constant>__LINE__</constant> are the only exception). A constant
is case-sensitive by default. By convention constants are always
uppercase.
</simpara>
<simpara>
The scope of a constant is global.
</simpara>
<sect1 id="language.constants.syntax">
<title>Syntax</title>
<simpara>
You can define a constant by using the
<function>define</function>-function. Once a constant is defined,
it can never be changed or undefined.
</simpara>
<simpara>
Only scalar data (<type>boolean</type>, <type>integer</type>,
<type>double</type> and <type>string</type>) can be contained
in constants.
</simpara>
<simpara>
You can get the value of a constant by simply specifying its name.
Unlike with variables, you should <emphasis>not</emphasis> prepend
a constant with a <literal>$</literal>.
You can also use the <function>constant</function>-function, for
example if the name of the constant is variable.
Use <function>get_defined_constants</function> to get a list of
all defined constants.
</simpara>
<note>
<simpara>
Constants and (global) variables are in a different namespace.
This implies that for example <constant>TRUE</constant> and
<varname>$TRUE</varname> are generally different.
</simpara>
</note>
<simpara>
If you use an undefined constant, PHP assumes that you mean
the name of the constant itself. A
<link linkend="features.error-handling">notice</link> will be issued
when this happens. Use the <function>defined</function>-function if
you want to know if a constant is set.
</simpara>
<para>
This are the differences with variables:
<itemizedlist>
<listitem>
<simpara>
Constants do not have a dollar sign (<literal>$</literal>) before them;
</simpara>
</listitem>
<listitem>
<simpara>
Constants may be defined and accessed anywhere without regard to variable
scoping rules;
</simpara>
</listitem>
<listitem>
<simpara>
Constants may not be redefined or undefined once they have
been set; and
</simpara>
</listitem>
<listitem>
<simpara>
Constants may only evaluate to scalar values.
</simpara>
</listitem>
</itemizedlist>
</para>
<para>
<example>
<title>Defining Constants</title>
<programlisting>
&lt;?php
define("CONSTANT", "Hello world.");
echo CONSTANT; // outputs "Hello world."
echo Constant; // outputs "Constant" and issues a notice.
?&gt;
</programlisting>
</example>
</para>
</sect1>
<sect1 id="language.constants.predefined">
<title>Predefined constants</title>
<para>
The predefined constants (always available) are:
@ -63,7 +147,7 @@
<term>TRUE (case-insensitive)</term>
<listitem>
<simpara>
A true value.
A true value (see the <type>boolean</type> type).
</simpara>
</listitem>
</varlistentry>
@ -72,7 +156,16 @@
<term>FALSE (case-insensitive)</term>
<listitem>
<simpara>
A false value.
A false value (see the <type>boolean</type> type).
</simpara>
</listitem>
</varlistentry>
<varlistentry>
<term>NULL (case-insensitive)</term>
<listitem>
<simpara>
A null value (see the <type>null</type> type).
</simpara>
</listitem>
</varlistentry>
@ -114,7 +207,7 @@
<listitem>
<simpara>
Something happened which may or may not be an error. Execution
continues. Examples include using an unquoted string as a hash
continues. Examples include using an unquoted string as a array
index, or accessing a variable which has not been set.
</simpara>
</listitem>
@ -135,29 +228,10 @@
</para>
<para>
The E_* constants are typically used with the
<function>error_reporting</function> function for setting the
error reporting level. See all these constants at
<link linkend="features.error-handling">Error handling</link>.
</para>
<para>
You can define additional constants using the
<function>define</function> function.</para>
<para>
Note that these are constants, not C-style macros; only valid
scalar data may be represented by a constant.
<example>
<title>Defining Constants</title>
<programlisting>
&lt;?php
define("CONSTANT", "Hello world.");
echo CONSTANT; // outputs "Hello world."
?&gt;
</programlisting>
</example>
The <literal>E_*</literal> constants are typically used with the
<function>error_reporting</function> function for setting the
error reporting level. See all these constants at
<link linkend="features.error-handling">Error handling</link>.
<example>
<title>Using __FILE__ and __LINE__</title>
@ -170,9 +244,10 @@ function report_error($file, $line, $message) {
report_error(__FILE__,__LINE__, "Something went wrong!");
?&gt;
</programlisting>
</example></para>
</chapter>
</example>
</para>
</sect1>
</chapter>
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