变量

基础
预定义变量
变量范围
可变变量
来自 PHP 之外的变量

用户评论:

[#1] Kubo2 [2015-03-22 11:10:20]

Note that if you use runtime variable name recognition in your code, you are able to use any string as a variable name. Consider following code:

<?php $varName = 'foo with bar'; ${'foo with bar'} = 42; // will output int(42) var_dump($$varName); ?>

This can be useful for example when accessing a property of an object constructed from JSON:

<?php $composerJson = json_decode(file_get_contents(__DIR__ . '/composer.json')); // would output sth. similar to: object(stdClass)#... var_dump( $composerJson->{'require-dev'} ); ?>

[#2] justgook at gmail dot com [2010-08-03 13:38:14]

I found interstate solution to work with arrays

<?php $vars['product']['price']=11; $aa='product'; $bb='price'; echo $vars{$aa}{$bb}; //prints 11 ?>

[#3] dimitrov dot adrian at gmail dot com [2010-07-29 06:52:25]

This is mine type casting lib, that is very useful for me.

<?php function CAST_TO_INT($var, $min = FALSE, $max = FALSE) { $var = is_int($var) ? $var : (int)(is_scalar($var) ? $var : 0); if ($min !== FALSE && $var < $min) return $min; elseif($max !== FALSE && $var > $max) return $max; return $var; } function CAST_TO_FLOAT($var, $min = FALSE, $max = FALSE) { $var = is_float($var) ? $var : (float)(is_scalar($var) ? $var : 0); if ($min !== FALSE && $var < $min) return $min; elseif($max !== FALSE && $var > $max) return $max; return $var; } function CAST_TO_BOOL($var) { return (bool)(is_bool($var) ? $var : is_scalar($var) ? $var : FALSE); } function CAST_TO_STRING($var, $length = FALSE) { if ($length !== FALSE && is_int($length) && $length > 0) return substr(trim(is_string($var) ? $var : (is_scalar($var) ? $var : '')), 0, $length); return trim( is_string($var) ? $var : (is_scalar($var) ? $var : '')); } function CAST_TO_ARRAY($var) { return is_array($var) ? $var : is_scalar($var) && $var ? array($var) : is_object($var) ? (array)$var : array(); } function CAST_TO_OBJECT($var) { return is_object($var) ? $var : is_scalar($var) && $var ? (object)$var : is_array($var) ? (object)$var : (object)NULL; } ?>

[#4] Anonymous [2008-07-20 06:25:28]

[EDIT by danbrown AT php DOT net: The function provided by this author will give you all defined variables at runtime. It was originally written by (john DOT t DOT gold AT gmail DOT com), but contained some errors that were corrected in subsequent posts by (ned AT wgtech DOT com) and (taliesin AT gmail DOT com).]

<?php echo '<table border=1><tr> <th>variable</th> <th>value</th> </tr>'; foreach( get_defined_vars() as $key => $value) { if (is_array ($value) ) { echo '<tr><td>$'.$key .'</td><td>'; if ( sizeof($value)>0 ) { echo '"<table border=1><tr> <th>key</th> <th>value</th> </tr>'; foreach ($value as $skey => $svalue) { echo '<tr><td>[' . $skey .']</td><td>"'. $svalue .'"</td></tr>'; } echo '</table>"'; } else { echo 'EMPTY'; } echo '</td></tr>'; } else { echo '<tr><td>$' . $key .'</td><td>"'. $value .'"</td></tr>'; } } echo '</table>'; ?>

[#5] jsb17 at cornell dot edu [2007-02-20 08:48:25]

As an addendum to David's 10-Nov-2005 posting, remember that curly braces literally mean "evaluate what's inside the curly braces" so, you can squeeze the variable variable creation into one line, like this:

<?php ${"title_default_" . $title} = "selected"; ?>

and then, for example:

<?php $title_select = <<<END <select name="title"> <option>Select</option> <option $title_default_Mr value="Mr">Mr</option> <option $title_default_Ms value="Ms">Ms</option> <option $title_default_Mrs value="Mrs">Mrs</option> <option $title_default_Dr value="Dr">Dr</option> </select> END; ?>

[#6] Mike at ImmortalSoFar dot com [2005-11-25 14:03:14]

References and "return" can be flakey:

<?php // This only returns a copy, despite the dereferencing in the function definition function &GetLogin () { return $_SESSION['Login']; } // This gives a syntax error function &GetLogin () { return &$_SESSION['Login']; } // This works function &GetLogin () { $ret = &$_SESSION['Login']; return $ret; } ?>

[#7] david at removethisbit dot futuresbright dot com [2005-11-10 01:25:23]

When using variable variables this is invalid:

<?php $my_variable_{$type}_name = true; ?>

to get around this do something like:

<?php $n="my_variable_{$type}_name"; ${$n} = true; ?>

(or $$n - I tend to use curly brackets out of habit as it helps t reduce bugs ...)

[#8] Chris Hester [2005-08-31 05:09:52]

Variables can also be assigned together.

<?php $a = $b = $c = 1; echo $a.$b.$c; ?>

This outputs 111.

[#9] josh at PraxisStudios dot com [2005-05-17 13:06:22]

As with echo, you can define a variable like this:

<?php $text = <<<END <table> <tr> <td> $outputdata </td> </tr> </table> END; ?>

The closing END; must be on a line by itself (no whitespace).

[EDIT by danbrown AT php DOT net: This note illustrates HEREDOC syntax. For more information on this and similar features, please read the "Strings" section of the manual here: http://www.php.net/manual/en/language.types.string.php ]

[#10] Carel Solomon [2005-01-07 03:02:21]

You can also construct a variable name by concatenating two different variables, such as:

<?php $arg = "foo"; $val = "bar"; //${$arg$val} = "in valid"; // Invalid ${$arg . $val} = "working"; echo $foobar; // "working"; //echo $arg$val; // Invalid //echo ${$arg$val}; // Invalid echo ${$arg . $val}; // "working" ?>

Carel

[#11] raja shahed at christine nothdurfter dot com [2004-05-25 10:58:15]

<?php error_reporting(E_ALL); $name = "Christine_Nothdurfter"; // not Christine Nothdurfter // you are not allowed to leave a space inside a variable name ;) $$name = "'s students of Tyrolean language "; print " $name{$$name}<br>"; print "$name$Christine_Nothdurfter"; // same ?>

[#12] webmaster at daersys dot net [2004-01-20 08:15:00]

You don't necessarily have to escape the dollar-sign before a variable if you want to output its name.

You can use single quotes instead of double quotes, too.

For instance:

<?php $var = "test"; echo "$var"; // Will output the string "test" echo "\$var"; // Will output the string "$var" echo '$var'; // Will do the exact same thing as the previous line ?>

Why?
Well, the reason for this is that the PHP Parser will not attempt to parse strings encapsulated in single quotes (as opposed to strings within double quotes) and therefore outputs exactly what it's being fed with :)

To output the value of a variable within a single-quote-encapsulated string you'll have to use something along the lines of the following code:

<?php $var = 'test'; echo '$var = "' . $var . '"'; ?>

HTH
- Daerion

变量

Table of Contents

用户评论: