©
本文档使用 PHP中文网手册 发布
(PHP 4 >= 4.2.0, PHP 5, PHP 7)
var_export — 输出或返回一个变量的字符串表示
$expression
[, bool $return
] )此函数返回关于传递给该函数的变量的结构信息,它和 var_dump() 类似,不同的是其返回的表示是合法的 PHP 代码。
您可以通过将函数的第二个参数设置为
TRUE
,从而返回变量的表示。
比较 var_export() 和 var_dump() .
<pre>
<?php
$a = array ( 1 , 2 , array ( "a" , "b" , "c" ));
var_export ( $a );
$b = 3.1 ;
$v = var_export ( $b , TRUE );
echo $v ;
?>
</pre>
[#1] cpmcgrat()uci ! edu [2015-07-27 22:45:52]
When trying to use __set_state() to rebuild a huge, tricky class use the following:
class Foo
{
public $a;
public $b;
public $c;
public $d;
public $e;
public $f;
public $g;
public $h;
public $i;
public function __set_state($array)
{
$obj = new ArrayConfig;
foreach($array as $k => $v) {
eval('$obj->'.$k.' = '.$v.';');
}
return $obj;
}
}
This will return a reconstructed version of the class without having to manually type each individual object in the class manually (as shown in the __set_state() example)
[#2] dan at coders dot co dot nz [2014-01-10 14:11:54]
I found that my complex type was exporting with
stdClass::__set_state()
in places. Not only was that strange and messy, it cannot be eval()-ed back in at all. Fatal error. Doh!
However a quick string-replace tidy-up of the result rendered it valid again.
$macro = var_export($data, TRUE);
$macro = str_replace("stdClass::__set_state", "(object)", $macro);
$macro = '$data = ' . $macro . ';';
And now the string I output *can* be evaluated back in again.
[#3] wyattstorch42 at outlook dot com [2013-12-22 22:11:40]
If you call var_export() on an instance of stdClass, it attempts to export it using ::__set_state(), which, for some reason, is not implemented in stdClass.
However, casting an associative array to an object usually produces the same effect (at least, it does in my case). So I wrote an improved_var_export() function to convert instances of stdClass to (object) array () calls. If you choose to export objects of any other class, I'd advise you to implement ::__set_state().
<?php
function improved_var_export ($variable, $return = false) {
if ($variable instanceof stdClass) {
$result = '(object) '.improved_var_export(get_object_vars($variable), true);
} else if (is_array($variable)) {
$array = array ();
foreach ($variable as $key => $value) {
$array[] = var_export($key, true).' => '.improved_var_export($value, true);
}
$result = 'array ('.implode(', ', $array).')';
} else {
$result = var_export($variable, true);
}
if (!$return) {
print $result;
return null;
} else {
return $result;
}
}
// Example usage:
$obj = new stdClass;
$obj->test = 'abc';
$obj->other = 6.2;
$obj->arr = array (1, 2, 3);
improved_var_export((object) array (
'prop1' => true,
'prop2' => $obj,
'assocArray' => array (
'apple' => 'good',
'orange' => 'great'
)
));
?>
Note: This function spits out a single line of code, which is useful to save in a cache file to include/eval. It isn't formatted for readability. If you want to print a readable version for debugging purposes, then I would suggest print_r() or var_dump().
[#4] chudinov at yahoo dot com [2013-11-29 09:55:30]
Looks like since version 5.4.22 var_export uses the serialize_precision ini setting, rather than the precision one used for normal output of floating-point numbers.
As a consequence since version 5.4.22 for example var_export(1.1) will output 1.1000000000000001 (17 is default precision value) and not 1.1 as before.
<?php
//ouput 1.1000000000000001
var_export(1.1)
?>
[#5] NitPicker [2013-07-10 16:33:55]
When it comes to HTML output (as discussed below), it's all fun and games until someone pokes their eye out with a "<".
Surround it with "<pre>", but do remember to wrap it in htmlspecialchars() as well.
[#6] sergei dot solomonov at gmail dot com [2012-10-04 16:00:22]
<?php
$closure = function(){};
var_export($closure);
// output: Closure::__set_state(array())
?>
[#7] kexianbin at diyism dot com [2012-09-16 02:33:56]
to use my_var_export(), it is as beautiful as var_export() and as could deal with recursive reference as print_r():
<?php
function my_var_export($var, $is_str=false)
{$rtn=preg_replace(array('/Array\s+\(/', '/\[(\d+)\] => (.*)\n/', '/\[([^\d].*)\] => (.*)\n/'), array('array (', '\1 => \'\2\''."\n", '\'\1\' => \'\2\''."\n"), substr(print_r($var, true), 0, -1));
$rtn=strtr($rtn, array("=> 'array ('"=>'=> array ('));
$rtn=strtr($rtn, array(")\n\n"=>")\n"));
$rtn=strtr($rtn, array("'\n"=>"',\n", ")\n"=>"),\n"));
$rtn=preg_replace(array('/\n +/e'), array('strtr(\'\0\', array(\' \'=>\' \'))'), $rtn);
$rtn=strtr($rtn, array(" Object',"=>" Object'<-"));
if ($is_str)
{return $rtn;
}
else
{echo $rtn;
}
}
?>
[#8] jodybrabec at gmail dot com [2012-03-28 05:52:43]
WORKAROUND for error "Nesting level too deep - recursive dependency":
ob_start();
var_dump($GLOBALS);
$dataDump = ob_get_clean();
echo $dataDump;
[#9] Anonymous [2011-11-11 09:13:54]
There is an even simpler way to have clean output from var_export and print_r in html pages:
<?php
function pretty_var($myArray)
{
echo "<pre>";
var_export($myArray);
echo "</pre>";
}
?>
[#10] laszlo dot heredy at gmail dot com [2010-10-06 13:57:56]
Try this function instead of var_export($GLOBALS) or var_dump($GLOBALS) when all you want to know is the values of the variables you set on the current page.
<?php
function globalvars(){
$result=array();
$skip=array('GLOBALS','_ENV','HTTP_ENV_VARS',
'_POST','HTTP_POST_VARS','_GET',
'HTTP_GET_VARS',
'_COOKIE',
'HTTP_COOKIE_VARS','_SERVER',
'HTTP_SERVER_VARS',
'_FILES','HTTP_POST_FILES',
'_REQUEST','HTTP_SESSION_VARS',
'_SESSION');
foreach($GLOBALS as $k=>$v)
if(!in_array($k,$skip))
$result[$k]=$v;
return $result;
}//functionglobalvars
var_export(globalvars());
?>
[#11] 4n4jmza02 at sneakemail dot com [2010-06-17 16:50:41]
I learned the hard way that if var_export encounters a resource handle it exports it as "NULL", even if it is a valid handle. The documentation states that a handle cannot be exported, but it does not describe what happens if you try to do so anyway.
I had been using var_export in some debugging code while tracing a problem with a resource handle not being generated and ended up thinking that null handles were still being generated long after the problem had been fixed.
[#12] john dot risken at gmail dot com [2010-01-16 15:53:16]
I didn't see this simple little item anywhere in the user notes. Maybe I'm blind!
Anyway, var_export and print_r both use spaces and carriage returns for formatting. Sent to an html page, most of the formatting is lost. This simple function prints a nicely formatted array to an html screen:
<?php
function pretty_var($myArray){
print str_replace(array("\n"," "),array("<br>"," "), var_export($myArray,true))."<br>";
}
?>
[#13] rarioj at gmail dot com [2009-10-28 22:43:49]
NOTE: If an object Foo has __set_state() method, but if that object contains another object Bar with no __set_state() method implemented, the resulting PHP expression will not be eval()-able.
This is an example (object Test that contains an instance of Exception).
<?php
class Test
{
public $one;
public $two;
public function __construct($one, $two)
{
$this->one = $one;
$this->two = $two;
}
public static function __set_state(array $array)
{
return new self($array['one'], $array['two']);
}
}
$test = new Test('one', new Exception('test'));
$string = var_export($test, true);
eval('$test2 = '.$string.';'); // Fatal error: Call to undefined method Exception::__set_state
?>
So avoid using var_export() on a complex array/object that contains other objects. Instead, use serialize() and unserialize() functions.
<?php
$string = 'unserialize('.var_export(serialize($test), true).')';
eval('$test2 = '.$string.';');
var_dump($test == $test2); // bool(true)
?>
[#14] ravenswd at gmail dot com [2009-07-07 10:32:07]
(This replaces my note of 3-July-2009. The original version produced no output if a variable contained an empty array, or an array consisting only of empty arrays. For example, $bigarray['x'] = array(); Also, I have added a second version of the function.)
The output can be difficult to decipher when looking at an array with many levels and many elements on each level. For example:
<?php
print ('$bigarray = ' . var_export($bigarray, true) . "\n");
?>
will return:
$bigarray = array(
... (500 lines skipped) ...
'mod' => 'charlie',
Whereas the routine below can be called with:
<?php
recursive_print ('$bigarray', $bigarray);
?>
and it will return:
$bigarray = array()
... (500 lines skipped) ...
$bigarray['foo']['bar']['0']['somethingelse']['mod'] = 'charlie'
Here's the function:
<?php
function recursive_print ($varname, $varval) {
if (! is_array($varval)):
print $varname . ' = ' . $varval . "<br>\n";
else:
print $varname . " = array()<br>\n";
foreach ($varval as $key => $val):
recursive_print ($varname . "['" . $key . "']", $val);
endforeach;
endif;
}
?>
For those who want a version that produces valid PHP code, use this version:
<?php
function recursive_print ($varname, $varval) {
if (! is_array($varval)):
print $varname . ' = ' . var_export($varval, true) . ";<br>\n";
else:
print $varname . " = array();<br>\n";
foreach ($varval as $key => $val):
recursive_print ($varname . "[" . var_export($key, true) . "]", $val);
endforeach;
endif;
}
?>
If your output is to a text file and not an HTML page, remove the <br>s.
[#15] ravenswd at gmail dot com [2009-07-03 05:21:15]
The output can be difficult to decipher when looking at an array with many levels and many elements on each level. For example:
<?php
print ('$bigarray = ' . var_export($bigarray, true) . "\n");
?>
will return:
$bigarray = array(
... (500 lines skipped) ...
'mod' => 'charlie',
Whereas the routine below can be called with:
<?php
recursive_print ('$bigarray', $bigarray);
?>
and it will return:
$bigarray['firstelement'] = 'something'
... (500 lines skipped) ...
$bigarray['foo']['bar']['0']['somethingelse']['mod'] = 'charlie'
Here's the function:
<?php
function recursive_print ($varname, $varval) {
if (! is_array($varval)):
print $varname . ' = ' . $varval . "<br>\n";
else:
foreach ($varval as $key => $val):
recursive_print ($varname . "['" . $key . "']", $val);
endforeach;
endif;
}
?>
[#16] cmusicfan (at) gmail (daught) com [2009-06-11 21:19:21]
Caution! var_export will add a backslash to single quotes (').
You may want to use stripslashes() to remove the mysteriously added backslashes.
[#17] stangelanda at arrowquick dot com [2007-06-29 16:20:48]
I have been looking for the best method to store data in cache files.
First, I've identified two limitations of var_export verus serialize. It can't store internal references inside of an array and it can't store a nested object or an array containing objects before PHP 5.1.0.
However, I could deal with both of those so I created a benchmark. I used a single array containing from 10 to 150 indexes. I've generate the elements' values randomly using booleans, nulls, integers, floats, and some nested arrays (the nested arrays are smaller averaging 5 elements but created similarly). The largest percentage of elements are short strings around 10-15 characters. While there is a small number of long strings (around 500 characters).
Benchmarking returned these results for 1000 * [total time] / [iterations (4000 in this case)]
serialize 3.656, 3.575, 3.68, 3.933, mean of 3.71
include 7.099, 5.42, 5.185, 6.076, mean of 5.95
eval 5.514, 5.204, 5.011, 5.788, mean of 5.38
Meaning serialize is around 1 and a half times faster than var_export for a single large array. include and eval were consistently very close but eval was usually a few tenths faster (eval did better this particular set of trials than usual). An opcode cache like APC might make include faster, but otherwise serialize is the best choice.
[#18] Glen [2007-05-23 17:47:32]
Like previously reported, i find var_export() frustrating when dealing with recursive structures. Doing a :
<?php
var_export($GLOBALS);
?>
fails. Interestingly, var_dump() has some logic to avoid recursive references. So :
<?php
var_dump($GLOBALS);
?>
works (while being more ugly). Unlike var_export(), var_dump() has no option to return the string, so output buffering logic is required if you want to direct the output.
[#19] Zorro [2005-09-04 23:24:08]
This function can't export EVERYTHING. Moreover, you can have an error on an simple recursive array:
$test = array();
$test["oops"] = & $test;
echo var_export($test);
=>
Fatal error: Nesting level too deep - recursive dependency? in ??.php on line 59
[#20] linus at flowingcreativity dot net [2005-07-04 09:50:05]
<roman at DIESPAM dot feather dot org dot ru>, your function has inefficiencies and problems. I probably speak for everyone when I ask you to test code before you add to the manual.
Since the issue of whitespace only comes up when exporting arrays, you can use the original var_export() for all other variable types. This function does the job, and, from the outside, works the same as var_export().
<?php
function var_export_min($var, $return = false) {
if (is_array($var)) {
$toImplode = array();
foreach ($var as $key => $value) {
$toImplode[] = var_export($key, true).'=>'.var_export_min($value, true);
}
$code = 'array('.implode(',', $toImplode).')';
if ($return) return $code;
else echo $code;
} else {
return var_export($var, $return);
}
}
?>
[#21] paul at worldwithoutwalls dot co dot uk [2004-11-24 11:22:46]
var_export() differs from print_r() for variables that are resources, with print_r() being more useful if you are using the function for debugging purposes.
e.g.
<?php
$res = mysql_connect($dbhost, $dbuser, $dbpass);
print_r($res); //output: Resource id #14
var_export($res); //output: NULL
?>
[#22] php_manual_note at bigredspark dot com [2003-10-16 00:43:11]
[john holmes]
True, but that method would require you to open and read the file into a variable and then unserialize it into another variable.
Using a file created with var_export() could simply be include()'d, which will be less code and faster.
[kaja]
If you are trying to find a way to temporarily save variables into some other file, check out serialize() and unserialize() instead - this one is more useful for its readable property, very handy while debugging.
[original post]
If you're like me, you're wondering why a function that outputs "correct PHP syntax" is useful. This function can be useful in implementing a cache system. You can var_export() the array into a variable and write it into a file. Writing a string such as
<?php
';
$string = '<?php $array = ' . $data . '; ?>
?>
where $data is the output of var_export() can create a file that can be easily include()d back into the script to recreate $array.
The raw output of var_export() could also be eval()d to recreate the array.
---John Holmes...