void var_dump ( mixed expression [, mixed expression [, ...]] )

var_dump()方法是判断一个变量的类型与长度,并输出变量的数值,如果变量有值输的是变量的值并回返数据类型.
此函数显示关于一个或多个表达式的结构信息，包括表达式的类型与值。数组将递归展开值，通过缩进显示其结构。
例1：

$a = "alsdflasdf;a";  
$b = var_dump($a);  
var_dump($b);   
echo $a;   
输出：  
string(12) "alsdflasdf;a" 
NULL  
alsdflasdf;a 

例2：1. var_dump() 示例

    $a = array (1, 2, array ("a", "b", "c"));  
var_dump ($a);  
   
/* 输出： array(3) {   [0]=>   int(1)   [1]=>   int(2)   [2]=>   array(3) {     [0]=>     string(1) "a"     [1]=>     string(1) "b"     [2]=>     string(1) "c"   } }
*/ 
$b = 3.1; $c = TRUE; var_dump($b,$c);  
/* 输出： float(3.1) bool(true)
*/ 

  var_export和serialize做数组缓存

$str = serialize($arr); 这两种机制转换之后的字符串是不一样的，第一种是数组的原型模式，第二种是序列化后的形式。第一 种存入文件中的只要加上标签，就形式了一个可用的数组原型，对调用来说，不用转换，直接返回这个数组就可以，但第二种，则需要再用一次unserialize函数反序 列化一下。对于第种一说，就多了一步操作。下来我们用数据说话吧:

set_time_limit(50); $a = array(1,2,3); $b = array('a'=>1, 'b'=>2, 'c'=>3); $c = array('a'=>array(1,2,3), 'b'=>array(4,5,6));  
$time1 = microtime(true);  
$times = 1000000; #10w  
for($i=1; $i<=$times; $i++){  $A = var_export($a, true); }  
$time2 = microtime(true);  
for($i=1; $i<=$times; $i++){  $B = var_export($b, true); }  
$time3 = microtime(true);  
for($i=1; $i<=$times; $i++){  $C = var_export($c, true); }  
$time4 = microtime(true);  
for($i=1; $i<=$times; $i++){  $X = serialize($a); }  
$time5 = microtime(true);  
for($i=1; $i<=$times; $i++){  $Y = serialize($b); }  
$time6 = microtime(true);  
for($i=1; $i<=$times; $i++){  $Z = serialize($c); }  
$time7 = microtime(true);  
for($i=1; $i<=$times; $i++){  $O = unserialize($X); }  
$time8 = microtime(true);  
for($i=1; $i<=$times; $i++){  $P = unserialize($Y); }  
$time9 = microtime(true);  
for($i=1; $i<=$times; $i++){  $Q = unserialize($Z); } $time10 = microtime(true);  
$var_export_time['a'] = $time2 - $time1; $var_export_time['b'] = $time3 - $time2; $var_export_time['c'] = $time4 - $time3;  
$serialize_time['a'] = $time5 - $time4; $serialize_time['b'] = $time6 - $time5; $serialize_time['c'] = $time7 - $time6;  
$unserialize_time['a'] = $time8 - $time7; $unserialize_time['b'] = $time9 - $time8; $unserialize_time['c'] = $time10 - $time9; print_r($var_export_time); print_r($serialize_time); print_r($unserialize_time); ?> output: Array(    [a] => 3.3401498794556    [b] => 5.1394801139832    [c] => 8.8483898639679)Array(    [a] => 1.6063709259033    [b] => 1.7033960819244    [c] => 3.4534389972687)Array(    [a] => 1.6037359237671    [b] => 1.817803144455    [c] => 3.7992968559265) 

由上面数据说明： var_export函数性能比serialize函数性能差一倍，而 unserialize时间也需要和serialize差不多的时间，serialize加上unserialize时间，和用var_export时间 差不多。