php中var_dump()函數的詳解說明_PHP教程

本文章給大家全面的介紹一下關於php中var_dump()函數用法詳解，大家可參考參考。

var_dump()

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

var_dump()方法是判斷一個變數的類型與長度,並輸出變數的數值,如果變數有值輸的是變數的值並回返資料類型.
此函數顯示關於一個或多個運算式的結構資訊，包括運算式的類型與值。數組將遞迴展開值，通過縮排顯示其結構。

例1

代碼如下	複製代碼
$a = "alsdflasdf;a"; $b = var_dump($a); echo " "; //var_dump($c); $d=var_dump($c); echo " "; echo $a; echo " "; echo $b; echo " "; 輸出： string(12) "alsdflasdf;a" NULL alsdflasdf;a

例2

1. var_dump() 樣本

代碼如下	複製代碼
$a = array (1, 2, array ("a", "b", "c"));var_dump ($a); /* 輸出： 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); /* 輸出： float(3.1) bool(true) */ ?>

var_export和serialize做數組緩衝

$str = serialize($arr); 這兩種機制轉換之後的字串是不一樣的，第一種是數組的原型模式，第二種是序列化後的形式。第一 種存入檔案中的只要加上標籤，就形式了一個可用的數組原型，對調用來說，不用轉換，直接返回這個數組就可以，但第二種，則需要再用一次unserialize函數反序 列化一下。對於第種一說，就多了一步操作。下來我們用資料說話吧:

代碼如下

複製代碼

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)

由上面資料說明： var_export函數效能比serialize函數效能差一倍，而 unserialize時間也需要和serialize差不多的時間，serialize加上unserialize時間，和用var_export時間 差不多。

http://www.bkjia.com/PHPjc/445634.htmlwww.bkjia.comtruehttp://www.bkjia.com/PHPjc/445634.htmlTechArticle本文章給大家全面的介紹一下關於php中var_dump()函數用法詳解，大家可參考參考。 var_dump() void var_dump ( mixed expression [, mixed expression [, ...]] )...

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