php中var_dump()函数的详解说明

时间：2015-01-23 来源：西部数据作者：西部数据

本文章给大家全面的介绍一下关于php中var_dump()函数用法详解，大家可参考参考。

var_dump()

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);

echo "

";

//var_dump($c);

$d=var_dump($c);

echo "

";

echo $a;

echo "

";

echo $b;

echo "

";

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)