php中var_dump()函数的详解说明

发布:smiling　来源: PHP粉丝网　添加日期：2014-09-13 21:15:24　浏览: 评论：0　

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,代码如下:

<?php

$a = "alsdflasdf;a";

$b = var_dump($a);

echo "<br>";

//var_dump($c);

$d=var_dump($c);

echo "<br>";

echo $a;

echo "<br>";

echo $b;

echo "<br>";

//输出：

string(12) "alsdflasdf;a"

NULL

alsdflasdf;a

例2,var_dump() 示例,代码如下:

<?php

$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<?php ?>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,对于第一种说,就多了一步操作,下来我们用数据说话吧,代码如下:

<?php

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:

//开源代码phpfensi.com

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)