php中var_dump()函数的详解说明-php教程

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)

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.

php中var_dump()函数的详解说明

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