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:

1. <?php
2. $a = "alsdflasdf;a";
3. $b = var_dump($a);
4. echo "<br>";
5. //var_dump($c);
6. $d=var_dump($c);
7. echo "<br>";
8. echo $a;
9. echo "<br>";
10. echo $b;
11. echo "<br>";
12. //输出：
13. string(12) "alsdflasdf;a"
14. NULL
15. alsdflasdf;a

例2,var_dump() 示例,代码如下:

1. <?php
2. $a = array (1, 2, array ("a", "b", "c"));
3. var_dump ($a);
4. /* 输出：
5. array(3) {
6. [0]=>
7. int(1)
8. [1]=>
9. int(2)
10. [2]=>
11. array(3) {
12. [0]=>
13. string(1) "a"
14. [1]=>
15. string(1) "b"
16. [2]=>
17. string(1) "c"
18. }
19. }
20. */
21. $b = 3.1;
22. $c = TRUE;
23. var_dump($b,$c);
24. /* 输出：
25. float(3.1)
26. bool(true)
27. */
28. ?>

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:

1. <?php
2. set_time_limit(50);
3. $a = array(1,2,3);
4. $b = array('a'=>1, 'b'=>2, 'c'=>3);
5. $c = array('a'=>array(1,2,3), 'b'=>array(4,5,6));
6. $time1 = microtime(true);
7. $times = 1000000; #10w
8. for($i=1; $i<=$times; $i++){
9. $A = var_export($a, true);
10. }
11. $time2 = microtime(true);
12. for($i=1; $i<=$times; $i++){
13. $B = var_export($b, true);
14. }
15. $time3 = microtime(true);
16. for($i=1; $i<=$times; $i++){
17. $C = var_export($c, true);
18. }
19. $time4 = microtime(true);
20. for($i=1; $i<=$times; $i++){
21. $X = serialize($a);
22. }
23. $time5 = microtime(true);
24. for($i=1; $i<=$times; $i++){
25. $Y = serialize($b);
26. }
27. $time6 = microtime(true);
28. for($i=1; $i<=$times; $i++){
29. $Z = serialize($c);
30. }
31. $time7 = microtime(true);
32. for($i=1; $i<=$times; $i++){
33. $O = unserialize($X);
34. }
35. $time8 = microtime(true);
36. for($i=1; $i<=$times; $i++){
37. $P = unserialize($Y);
38. }
39. $time9 = microtime(true);
40. for($i=1; $i<=$times; $i++){
41. $Q = unserialize($Z);
42. }
43. $time10 = microtime(true);
44. $var_export_time['a'] = $time2 - $time1;
45. $var_export_time['b'] = $time3 - $time2;
46. $var_export_time['c'] = $time4 - $time3;
47. $serialize_time['a'] = $time5 - $time4;
48. $serialize_time['b'] = $time6 - $time5;
49. $serialize_time['c'] = $time7 - $time6;
50. $unserialize_time['a'] = $time8 - $time7;
51. $unserialize_time['b'] = $time9 - $time8;
52. $unserialize_time['c'] = $time10 - $time9;
53. print_r($var_export_time);
54. print_r($serialize_time);
55. print_r($unserialize_time);
56. ?>
57. //output:
58. //开源代码phpfensi.com
59. 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.