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PHP中print_r、var_export、var_dump用法介绍

Jun 13, 2016 am 10:03 AM
dump export php print var introduce about article usage

文章详细的介绍了关于PHP中print_r、var_export、var_dump区别比较以及这几个在php不同的应用中的用法,有需要的朋友可以参考一下

可以看出print_r跟var_export都是可以作为返回值的,只需要把第二个参数设置为true即可

print_r
(PHP 4 , PHP 5)print_r –  打印关于变量的易于理解的信息。

描述
bool print_r ( mixed expression [, bool return])

注: 参数 return 是在 PHP 4.3.0 的时候加上的

print_r() 显示关于一个变量的易于理解的信息。如果给出的是 string、integer 或 float,将打印变量值本身。如果给出的是 array,将会按照一定格式显示键和元素。object 与数组类似。

记住,print_r() 将把数组的指针移到最后边。使用 reset() 可让指针回到开始处。

 

 代码如下 复制代码

<br>
<?php <br />
$a = array ('a' => 'apple', 'b' => 'banana', 'c' => array ('x','y','z'));<br>
print_r ($a);<br>
?><br>
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上边的代码将输出:

 代码如下 复制代码

<br>
Array<br>
(<br>
    [a] => apple<br>
    [b] => banana<br>
    [c] => Array<br>
        (<br>
            [0] => x<br>
            [1] => y<br>
            [2] => z<br>
        )<br>
)<br>
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如果想捕捉 print_r() 的输出,可使用 return 参数。若此参数设为 TRUE,print_r() 将不打印结果(此为默认动作),而是返回其输出。

 

例子 1. return 参数示例

 代码如下 复制代码

$b = array ('m' => 'monkey', 'foo' => 'bar', 'x' => array ('x', 'y', 'z'));
$results = print_r ($b, true); //$results 包含了 print_r 的输出结果
?> 
 

 

注: 如果想在 PHP 4.3.0 之前的版本中捕捉 print_r() 的输出,可使用输出控制函数。

注: 在 PHP 4.0.4 之前的版本中,如果给出的 array 或 object 包含了直接或间接指向自身的引用,print_r() 将永远继续下去。print_r($GLOBALS) 就是一个例子,因为 $GLOBALS 自身即是全局变量,其包含了指向自身的引用。

 

var_export
(PHP 4 >= 4.2.0, PHP 5)var_export – 输出或返回一个变量的字符串表示

描述
mixed var_export ( mixed expression [, bool return])

此函数返回关于传递给该函数的变量的结构信息,它和 var_dump() 类似,不同的是其返回的表示是合法的 PHP 代码。

您可以通过将函数的第二个参数设置为 TRUE,从而返回变量的表示。

比较 var_export() 和 var_dump().

 

 代码如下 复制代码

<br>
<?php <br />
$a = array (1, 2, array ("a", "b", "c"));<br>
var_export ($a); /* 输出:<br>
array (<br>
0 => 1,<br>
1 => 2,<br>
2 =><br>
array (<br>
0 => 'a',<br>
1 => 'b',<br>
2 => 'c',<br>
),<br>
)<br>
*/
<p>$b = 3.1;<br>
$v = var_export($b, TRUE);<br>
echo $v;</p>
<p>/* 输出:<br>
3.1<br>
*/<br>
?><br>
</p>
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  var_dump
(PHP 3>= 3.0.5, PHP 4 , PHP 5)var_dump – 打印变量的相关信息

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

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。

提示: 为了防止程序直接将结果输出到浏览器,您可以使用输出控制函数(output-control functions)来捕获函数的输出,并把它们保存到一个 string 型的变量中。

可以比较一下 var_dump() 与 print_r()。

 

例子 1. var_dump() 示例

 代码如下 复制代码

<br>
<?php <br />
$a = array (1, 2, array ("a", "b", "c"));<br>
var_dump ($a); /* 输出:<br>
array(3) {<br>
[0]=><br>
int(1)<br>
[1]=><br>
int(2)<br>
[2]=><br>
array(3) {<br>
[0]=><br>
string(1) "a"<br>
[1]=><br>
string(1) "b"<br>
[2]=><br>
string(1) "c"<br>
}<br>
}*/
<p> </p>
<p>$b = 3.1;<br>
$c = TRUE;<br>
var_dump($b,$c);</p>
<p>/* 输出:<br>
float(3.1)<br>
bool(true)*/</p>
<p>?><br>
</p>
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