PHP中echo、print_r()和var_dump()怎么用

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echo：输出一个或多个字符串。

print_r()：打印关于变量的易于理解的信息（仅返回结果）。

var_dump()：显示关于一个或多个表达式的结构信息（返回表达式的类型与值）。

$arr=array(    array('a'=>'1','b'=>'2','c'=>'3'),    array('a'=>'11','b'=>'22','c'=>'33'),    array('a'=>'111','b'=>'222','c'=>'333'));$json=json_encode($arr);echo $json;#输出结果/**[{"a":"1","b":"2","c":"3"},{"a":"11","b":"22","c":"33"},{"a":"111","b":"222","c":"333"}]**/print_r($json);#打印结果/**[{"a":"1","b":"2","c":"3"},{"a":"11","b":"22","c":"33"},{"a":"111","b":"222","c":"333"}]**/var_dump($json);#返回结果/**string(88) "[{"a":"1","b":"2","c":"3"},{"a":"11","b":"22","c":"33"},{"a":"111","b":"222","c":"333"}]"**/print_r($arr);#打印结果/**Array(    [0] => Array        (            [a] => 1            [b] => 2            [c] => 3        )    [1] => Array        (            [a] => 11            [b] => 22            [c] => 33        )    [2] => Array        (            [a] => 111            [b] => 222            [c] => 333        ))**/var_dump($arr);#返回结果/**array(3){    [0] => array(3)    {        ["a"] => string(1) "1"        ["b"] => string(1) "2"        ["c"] => string(1) "3"    }    [1] => array(3)    {        ["a"] => string(2) "11"        ["b"] => string(2) "22"        ["c"] => string(2) "33"    }    [2] => array(3)    {        ["a"] => string(3) "111"        ["b"] => string(3) "222"        ["c"] => string(3) "333"    }}**/

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