求问，json_encode结果为空值，变量为SDK封装xml得到的php Array

Array ( [0] => OSS\Model\ObjectInfo Object ( [key:OSS\Model\ObjectInfo:private] => user-dir/000001/ [lastModified:OSS\Model\ObjectInfo:private] => 2016-07-03T13:38:53.000Z [eTag:OSS\Model\ObjectInfo:private] => "D41D8CD98F00B204E9800998ECF8427E" [type:OSS\Model\ObjectInfo:private] => Normal [size:OSS\Model\ObjectInfo:private] => 0 [storageClass:OSS\Model\ObjectInfo:private] => Standard ) [1] => OSS\Model\ObjectInfo Object ( [key:OSS\Model\ObjectInfo:private] => user-dir/000001/whitefox.mp4 [lastModified:OSS\Model\ObjectInfo:private] => 2016-07-03T13:39:33.000Z [eTag:OSS\Model\ObjectInfo:private] => "0155231CC1EB8E35F15BE405F148570C" [type:OSS\Model\ObjectInfo:private] => Normal [size:OSS\Model\ObjectInfo:private] => 7888133 [storageClass:OSS\Model\ObjectInfo:private] => Standard ) [2] => OSS\Model\ObjectInfo Object ( [key:OSS\Model\ObjectInfo:private] => user-dir/000001/z.txt [lastModified:OSS\Model\ObjectInfo:private] => 2016-07-03T13:39:11.000Z [eTag:OSS\Model\ObjectInfo:private] => "29E31B02C673E32E36C790D40F8014D0" [type:OSS\Model\ObjectInfo:private] => Normal [size:OSS\Model\ObjectInfo:private] => 2012 [storageClass:OSS\Model\ObjectInfo:private] => Standard ) )

array (size=3) 0 => object(OSS\Model\ObjectInfo)[8] private 'key' => string 'user-dir/000001/' (length=16) private 'lastModified' => string '2016-07-03T13:38:53.000Z' (length=24) private 'eTag' => string '"D41D8CD98F00B204E9800998ECF8427E"' (length=34) private 'type' => string 'Normal' (length=6) private 'size' => int 0 private 'storageClass' => string 'Standard' (length=8) 1 => object(OSS\Model\ObjectInfo)[7] private 'key' => string 'user-dir/000001/whitefox.mp4' (length=28) private 'lastModified' => string '2016-07-03T13:39:33.000Z' (length=24) private 'eTag' => string '"0155231CC1EB8E35F15BE405F148570C"' (length=34) private 'type' => string 'Normal' (length=6) private 'size' => int 7888133 private 'storageClass' => string 'Standard' (length=8) 2 => object(OSS\Model\ObjectInfo)[9] private 'key' => string 'user-dir/000001/z.txt' (length=21) private 'lastModified' => string '2016-07-03T13:39:11.000Z' (length=24) private 'eTag' => string '"29E31B02C673E32E36C790D40F8014D0"' (length=34) private 'type' => string 'Normal' (length=6) private 'size' => int 2012 private 'storageClass' => string 'Standard' (length=8)

୧(˶‾᷄ ⁻̫ ‾᷅˵)୩，手册说了这个方法，除了资源型，其他都可以处理，但是传参必须是utf-8

var_dump是这样的，