PHP输出JSON格式数据方式

<?php
    $libstatis='{
	"code": 0,
	"data": [{
		"answer_count": 14,
		"created_at": "2019-09-06 16:35:06",
		"id": 1,
		"level": 1,
		"name": "初级题库",
		"questions_count": 171
	}, {
		"answer_count": 9,
		"created_at": "2019-09-06 16:35:20",
		"id": 2,
		"level": 2,
		"name": "中级题库",
		"questions_count": 15
	}, {
		"answer_count": 0,
		"created_at": "2019-09-06 16:35:30",
		"id": 3,
		"level": 3,
		"name": "高级题库",
		"questions_count": 0
	}],
	"message": "操作成功"
    }';
 
    echo $libstatis;