PHP写文件到指定位置

 <?php
     $fp = fopen("output.json", "r+");
     $flag = fseek($fp, -3, SEEK_END);
     if(!$flag){
         echo "Offset success\r\n";
     }
     else{
         echo "Offset failed\n";
     }
     $flag = fwrite($fp, ",\n{HelloWorld}\n]");
     if($flag){
         echo "Have written";
     }
     else{
         echo "Write Failed";
     }
  ?>

data=[
{latitude: 42.363400, longitude: -71.098465, info: 'Speed = 21'},
]

在Json字符串中添加项