php中json_decode及foreach使用总结

<?php
$arr=array();
//例子1
$json_str= '{"ret":"OK","questions":{
    "1":{"qid":"1","title":"\u95ee\u98981111",
    "answers":{
    "1":{"cid":"1","title":"A","cont":"\u7b54\u68481-1","iscorrect":"1","qid":"1"},
    "2":{"cid":"2","title":"B","cont":"\u7b54\u68481-2","iscorrect":"0","qid":"1"},
    "3":{"cid":"3","title":"C","cont":"\u7b54\u68481-3","iscorrect":"0","qid":"1"}
    }},
    "2":{"qid":"2","title":"\u95ee\u98982222", 
    "answers":{"5":{
    "cid":"5","title":"A","cont":"\u7b54\u68482-1","iscorrect":"0","qid":"2"},
    "6":{"cid":"6","title":"B","cont":"\u7b54\u68482-2","iscorrect":"0","qid":"2"},
    "7":{"cid":"7","title":"A","cont":"aa","iscorrect":"0","qid":"2"},
    "8":{"cid":"8","title":"D","cont":"\u7b54\u68482-4","iscorrect":"0","qid":"2"}}}}}';
// 相关错误反馈
// Notice: Undefined offset: 1
// Notice: Trying to get property of non-object
// Notice: Undefined offset: 0
// Notice: Array to string conversion

//json_decode不加参数true，转成的就不是array,而是对象 [questions] => stdClass Object
$arr=json_decode($json_str,true);
// echo "<pre>";print_r($arr);exit;

//json_decode不加参数true，下面取值出错： Fatal error: Cannot use object of type stdClass as array in
//通过key:ret取值
 echo $arr["ret"];echo "<br/>";
 $arr_q=$arr["questions"];
//通过key取值
 echo " 1-title:";echo $arr["questions"]["1"]["answers"]["1"]["title"];
 echo " 8-title:";echo $arr["questions"]["2"]["answers"]["8"]["title"];
 $arr_q1a=$arr["questions"]["1"]["answers"];
 $arr_q2a=$arr["questions"]["2"]["answers"];
 echo "<br>";echo" q1a:"; var_dump($arr_q1a);
 
 $m=count($arr_q1a);echo "m:$m ";
 $n=count($arr_q2a);echo "n:$n ";

//这个打印就有值 t1:1 t1:2 t1:3
 for($i=1;$i<=$m;$i++){
     echo " t1:";echo $arr_q1a[$i]['cid'];
 }
 //这种for会漏值 T2: T2: T2: T2:  按说应该是 5 6 7 8 
 for($i=1;$i<=$n;$i++){
     echo " T2:";echo $arr_q2a[$i]['cid'];
 }
 //for循环key和value转换就很不方便
 foreach ($arr_q2a as $key => $value){
     echo "questions 2 : ".$key."->".$value." ";
 }
//多维数组，最好用foreach方便 
foreach ($arr_q as $key1=>$value1){
    echo "<br>"; echo $key1;
    foreach ($value1['answers'] as $key2=>$value2){
        echo "<br>"; echo $key2."->".$value2; 
        foreach ($value2 as $key3=>$value3){
            echo $key3."->".$value3." ";
        }
    }
}

//例子2
$json= '[{"id":"1","name":"\u5f20\u96ea\u6885","age":"27","subject":"\u8ba1\u7b97\u673a\u79d1\u5b66\u4e0e\u6280\u672f"},{"id":"2","name":"\u5f20\u6c9b\u9716","age":"21","subject":"\u8f6f\u4ef6\u5de5\u7a0b"}]';

// $students= json_decode($json,true);//得到的是 array
//echo "<pre>";print_r($students);
// for($i=0;$i<count($students);$i++){
//     echo "姓名：".$students[$i]['name']."&nbsp;&nbsp;&nbsp;年 龄：".$students[$i]['age']."&nbsp;&nbsp;&nbsp;专 业：".$students[$i]['subject']."<br />";
// }
$students= json_decode($json);//得到的是 object
foreach($students as $obj){
    echo "姓名：".$obj->name."年龄：".$obj->age."专业：".$obj->subject."<br/>";
}
?>

总结，php中的多维数组，最好用foreach。