php - 数组变量未打印出 while 循环

Question

我在 while 循环之外初始化一个数组变量，问题是当这个数组变量从 while 循环中打印出来时，数组不显示，而当这个数组变量在循环中打印时，数组显示。

<?php 
  $all_rollno="";
  //Get Current Session
  $Res_Sess = mysql_query("SELECT sessionid from tbl_session where status=1 ORDER BY sessionid desc limit 1");
  $Row_Sess = mysql_fetch_array($Res_Sess);
  $Session = $Row_Sess[0];

 //Get Batch
 $Res_Bat = mysql_query("SELECT batchid,batchname,code FROM tbl_batch where status=1 and batchid!=12 ORDER BY batchid asc");

 while($Row_Bat = mysql_fetch_array($Res_Bat)){
     $Batch = $Row_Bat['batchid'];
     $Bat_Code = $Row_Bat['code'];

     //Present - Attendance
     $Patt4 = mysql_query("select count(id),rollno from tbl_attendance where batchid = '$Batch' and sessionid = '$Session' and attend = 1 GROUP by rollno");

     $arraytpresent="";
     $array_rollno="";
     $ipresent=0;
     while($Row_P4 = mysql_fetch_array($Patt4)){
        $arraytpresent[$ipresent] = round(($Row_P4[0]/$maxValue*100),0);
        $array_rollno[$ipresent] = $Row_P4[1];
        $ipresent++;
     }
     if(sizeof($all_rollno)>0){
         $all_rollno = array_merge($all_rollno,$array_rollno);
     } else {
         $all_rollno = $array_rollno;
    }
    //print_r($all_rollno);
}
print_r($all_rollno);

Answer 1

在下面的代码中，我做了 4 处更改:

<?php
  $all_rollno=array(); // 1. changed it to array

  // get the session
  $Res_Sess = mysql_query("SELECT sessionid from tbl_session where status=1 ORDER BY sessionid desc limit 1");
  $Row_Sess = mysql_fetch_array($Res_Sess);
  $Session = $Row_Sess[0];

  // get the list of badges
 $Res_Bat = mysql_query("SELECT batchid,batchname,code FROM tbl_batch where status=1 and batchid!=12 ORDER BY batchid asc");

 // loop and get the total attendance
 while($Row_Bat = mysql_fetch_array($Res_Bat)){
     $Batch = $Row_Bat['batchid'];
     $Bat_Code = $Row_Bat['code'];

     $Patt4 = mysql_query("select count(id),rollno from tbl_attendance where batchid = '$Batch' and sessionid = '$Session' and attend = 1 GROUP by rollno");

     $arraytpresent=array(); // 2. changed it to array
     $array_rollno=array(); // 3. changed it to array
     $ipresent=0;
     while($Row_P4 = mysql_fetch_array($Patt4)){
        $arraytpresent[$ipresent] = round(($Row_P4[0]/$maxValue*100),0);
        $array_rollno[$ipresent] = $Row_P4[1];
        $ipresent++;
     }

     // merge the data
     $all_rollno = array_merge($all_rollno,$array_rollno); // 4.Merge with the array no need for the if condition.
}
print_r($all_rollno);

请注意，mysql 已被弃用，因此请改用 mysqli/PDO。