如何防止php fwrite（）覆盖文件上的一行文本？

Question

I have extracted following lines of code from my script.

    $i=0;
    $j=0;
    $fp=fopen('C:\xampp\htdocs\Lib_auto_project\Deleted_Records\delete_log.sql','a+');// File where the string is to be written
    foreach($_POST as $temp)//repeat for all the values passed from the form
    {
        if($j==0)
          {     
               $result_set=$mysqli->query("select * from {$_SESSION['table_name_1']} where Copyid=$temp");
               $result_set=$result_set->fetch_array(MYSQL_BOTH);    
               ++$j;

           }
        if($temp!='Drop')// Drop is simply the value of submit buttom
         {
            $date=mysql_query("select now() as current_date_time") or die(mysql_error());
            $date=mysql_fetch_array($date,MYSQL_BOTH);
            $result="\n"."INSERT INTO delete_book_log  // this is the string begining with line break and followed by sql insert statement
                          VALUES(
                                 '{$result_set["Bid"]}',
                                 '$temp',
                                 '{$result_set["Name"]}',
                                 '{$result_set["Publication"]}',
                                 '{$result_set["ISBN"]}',
                                 '{$result_set["Author"]}',
                                 '{$result_set["Edition"]}',
                                 'in',
                                 '{$result_set["Book_Baseid"]}',
                                 '{$date['current_date_time']}'
                                 );";
              fflush($fp);
              fwrite($fp,$result);
              $mysqli->query("Delete from {$_SESSION['table_name_1']} where copyid=$temp");
              $i++;
          }

      }
      fclose($fp);

![screen shot]: http://i.stack.imgur.com/dOzSj.jpg

As you can see from the screen-shot, when one or more of the records are selected and the drop button is clicked, I want the records to be deleted from the database but want the corresponding sql insert statements to be written into a file(C:\\xampp\\htdocs\\Lib_auto_project\\Deleted_Records\\delete_log.sql) .For that to happen I have written the above piece of code. Now the problem is when I select the records and drop them all goes as desired. When I do the same any other instant I want similar sql insert strings, stored as shown above in $result, appended to the end of the file(C:\\xampp\\htdocs\\Lib_auto_project\\Deleted_Records\\delete_log.sql) . This does not quite happen. Rather the previously written strings get overwritten by the new one. I have tried it over and over but only the recent strings get overwrite the old ones.

Answer 1

It's nice that php says in the manual that a+ (using a should be just enough for you):

Open for reading and writing; place the file pointer at the end of the file. If the file does not exist, attempt to create it.

but try to run this code (called test.php ):

<?php    
$fp = fopen( 'test.php', 'a+') or die( 'Cannot open!');
echo 'Pos: ' . ftell($fp) ."\n";
echo fgets($fp);
echo 'Pos: ' . ftell($fp) ."\n";
fclose( $fp);

it'll generate this output:

Pos: 0
<?php
Pos: 6

You may either use fseek() :

fseek( $fp, 0, SEEK_END);

Or use file_put_contents() with proper parameters:

file_put_contents( $file, $string, FILE_APPEND);

And don't forget to check your file permissions and whether file was opened successfully by code like this:

if( !$fp){ 
    die( 'File cannot be opened!');
}

Answer 2

Try to use file_get_contents and file_put_contents instead of fwrite, and append your queries to array or string:

$fp=file_get_contents('C:\xampp\htdocs\Lib_auto_project\Deleted_Records\delete_log.sql');// File where the string is to be written
foreach($_POST as $temp)//repeat for all the values passed from the form
{
    if($j==0)
      {     
           $result_set=$mysqli->query("select * from {$_SESSION['table_name_1']} where Copyid=$temp");
           $result_set=$result_set->fetch_array(MYSQL_BOTH);    
           ++$j;

       }
    if($temp!='Drop')// Drop is simply the value of submit buttom
     {
        $date=mysql_query("select now() as current_date_time") or die(mysql_error());
        $date=mysql_fetch_array($date,MYSQL_BOTH);
        $result="\n"."INSERT INTO delete_book_log  // this is the string begining with line break and followed by sql insert statement
                      VALUES(
                             '{$result_set["Bid"]}',
                             '$temp',
                             '{$result_set["Name"]}',
                             '{$result_set["Publication"]}',
                             '{$result_set["ISBN"]}',
                             '{$result_set["Author"]}',
                             '{$result_set["Edition"]}',
                             'in',
                             '{$result_set["Book_Baseid"]}',
                             '{$date['current_date_time']}'
                             );";
          $fp .= $result . "\r\n";
          $mysqli->query("Delete from {$_SESSION['table_name_1']} where copyid=$temp");
          $i++;
      }

  }
  file_put_contents($fp);