mysql foreach fwrite | 易学教程

问题

I use some code here, transfer mysql query data into json data and write into a file. where is the problem? why the file is zero kb?

while($row = mysql_fetch_array($Query)){ 
  $arr = array ('name'=>$row['name']);
  $jsondata = json_encode($arr);
  $countfile="data.txt";
  if(!file_exists($countfile))
  {
    fopen($countfile,"w");
  } 
  $fp = fopen($countfile, 'r');
  fwrite($fp, $jsondata);
  fclose($fp);
}

回答1:

Because you're reopening the file as read only

$fp = fopen($countfile, 'r');

try

$fp = fopen($countfile, 'w'); // to write

$fp = fopen($countfile, 'a'); // to append

you could also open the file for writing at the start, append your rows in a variable and then write it all together to the file.

$countfile="data.txt";
$fp = fopen($countfile, 'w');
while($row = mysql_fetch_array($Query))
{ 
    $arr = array ('name'=>$row['name']);
    $jsondata .= json_encode($arr) . "\n";

}
fwrite($fp, $jsondata);
fclose($fp);

回答2:

Several things.

You dont need (and should avoid) to open the file in every iteration
You open the file read-only (r)

At all something like this should do it

$countfile="data.txt";
$fp = fopen($countfile, 'w');
while($row = mysql_fetch_array($Query))
{ 
    $arr = array ('name'=>$row['name']);
    $jsondata = json_encode($arr);

    fwrite($fp, $jsondata);
}
fclose($fp);

Additional you append separate json structures into the file, what is probably not, what you want. You should first collect all you want to store into one json structure and save it then

$data = array();
while($row = mysql_fetch_array($Query))
{ 
    $data[] = array ('name'=>$row['name']);

}
file_put_contents('data.txt', json_encode($data));

This feels more like what you are probably looking for.

回答3:

You are opening the file read-only. You probably want 'w' or 'r+'.

回答4:

You are opening the file for reading only

$fp = fopen($countfile, 'r');

You also dont need

  if(!file_exists($countfile))
  {
    fopen($countfile,"w");
  }

just use:

$fp = fopen($countfile, 'w');

来源：https://stackoverflow.com/questions/6312535/mysql-foreach-fwrite

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php

foreach

fwrite