PHP - Open TXT file, add +1 to contents when link clicked

Question

How can I make it so when a user clicks on a link on my web page, it writes to a .txt file named "Count.txt", which contains only a number and adds 1 to that number? Thank you.

Answer 1

If you forego any validity checking you could do it with something as simple as:

file_put_contents($theCounterFile, file_get_contents($theCounterFile)+1);

Addition:

There's talk about concurrency in this thread and it should be noted that it is a good idea to use a database and transactions to deal with concurrency, I'd highly recommend against writing a bunch of plumbing code to do this in a file.

If you've ever had, or think you might ever have two requests for the resource in the same second you should look into PDO with mysql, or PDO with SQLite instead of a file, use transactions (and InnoDB or better if you're going for mysql).

But really, even if you get two requests in the same microsecond (highly unlikely), chances of locking the file are slim as it will not be kept open and the two requests will probably not be handled parallel enough to lock anyway. Reality check: how many hits on the same resource do you get on average in the same minute?...

Answer 2

Generally this is quite easy:

$count = (int)file_get_contents('/path/to/Count.txt');
file_put_contents('/path/to/Count.txt', $count++, LOCK_EX);

But you'll run into concurrency problems using this code. One way to generate a lock safe from any race condition is:

$countFile = '/path/to/Count.txt';
$countTemp = tempnam(dirname($countFile), basename($countFile));
$countLock = $countFile . '.lock';
$f_lock = fopen($countLock, 'w'); 
if(flock($f_lock, LOCK_EX)) {
    $currentCount = (int)file_get_contents($countFile);
    $f_temp = fopen($countTemp, 'w');
    if(flock($f_temp, LOCK_EX)) {
        fwrite($f_temp, $currentCount++); 
        flock($f_temp, LOCK_UN); 
        fclose($f_temp); 
        if(!rename($countTemp, $countFile)) { 
            unlink($countTemp); 
        } 
    }
    flock($f_lock, LOCK_UN);
    fclose($f_lock); 
}

Answer 3

If you decide to do anything more advanced, like say two numbers, you may want to consider using SQLite. It's about as about as fast and as simple as opening and closing a file, but is much more flexible.

Answer 4

Open the file, lock the file (VERY important), read the number currently in there, add 1 to the number, write number back to file, release the lock and close the file.

ie. something like :

$fp = fopen("count.txt", "r+");

if (flock($fp, LOCK_EX)) { // do an exclusive lock
    $num = fread($fp, 10);
    $num++;
    fseek($fp, 0);
    fwrite($fp, $num);
    flock($fp, LOCK_UN); // release the lock
} else {
    // handle error
}
fclose($fp);

should work (not tested).