How to move file pointer to previous line in php? - php

Question

Text file in question is named fp.txt and contains 01, 02, 03, 04, 05, ...10 on each line.
01
02
...
10
Code:
<?php
//test file for testing fseek etc
$file = "fp.txt";
$fp = fopen($file, "r+") or die("Couldn't open ".$file);
$count = 0;
while(!(feof($fp))){ // till the end of file
$text = fgets($fp, 1024);
$count++;
$dice = rand(1,2); // just to make/alter the if condition randomly
echo "Dice=".$dice." Count=".$count." Text=".$text."<br />";
if ($dice == 1){
fseek($fp, -1024, SEEK_CUR);
}
}
fclose($fp);
?>
So, because of fseek($fp, -1024, SEEK_CUR); is not working properly. What I want is that If Dice == 1, set the file-pointer to previous line i.e. one line up than the current one. But I think negative value is setting the file pointer to end of file, and thus ending the while loop before the actual end of file.
Desired Output is:
Dice=2 Count=1 Text=01
Dice=2 Count=2 Text=02
Dice=2 Count=3 Text=03
Dice=1 Count=4 Text=03
Dice=2 Count=5 Text=04
Dice=2 Count=6 Text=05
Dice=2 Count=7 Text=06
Dice=1 Count=8 Text=06
Dice=1 Count=9 Text=06
Dice=2 Count=10 Text=07
.... //and so on until Text is 10 (Last Line)
Dice=2 Count=n Text=10
Note that whenever dice is 2, text is same as previous one. Now it is just stopping at the first occurrence of Dice=1
So basically my question is How to move/relocate file-pointer to previous line?
Please note that dice=rand(1,2) is just for example. In the actual code, $text is a string and if condition is to be true when string does not contain a particular text.
EDIT:
Solved, both samples (#hakre 's & mine) are working as desired.

Answer 1

You read out a line from the file, but only forward to the next line when the dice is not 1.
Consider to use the SplFileObject for that, which offers an interface that is better for your scenario I'd say:
$file = new SplFileObject("fp.txt");
$count = 0;
$file->rewind();
while ($file->valid())
{
$count++;
$text = $file->current();
$dice = rand(1,2); // just to make alter the if condition randomly
echo "Dice=".$dice." Count=".$count." Text=".$text."<br />";
if ($dice != 1)
{
$file->next();
}
}

Answer 2

<?php
$file = "fp.txt";
$fp = fopen($file, "r+") or die("Couldn't open ".$file);
$eof = FALSE; //end of file status
$count = 0;
while(!(feof($fp))){ // till the end of file
$current = ftell($fp);
$text = fgets($fp, 1024);
$count++;
$dice = rand(1,2); // just to alter the if condition randomly
if ($dice == 2){
fseek($fp, $current, SEEK_SET);
}
echo "Dice=".$dice." Count=".$count." Text=".$text."<br />";
}
fclose($fp);
?>
This sample is also working as required.
The changes are:
* Addition of "$current = ftell($fp);" after while loop.
* Modification of fseek line in if condition.
* checking for dice==2 instead of dice==1