# PHP的feof()方法需要注意的地方

if(file_exists($pmr_config["datasetfile"])){$tmp_counter = 0;
$hd = fopen($pmr_config["datasetfile"], "r");
if($hd !== FALSE){ while (!feof($hd)) {
$buffer = fgets($hd);
if($tmp_counter >=$seq){
$result[] =$buffer;
}
$tmp_counter++; if($tmp_counter >=$seq +$size){
break;
}
}
}else{
echo "warning:open file {$pmr_config["datasetfile"]} failed!PHP_EOL"; } }else{ echo "warning:file {$pmr_config["datasetfile"]} does not exsits!PHP_EOL";
}




<?php
// if file can not be read or doesn't exist fopen function returns FALSE
$file = @fopen("no_such_file", "r"); // FALSE from fopen will issue warning and result in infinite loop here while (!feof($file)) {
}

fclose($file); ?>  feof() is, in fact, reliable. However, you have to use it carefully in conjunction with fgets(). A common (but incorrect) approach is to try something like this: <?$fp = fopen("myfile.txt", "r");
while (!feof($fp)) {$current_line = fgets($fp); // do stuff to the current line here } fclose($fp);
?>


The problem when processing plain text files is that feof() will not return true after getting the last line of input.  You need to try to get input _and fail_ before feof() returns true.  You can think of the loop above working like this:

* (merrily looping, getting lines and processing them)
* fgets used to get 2nd to last line
* line is processed
* loop back up -- feof returns false, so do the steps inside the loop
* fgets used to get last line
* line is processed
* loop back up -- since the last call to fgets worked (you got the last line), feof still returns false, so you do the steps inside the loop again
* fgets used to try to get another line (but there's nothing there!)
* your code doesn't realize this, and tries to process this non-existent line (typically by doing the same actions again)
* now when your code loops back up, feof returns true, and your loop ends

There's two ways to solve this:

1. You can put an additional test for feof() inside the loop
2. You can move around your calls to fgets() so that the testing of feof() happens in a better location

Here's solution 1:

<?
$fp = fopen("myfile.txt", "r"); while(!feof($fp)) {
$current_line = fgets($fp);
if (!feof($fp)) { // process current line } } fclose($fp);
?>


And here's solution 2 (IMHO, more elegant):

<?
$fp = fopen("myfile.txt", "r");$current_line = fgets($fp); while (!feof($fp)) {
// process current line
$current_line = fgets($fp);
}
fclose(\$fp);
?>


FYI, the eof() function in C++ works the exact same way, so this isn't just some weird PHP thing...

Codefor
posted @ 2011-07-07 16:18  Codefor  阅读(3950)  评论(0编辑  收藏  举报