PHP的feof()方法需要注意的地方

简介：这是PHP的feof()方法需要注意的地方的详细页面，介绍了和php,有关的知识、技巧、经验，和一些php源码等。

class='pingjiaF' frameborder='0' src='http://biancheng.dnbcw.info/pingjia.php?id=340516' scrolling='no'>自己曾写过这样一段代码：

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";
}

其中当读取行数包括文件结尾的时候，$result数组中总会比期望的内容多出来一个元素：

(boolean)false

按说，如果读取到最后一行，feof函数会返回TRUE，然后while循环就退出了，为什么不是呢？

while (!feof($hd)) {

事情原来是这样子的：

<?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...

Ref: http://cn.php.net/manual/en/function.feof.php
爱J2EE关注Java迈克尔杰克逊视频站JSON在线工具
http://biancheng.dnbcw.info/php/340516.html pageNo:7