windows,linux all meet this bug

I don't really understand the issue you have from your example, but in general LF is the compile-default linebreak for PCRE. If you want to use a different linebreak character you can either compile PCRE with the appropriate option or specify a control option like (*CRLF) before your regular expression.

I don't understand the issue either. The code behaves the same way for me 
regardless of the line ending in test.txt.

Can you provide a simpler example, please?

Test script:
---------------
<?php
$file = fopen("test.txt","r");
while(!feof($file)){
	$line = fgets($file);
	preg_match('/^(.+) (.+)$/',$line,$matches);
	echo $line;	
	if(array_key_exists(1, $matches) && array_key_exists(2, $matches))
	echo $matches[1].$matches[2];
}
fclose($file);
?>
test.txt must be created in windows
abc def
ghi jklm
nop

Expected result:
----------
abc def
abcdef
ghi jklm
ghijklm
nop

Actual result:
----------
abc def
ghi jklm
nopjklm

$matches[2] follow character <CR>

Ok. here is my guess at what is confusing you.

By default PCRE uses \n to indicate the end of a line. Your files have \r\n at 
the end, so I think the only confusion you have is that your second match will 
have \r included in it and when you then print this on the console it looks 
essentially invisible.

In your latest example there, try changing your output line to this:

echo $matches[1].trim($matches[2]);

Does it make more sense now?

Yes,thanks.That is it