preg_match :print: class matches tab character

Question

for($i = 0; $i < 255; $i++)
    if (preg_match('@[[:print:]]@', chr($i))) echo "chr($i) matches :print:<br>"; else echo "chr($i) doesnt match :print:<br>";

On my Windows system, the output for chr(9) is:

chr(9) matches :print:

With the same code, on a Linux system, the output is:

chr(9) doesnt match :print:

Why does the :print: class match \t on Windows only?

• PHP 5.5.12

Answer 1

It could be a locale issue, but then you must have a very funky locale on your hands. POSIX says that no cntrl can be print, and no space or blank can be print unless it's the space character itself. In the "C" locale, tab is all of cntrl, space, and blank; it seems like a very strange locale that would consider it none of those.