Re: php seems to be inconsistent in its handling of backslashes ... maybe?

On Sun, April 22, 2007 12:54 am, ufan100@gmail.com wrote: > -- or maybe it's just the PCRE extension > -- or quite likely I have got something wrong > > Hello members, > I'm hoping you could enlighten me. > > Using error_reporting = E_ALL | E_STRICT, I tested the > following statements: PHP interprets \\ inside of '' to turn \\ into \ It also tries to be halfway smart about mistakes with \ followed by some other non-special character, by just pretending you knew what you were doing and had \\ there to get just one \, even though you didn't. PCRE *also* handles \ specially, to escape the next char, in most circumstances... > <?php > preg_match('#\\#','any-string'); => warning Original PHP sees PCRE sees #\\# #\# ## #\\\\# #\\# #\# #\\\\\# #\\\# #\#, I guess... Pretty much any "odd" number of \\ in a row is almost always wrong, unless one of them is \n, \t, \r, \$, or one of the hex or octal codes: http://us.php.net/manual/en/language.types.string.php > preg_match('#\\\#','any-string'); > preg_match('#\\\\#','any-string'); > preg_match('#\\\\\#','any-string'); => warning > preg_match('#\\\\\\#','any-string'); => warning > preg_match('#\\\\\\\#','any-string'); > ?> > > This seemed strange: > warnings with 2 and 6 backlashes For 2 backslashes, PHP "ate" the 2 backslashes, and handed PCRE #\#, and PCRE does not like that at all. > no warnings with 3, 7 > warning with 5 but not with 3 and 7. PHP and PCRE are doing their damndest to make sense of the garbage you typed, but if you type garbage, you get garbage. http://us.php.net/manual/en/language.types.string.php > The warning related of course to no matching delimeter '#' > being found. > > So I wrote a little test script (preg.php) to test up to 10 > backslashes: > > <?php > for($i=1; $i<=10; ++$i) { > echo "\n---------------------------------\n"; > echo "Number of '\\' is $i \n"; > $bs = '#'; > $bs .= str_repeat('\\',$i); Did you think this was giving you 1 or 2 \ chars? Cuz it only gives you ONE, since \ is also special inside of '' http://us.php.net/manual/en/language.types.string.php > This agrees with my understanding of backslash escaping (I > hope that's right) but now I can't understand why I got the > results earlier (shown in my first script). If you don't understand backslash, keep re-reading this: http://us.php.net/manual/en/language.types.string.php -- Some people have a "gift" link here. Know what I want? I want you to buy a CD from some indie artist. http://cdbaby.com/browse/from/lynch Yeah, I get a buck. So?