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

On Sun, April 22, 2007 12:54 am, ufan100@xxxxxxxxx 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?
.

Relevant Pages