From: ikindred at cox dot net Operating system: FreeBSD 4.9 PHP version: 4.3.4 PHP Bug Type: Documentation problem Bug description: strncmp using the length of the shorter string
Description: ------------ http://www.php.net/manual/en/function.strncmp.php says: "If any of the strings is shorter than len, then the length of that string will be used for the comparison." strncmp() does not behave in this manner. Not in PHP. Not in C. On reflection, I guess that PHP cannot just call the C library strncmp function, as C strings are terminated by \x00 while PHP strings are not so terminated and can therefore contain one or more \x00's. So, maybe, just maybe, this is not a documentation problem, but an actual PHP bug. There have been many times when I wished that len would fallback to the length of the shorter string... so perhaps this is not a documentation bug, but rather PHP bug???? For example, this usually happens when I am writing something like: // note the tedious to write, performance degrading call to strlen ("staticPrefix") if (strncmp ($dynamicString, "staticPrefix", strlen ("staticPrefix")) == 0) { print "dynamicString starts with staticPrefix\n"; } else { print "dynmaicString does not start with staticPrefix\n"; } If you decide this is a PHP bug (and not a documentation bug), then be careful, because "fixing" PHP will cause strncmp to behave significantly differently from its C language namesake and may break existing code. One solution might be to make $len optional. When $len is omitted, then the length of the shorter string is used. This should not break code and is also not flagrantly inconsistent with the C language strncmp. At present (PHP 4.3.4), omitting $len causes "Warning: Wrong parameter count for strncmp" and NULL is returned. But even this has a major problem - I was wrong - it will break code: if either string (even/especially the dynamic one) is null or "", then strncmp will say the strings are equal!!! This is not what I/we want. You can remedy this problem by only falling back to the length of the second string, or the first, as long as you are consistent. But I'd go with the second - that will look prettier if you have a whole bunch of strncmps one line after another with the same $dynamicString but different "staticPrefixes" of different lengths. Have fun deciding what to do! strncmp ($dynamic, "static") would definitely be useful, but it is assymetrical and un-C-like. But it would be useful. I'd say, go for it! The documentation will need to be changed anyways, so I'll leave this bug here as a documentation bug. If you agree that it's worth changing strncmp as I have described, once you fixed the docs, reclassify/forward this bug on. Thanks! Reproduce code: --------------- <?php print "a aa: ". strncmp ("a" , "aa", 100). "\n"; print "aa aa: ". strncmp ("aa", "aa", 100). "\n"; print "aa a : ". strncmp ("aa", "a" , 100). "\n"; ?> Expected result: ---------------- If strncmp behaved as described, I would expect the following (as len would "fallback" to 1 in the first and third cases): a aa: 0 aa aa: 0 aa a : 0 Actual result: -------------- The actual result: a aa: -1 aa aa: 0 aa a : 1 (This is what strncmp does in C.) -- Edit bug report at http://bugs.php.net/?id=26940&edit=1 -- Try a CVS snapshot (php4): http://bugs.php.net/fix.php?id=26940&r=trysnapshot4 Try a CVS snapshot (php5): http://bugs.php.net/fix.php?id=26940&r=trysnapshot5 Fixed in CVS: http://bugs.php.net/fix.php?id=26940&r=fixedcvs Fixed in release: http://bugs.php.net/fix.php?id=26940&r=alreadyfixed Need backtrace: http://bugs.php.net/fix.php?id=26940&r=needtrace Need Reproduce Script: http://bugs.php.net/fix.php?id=26940&r=needscript Try newer version: http://bugs.php.net/fix.php?id=26940&r=oldversion Not developer issue: http://bugs.php.net/fix.php?id=26940&r=support Expected behavior: http://bugs.php.net/fix.php?id=26940&r=notwrong Not enough info: http://bugs.php.net/fix.php?id=26940&r=notenoughinfo Submitted twice: http://bugs.php.net/fix.php?id=26940&r=submittedtwice register_globals: http://bugs.php.net/fix.php?id=26940&r=globals PHP 3 support discontinued: http://bugs.php.net/fix.php?id=26940&r=php3 Daylight Savings: http://bugs.php.net/fix.php?id=26940&r=dst IIS Stability: http://bugs.php.net/fix.php?id=26940&r=isapi Install GNU Sed: http://bugs.php.net/fix.php?id=26940&r=gnused Floating point limitations: http://bugs.php.net/fix.php?id=26940&r=float
