Re: size_t, casting and expression is always true (or false)

On 1 February 2011 15:07, Andrey Hristov <php@hristov.com> wrote: >  Hi Richard, > On 02/01/2011 02:35 PM, Richard Quadling wrote: >> Hi. >> >> I was looking at the cause for a test failing. >> >> It came down to ... >> >> size_t n; >> >> if (n < 0) { >>  // Code never reached as n is unsigned and cannot be negative. >> } >> >> >> I'm not a strong c developer, but from reading it seems that size_t is >> always unsigned. >> >> Using the windows compiler (and turning on all the warnings via /Wall >> though /W4 should be enough), this warning reports as ... >> >> xxx\yyy.c(nnn) : warning C4296: '>=' : expression is always false >> >> I then ran a full build and extracted all the C4926 warnings. >> >> main\network.c(1175) : warning C4296: '>=' : expression is always true >> main\streams\filter.c(363) : warning C4296: '<' : expression is always false >> main\streams\streams.c(921) : warning C4296: '>=' : expression is always true >> ext\mysqlnd\mysqlnd.c(1006) : warning C4296: '>=' : expression is always true >> ext\mysqlnd\mysqlnd.c(1031) : warning C4296: '>=' : expression is always true >> ext\mysqlnd\mysqlnd_loaddata.c(215) : warning C4296: '<' : expression >> is always false >> ext\mysqlnd\mysqlnd_loaddata.c(223) : warning C4296: '<' : expression >> is always false >> ext\mysqlnd\mysqlnd_ps.c(1480) : warning C4296: '<' : expression is always >> false >> ext\mysqlnd\mysqlnd_ps.c(1620) : warning C4296: '<' : expression is always >> false >> ext\standard\ftp_fopen_wrapper.c(645) : warning C4296: '>=' : >> expression is always true >> ext\standard\image.c(645) : warning C4296: '<' : expression is always false >> ext\standard\streamsfuncs.c(637) : warning C4296: '>=' : expression is >> always true >> ext\standard\streamsfuncs.c(677) : warning C4296: '>=' : expression is >> always true >> ext\standard\var.c(403) : warning C4296: '<' : expression is always false >> ext\pdo\pdo_stmt.c(463) : warning C4296: '<' : expression is always false >> ext\soap\php_encoding.c(2794) : warning C4296: '<' : expression is always >> false > > which mysqlnd/PHP sources did you use in your build? > >> In the case of the bug [1], the incorrect type comparison resulted in >> the suppression of an error which cased the test to fail, leading me >> here. >> >> I think other comparisons in the above list are also suppressing >> errors (I think mysqlnd will fail to report a loss of connection >> during mysqlnd_handle_local_infile() for example). >> >> Regards, >> >> Richard. >> >> [1] http://bugs.php.net/bug.php?id=49072 >> > > Best, > Andrey > php-src/branches/PHP5_3/ext/mysqlnd I've not run the code or any tests. I was just commenting on the parallels between bug#49072 and the code that is being reported. Richard. -- Richard Quadling Twitter : EE : Zend @RQuadling : e-e.com/M_248814.html : bit.ly/9O8vFY