Bug #10351 Updated: Parsing problem with nested ? : structures

ID: 10351 Updated by: m.ford@lmu.ac.uk Reported By: dwilson@cae.wisc.edu Status: Open Bug Type: Feature/Change Request Operating System: Sun OS 5.7 PHP Version: 4.0.3pl1 New Comment: I think the key here is not precedence, but associativity. The ?: operator is listed as being left-associative which, I think, means your simplified example will be evaluated like this: (1 ? (1 ? "3" : "2") : 1) ? "1" : "0" which will, indeed, result in 1! A right-associative ?: would be grouped as you expected, like this: 1 ? (1 ? "3" : "2") : (1 ? "1" : "0") -- ergo, in C ?: must be right-associative!! (As a side-note, operator associativity is listed in the operator precedence table with no real explanation of what it means, or link to such explanation -- perhaps this should be made a documentation feature request?) Previous Comments: ------------------------------------------------------------------------ [2002-04-29 11:13:40] dwilson@cae.wisc.edu See comment starting with "I checked...". ------------------------------------------------------------------------ [2002-04-29 10:34:57] dwilson@cae.wisc.edu I checked, and < has a higher precedence than ?: as one would expect. For example, with $dHour = 5, this is equivalent to: $departmeals = 1 ? 1 ? "3" : "2" : 1 ? "1" : "0"; which should evaluate to "3" but evaluates to "1" instead. The C language has no trouble with this construction: sun-66% cat temp.c #include <stdio.h> main(){ printf("%s\n",1 ? 1 ? "3" : "2" : 1 ? "1" : "0"); } sun-66% cc temp.c sun-66% a.out 3 ------------------------------------------------------------------------ [2002-04-27 15:19:22] jimw@php.net it does execute correctly, given the relative precedence of the '<' and '?:' operators. ------------------------------------------------------------------------ [2001-04-16 16:14:48] dwilson@cae.wisc.edu The following statement does not execute correctly: $departmeals = $dHour < 10.5 ? $dHour < 6.0 ? "3" : "2" : $dHour < 18.0 ? "1" : "0"; No error message--it just returns the wrong result. It does execute correctly if parentheses are added: $departmeals = $dHour < 10.5 ? ($dHour < 6.0 ? "3" : "2") : ($dHour < 18.0 ? "1" : "0"); The original is not ambiguous; it should parse and execute correctly. ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=10351&edit=1