Re: logical AND assignments

On Tue, Sep 07, 2010 at 10:41:46PM -0400, Robert E. Glaser wrote: > My ISP upgraded his server from Ubuntu 9.04 to Ubuntu 9.10, which > probably included a newer PHP version. I don't know what PHP version > was on previously. Code I've had running for years broke, and I tracked > it down to this equivalent: > > <?php > > echo 'Current PHP version: ', phpversion(), "<br><br>"; > > $Condition0 = true and false; > If ($Condition0) > echo "Condition0<br>"; > else echo "Not Condition0<br>"; > > $Condition1 = false and true; > If ($Condition1) > echo "Condition1<br>"; > else echo "Not Condition1<br>"; > > $Condition2 = (true and false); > If ($Condition2) > echo "Condition2<br>"; > else echo "Not Condition2<br>"; > > $Condition3 = true && false; > If ($Condition3) > echo "Condition3<br>"; > else echo "Not Condition3<br>"; > > $Condition4 = (true && false); > If ($Condition4) > echo "Condition4<br>"; > else echo "Not Condition4<br>"; > ?> > > which returns: > > Current PHP version: 5.2.10-2ubuntu6.4 > > Condition0 > Not Condition1 > Not Condition2 > Not Condition3 > Not Condition4 > > =============================== > > I added parentheses around the offending line of code and it seems okay > now. But I am stymied as to why they're required at all. They never > were before, and as far as I see there is no PHP requirement to include > the parentheses. Have I done something silly? Mostly I'm worried if > there are any other changes I need to make. I searched my code and > hopefully found all similar instances, but who really knows about those > kinds of things? > > Any comments? I can't tell what (if anything) changed or why. But the problem appears to rest with the fact that "&&" is higher precedence than "=", and "and" is lower precedence. Here are two references: http://us.php.net/manual/en/language.operators.logical.php http://us.php.net/manual/en/language.operators.precedence.php It's tricky, I'll admit. Since I normally mean for things I'm logically "anding" to be "anded" before any other operation, it's forced me to change almost all my "ands" to "&&". Just so I don't make a mistake. Also note the "associativity" in the second reference. Paul -- Paul M. Foster