14-09-2010, 03:39 PM
The rule requires that the expression should be guaranteed to have the same value regardless of the order in which the operands within the expression are evaluated. This usually means no more than one volatile access occuring in the expression. All of the examples given in your original posting are compliant with the rule because the value is independent of the evaluation order, even x = v + v because + is commutative.
The recommendation that simple assignments should be used is intended to be restricted to simple assignments of the form x = v and not "simple assignments" according to the ISO definition. However, the recommendation does not have to be followed in order to be compliant with the rule. You should implement the rule (the value should be independent of the evaluation order) for compliance purposes and you might choose to issue a warning for non-simple assignments or you might choose to ignore them.
The recommendation that simple assignments should be used is intended to be restricted to simple assignments of the form x = v and not "simple assignments" according to the ISO definition. However, the recommendation does not have to be followed in order to be compliant with the rule. You should implement the rule (the value should be independent of the evaluation order) for compliance purposes and you might choose to issue a warning for non-simple assignments or you might choose to ignore them.
Posted by and on behalf of the MISRA C Working Group