CWG2855 [expr.post.incr] has no integral promotion, [expr.pre.incr] has #479

Activity

1. leni536

   changed the title [-][expr.post.incr] has no integral promition, [expr.pre.incr] has[/-] [+][expr.post.incr] has no integral promotion, [expr.pre.incr] has[/+] on Dec 12, 2023
2. t3nsor commented on Dec 12, 2023

   

   t3nsor

   on Dec 12, 2023

   Last edited by t3nsor

   More actions

   Possible resolution:

   Edit [expr.post.incr]:

   The value of a postfix ++ expression is the value of its operand.
   [Note 1: The value obtained is a copy of the original value. — end note]
   The operand shall be a modifiable lvalue. The type of the operand shall be an arithmetic type other than cv bool, or a pointer to a complete object type. An operand with volatile-qualified type is deprecated; see [depr.volatile.type]. The value of the operand object is modified ([defns.access]) by adding 1 to it as if it were the operand of the prefix ++ operator. The value computation of the ++ expression is sequenced before the modification of the operand object. With respect to an indeterminately-sequenced function call, the operation of postfix ++ is a single evaluation.
   [Note 2: Therefore, a function call cannot intervene between the lvalue-to-rvalue conversion and the side effect associated with any single postfix ++ operator. — end note]
   The result is a prvalue. The type of the result is the cv-unqualified version of the type of the operand. If the operand is a bit-field that cannot represent the incremented value, the resulting value of the bit-field is implementation-defined. See also [expr.add] and [expr.ass].

   The operand of postfix -- is decremented analogously to the postfix ++ operator.
   [Note 3: For prefix increment and decrement, see [expr.pre.incr]. — end note]

   Edit [expr.pre.incr]:

   The operand of prefix ++ or -- is modified ([defns.access]) by adding 1. The operand shall be a modifiable lvalue. The type of the operand shall not be an arithmetic type other than of type cv bool, or a pointer to a completely-defined object type. An operand with volatile-qualified type is deprecated; see [depr.volatile.type]. The result is the updated operand; it is an lvalue, and it is a bit-field if the operand is a bit-field. The expression ++x is otherwise equivalent to x+=1 and the expression --x is otherwise equivalent to x-=1.
   [Note 1: See the discussions of addition and assignment operators for information on conversions. — end note]

   The operand of prefix -- is modified ([defns.access]) by subtracting 1. The requirements on the operand of prefix -- and the properties of its result are otherwise the same as those of prefix ++.
   [Note 2 1: For postfix increment and decrement, see [expr.post.incr]. — end note]
3. jensmaurer commented on Feb 3, 2024

   

   jensmaurer

   on Feb 3, 2024

   Member

   More actions

   CWG2855
4. jensmaurer

   changed the title [-][expr.post.incr] has no integral promotion, [expr.pre.incr] has[/-] [+]CWG2855 [expr.post.incr] has no integral promotion, [expr.pre.incr] has[/+] on Feb 3, 2024
5. pinskia commented on Feb 16, 2024

   

   pinskia

   on Feb 16, 2024

   More actions

   Hmm, this seems to make an C and C++ (defined) behavior different with represent to post increment. I would have hoped post increment still be well defined here too.
6. jensmaurer commented on Feb 16, 2024

   

   jensmaurer

   on Feb 16, 2024

   Member

   More actions

   @pinskia, could you please elaborate? The proposal is to have prefix and postfix increment/decrement have the same (well-defined) behavior by applying integral promotions in both cases.
7. pinskia commented on Feb 16, 2024

   

   pinskia

   on Feb 16, 2024

   More actions

   @pinskia, could you please elaborate? The proposal is to have prefix and postfix increment/decrement have the same (well-defined) behavior by applying integral promotions in both cases.

   Oh I read as the opposite for some reason, thanks for the carification there.
8. tkoeppe

   closed this as completedin draft#6906on Apr 15, 2024