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3675. std::ios_base::iword/pword might be misspecified

Section: 31.5.2.6 [ios.base.storage] Status: New Submitter: Jiang An Opened: 2022-02-14 Last modified: 2022-03-04

Priority: 4

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Discussion:

Currently 31.5.2.6 [ios.base.storage] p5 and p8 say "On failure, a valid long&/void*& initialized to 0". Such wording seems wrong, because a long&/void*& variable or return value can't be initialized with 0. And the values of referenced objects may be underspecified, because an implementation may reuse the same long/void* objects on failure, and thus it's insufficient to specify the initial values of these objects only.

[2022-03-04; Reflector poll]

Set priority to 4 after reflector poll.

Proposed resolution:

This wording is relative to N4901.

1. Modify 31.5.2.6 [ios.base.storage] as indicated:

   long& iword(int idx);
   

   -3- […]

   -4- […]

   -5- Returns: On success iarray[idx]. On failure, an valid lvalue of type long& with value 0Linitialized to 0.

   void*& pword(int idx);
   

   -6- […]

   -7- […]

   -8- Returns: On success parray[idx]. On failure, an valid lvalue of type void*& with a null pointer valueinitialized to 0.

   -9- Remarks: After a subsequent call to pword(int) for the same object, the earlier return value may no longer be valid.