To: J3                                                     J3/21-102r2
From: R. Bader & Bill Long
Subject: CFI_setpointer interpretation request F18/024
Date: 2021-March-05
Reference: 18-007r1

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NUMBER: F18/024
TITLE:  CFI_setpointer with result a deferred length character
KEYWORDS: C interoperability
DEFECT TYPE: Erratum
STATUS: Submitted


QUESTION:

Is the requirement in CFI_setpointer that the elem_lem member have the
same value in the source and result arguments intended to apply if the
result is of type CHARACTER with the length parameter deferred?

ANSWER:

No. It is an oversight in the standard that this rule apply to the case
of result being of type CHARACTER and having the length parameter
deferred.

Currently in section 18.5.5.9 "The CFI_setpointer function" states in
para 2 that

"If source is not a null pointer, the corresponding values of the
elem_len, rank, and type members shall be the same in the C
descriptors with the addresses source and result."

The function can therefore not work correctly if the "result"
parameter is a descriptor address for a deferred-length character
entity coming in from Fortran, because the elem_len value is not
available. Manual updates to result->elem_len are prohibited by 18.6
para 1.

The CFI_setpointer function in the intrinsic module ISO_C_BINDING is
intended to provide a means for C programmers to replicate the pointer
association capability in Fortran, for dummy arguments in interfaces
with with interoperable interfaces. Thus, for the case of a character
result having deferred length, which is allowed at [478:21], the
correct action should be for the elem_len value from the source to be
copied to the same member of result as part of execution of the
function.

Edits are supplied to correct this defect.


EDITS to 18-007r1:

In 18.5.5.9 The CFI_setpointer function

- [491:27] In the description of the source formal parameter, second
  sentence, delete "elem_len, ".

- [491:28+] In the description of the source formal parameter, after
  the second sentence add new sentence:

  "If source is not a null pointer and the C descriptor with the
  address result does not describe a deferred length character
  pointer, the corresponding values of the elem_len member shall be
  the same in the C descriptors with the addresses source and result."

- [491:31] In the first sentence of paragraph 3, "Description" replace
  "base_addr and dim" by "base_addr, dim and possibly elem_len".

- [491:38] At the end of the second bullet point of paragraph 3,
  "Description", add new sentence;

  "If the C descriptor with the address result describes a character
  pointer of deferred length, the value of its elem_len member is set
  to source->elem_len".


SUBMITTED BY: Reinhold Bader

HISTORY: 21-102r1  m223  F18/024 Submitted
         21-102r3  m233  Paper passed.

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