Re: [patch, libgfortran] Part 2: PR105456 Child I/O does not propage iostat

[Steve Kargl <sgk@troutmask.apl.washington.edu>]

On Thu, Feb 29, 2024 at 10:28:19AM -0800, Jerry D wrote:
> On 2/29/24 10:13 AM, Steve Kargl wrote:
> > On Thu, Feb 29, 2024 at 09:36:43AM -0800, Jerry D wrote:
> > > On 2/29/24 1:47 AM, Bernhard Reutner-Fischer wrote:
> > > 
> > > > And, just for my own education, the length limitation of iomsg to 255
> > > > chars is not backed by the standard AFAICS, right? It's just our
> > > > STRERR_MAXSZ?
> > > 
> > > Yes, its what we have had for a long lone time. Once you throw an error
> > > things get very processor dependent. I found MSGLEN set to 100 and IOMSG_len
> > > to 256. Nothing magic about it.
> > > 
> > 
> > There is no restriction on the length for the iomsg-variable
> > that receives the generated error message.  In fact, if the
> > iomsg-variable has a deferred-length type parameter, then
> > (re)-allocation to the exact length is expected.
> > 
> >    F2023
> > 
> >    12.11.6 IOMSG= specifier
> > 
> >    If an error, end-of-file, or end-of-record condition occurs during
> >    execution of an input/output statement, iomsg-variable is assigned
> >    an explanatory message, as if by intrinsic assignment. If no such
> >    condition occurs, the definition status and value of iomsg-variable
> >    are unchanged.
> > character(len=23) emsg
> > read(fd,*,iomsg=emsg)
> > 
> > Here, the generated iomsg is either truncated to a length of 23
> > or padded with blanks to a length of 23.
> > 
> > character(len=:), allocatable :: emsg
> > read(fd,*,iomsg=emsg)
> > 
> > Here, emsg should have the length of whatever error message was
> > generated.
> > HTH
> > 
> 
> Well, currently, if someone uses a larger string than 256 we are going to
> chop it off.
> 
> Do we want to process this differently now?
> 

If I look at the interfaces for UDTIO in F2023 (pp. 254-255),
the declaration for iomsg is

  CHARACTER (LEN=*), INTENT(INOUT) :: iomsg

F2023 (p. 62) has 
  An asterisk as a type-param-value specifies that a length type
  parameter is an assumed type parameter.  It is used for a dummy
  argument to assume the type parameter value from the effective
  argument, ...

So, in theory, one should be able to get the required length
from length from the argument.

  CHARACTER(LEN=23) str
  WRITE(6,'(DT)',iomsg=str) derived-type-entity

If the subroutine supplied by the user internally creates
an error message with 300 characters, then from the above I 
would think that it will be truncated to 23 characters.
OTOH, if the user is expecting the full 300 characters with

  CHARACTER(LEN=300) str
  WRITE(6,'(DT)',iomsg=str) derived-type-entity

then truncating internally to 256 seems wrong.

Now, that I looked at the interface more closely, the declaration

  CHARACTER (LEN=*), INTENT(INOUT) :: iomsg

seems to block the use of an unallocated deferred-length 'str'
and (re)-allocation does not occur.

 

-- 
Steve