https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107031
Bug ID: 107031
Summary: endfile truncates file at wrong position
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: kishore96 at gmail dot com
Target Milestone: ---
SUMMARY
-------
When `endfile` is used to truncate a file after a read statement, gfortran
wrongly inserts end-of-file after the next line, rather than after the current
line.
STEPS TO REPRODUCE
------------------
1. create the following program, truncate.f90:
```fortran
program test_truncate
integer :: num_rec, tmp, i, ioerr
open(1, file="in.dat", action='readwrite')
num_rec = 5
i = 1
ioerr = 0
do while (i <= num_rec .and. ioerr == 0)
read(1, *, iostat=ioerr) tmp
i = i+1
enddo
!backspace(1)
endfile(1)
close(1)
end program test_truncate
```
2. Create the following text file, `in.dat`
```
1
2
3
4
5
6
7
8
9
10
```
3. Compile the program: `gfortran truncate.f90`
4. Run the program: `./a.out`
OBSERVED RESULTS
----------------
```bash
$cat in.dat
1
2
3
4
5
6
```
EXPECTED RESULTS
----------------
```bash
$cat in.dat
1
2
3
4
5
```
Since after the end of the loop, the current record is `5`, one would expect
endfile to write an end-of-file record as the next record (e.g.
<https://docs.oracle.com/cd/E19957-01/805-4939/6j4m0vn8v/index.html>), leading
to the result above.
SOFTWARE VERSIONS
-----------------
OS: Arch Linux
gfortran: 12.2.0
ADDITIONAL INFORMATION
----------------------
Intel ifort (version 19.0.5.281 20190815) produces the expected result.
May be related to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52387, but I
think not, since my example program doesn't use nonadvancing reads anywhere.
Uncommenting the `backspace(1)` gives output
```bash
$cat in.dat
1
2
3
4
```
