Problem after reading binary file with windows gfortran

Compilers
3

Hi,

I have encountered the exact same behavior.

W11, gcc 15.2 with mingw64 13.0.0

Reading and closing a formatted file is fine
Reading and closing an unformatted file is fine

After an unformatted file has been read (even for only one value) though, fractional parts of any future formatted reads are being dropped (eg : ‘31649.08’ will be read as ‘31649.00’)

(If the unformatted file is only opened, but immediately closed without reading any value, then the problem does not appear)

Adding DECIMAL=’POINT’ to the formatted OPEN statement and/or the READ statement does not solve the issue.

Specifying the format (eg (F15.8)) in the READ statement does not solve the issue.

If the content of the formatted file is written in exponential form, then there is no issue.

Additionally, the issue only manifests itself when executing directly on Windows. If the exact same executable is launched by gdb (on Windows), then the issue is not present.

Here is a minimum example to reproduce :slight_smile:

subroutine readtxt
t=0.0
open(newunit=kf,file=“toto.txt”,form=‘FORMATTED’,
& status=‘OLD’,action=‘READ’,iostat=IPB)
print*,‘IPB=’,IPB
if (IPB==0) then
read(kf,*) t
print*,‘t=’,t
endif
close(kf)
return
end

subroutine readbin
OPEN(newunit=io,FILE=“toto.bin”,ACCESS=‘STREAM’,
& FORM=‘UNFORMATTED’,STATUS=‘OLD’,IOSTAT=IPB)
read(io) x
close(io)
return
end

program toto
call readtxt
call readtxt
call readbin
call readtxt
call readtxt
return
end

With toto.txt being a simple one line ASCII file with eg 123.456 written in it, and toto.bin any non-empty binary file.

The end result produces the following output on Windows :

PS D:\Work\toto> .\a.exe

IPB= 0

t= 123.456001

IPB= 0

t= 123.456001

IPB= 0

t= 123.000000

IPB= 0

t= 123.000000