# Error while writing unformatted data to unformatted file
**URL:** https://fortran-lang.discourse.group/t/error-while-writing-unformatted-data-to-unformatted-file/11116
**Category:** Uncategorized
**Created:** [September 24, 2026, 7:00pm UTC](https://fortran-lang.discourse.group/t/error-while-writing-unformatted-data-to-unformatted-file/11116 "2026-09-24T19:00:21Z")
**Posts on this page:** 10
**Page:** 1
### Author:  [@Vahid](https://fortran-lang.discourse.group/u/Vahid)
#### Post date: [September 24, 2026, 7:00pm UTC](https://fortran-lang.discourse.group/t/error-while-writing-unformatted-data-to-unformatted-file/11116/1 "2026-09-24T19:00:21Z")
I am attempting to store DP data to a binary file as single precision. The DP data is inside multiple loops in a fortran code called EPW. When I format the data and create the binary file as formatted, the output.bin stores the desired data. However, when I try
```auto
open(newunit=file_unit, file='output.bin', status='replace', access='stream', form='unformatted')
```
and
```auto
temp_out=real(SQRT(g2),KIND=sp)
write(file_unit) temp_out
```
where temp\_out is a single-precision real, I get the following error:
```auto
unformatted I/O to unit open for formatted transfers, unit 0
```
But neither the data nor the file\_unit is formatted.
I would appreciate any suggestions as to how to avoid this error.
Thanks,
Vahid
---
### Author:  [@wspector](https://fortran-lang.discourse.group/u/wspector)
#### Post date: [September 24, 2026, 8:12pm UTC](https://fortran-lang.discourse.group/t/error-while-writing-unformatted-data-to-unformatted-file/11116/3 "2026-09-24T20:12:55Z")
Why is it attempting to write on unit 0 (`stderr`)? Somehow `file_unit` doesn’t have the correct unit number.
---
### Author:  [@Vahid](https://fortran-lang.discourse.group/u/Vahid)
#### Post date: [September 24, 2026, 8:39pm UTC](https://fortran-lang.discourse.group/t/error-while-writing-unformatted-data-to-unformatted-file/11116/4 "2026-09-24T20:39:43Z")
Thank you for taking the time to respond.I have declared file\_unit as an integer. I assumed that using “newunit” in the open statement would automatically assign a negative number to file\_unit. I checked this number after opening and before writing (AI suggestion) and it was -129.
Vahid
---
### Author:  [@jwmwalrus](https://fortran-lang.discourse.group/u/jwmwalrus)
#### Post date: [September 24, 2026, 8:45pm UTC](https://fortran-lang.discourse.group/t/error-while-writing-unformatted-data-to-unformatted-file/11116/5 "2026-09-24T20:45:14Z")
Which compiler are you using?
The `NEWUNIT=` feature should have picked an unused unit different from `INPUT_UNIT`, `OUTPUT_UNIT` or `ERROR_UNIT`, but it’s picking `ERROR_UNIT` instead.
(To avoid these kind of issues, compilers should assign a negative unused value to the `NEWUNIT=variable`)
You could try using an explicit unit number (e.g., `UNIT = 100`) to see what happens.
---
### Author:  [@urbanjost](https://fortran-lang.discourse.group/u/urbanjost)
#### Post date: [September 24, 2026, 8:45pm UTC](https://fortran-lang.discourse.group/t/error-while-writing-unformatted-data-to-unformatted-file/11116/6 "2026-09-24T20:45:39Z")
Is the OPEN in the same procedure/scope as where you write? When you said you checked it before the write did you check it at the line above the write or possibly in some other scope? Are you sure the error is from this write statement?
---
### Author:  [@Vahid](https://fortran-lang.discourse.group/u/Vahid)
#### Post date: [September 24, 2026, 8:52pm UTC](https://fortran-lang.discourse.group/t/error-while-writing-unformatted-data-to-unformatted-file/11116/7 "2026-09-24T20:52:45Z")
I am using the intel/2023.2.1 module on Rorqual cluster of AllianceCanada. Even though the EPW code was compiled with openmpi, I am running it serially.
Replacing file\_unit with 100 results in the following compilation error:
```auto
transport.f90(180): error #7838: A scalar default-integer variable is required in this context. [100]
open(newunit=100, file='output.bin', status='replace', access='stream', form='unformatted')
-----------------^
compilation aborted for transport.f90
```
---
### Author:  [@urbanjost](https://fortran-lang.discourse.group/u/urbanjost)
#### Post date: [September 24, 2026, 8:56pm UTC](https://fortran-lang.discourse.group/t/error-while-writing-unformatted-data-to-unformatted-file/11116/8 "2026-09-24T20:56:35Z")
when using a fixed value it is UNIT=100 not NEWUNIT=100
---
### Author:  [@Vahid](https://fortran-lang.discourse.group/u/Vahid)
#### Post date: [September 24, 2026, 8:57pm UTC](https://fortran-lang.discourse.group/t/error-while-writing-unformatted-data-to-unformatted-file/11116/9 "2026-09-24T20:57:57Z")
The opening is done inside the first outer loop. The structure is as follows:
```auto
1. Outermost loop 1 in file ephwann_shuffle.f90
2. the above calls transport.f90 where the opening and printing is done
3. For first index of loop 1 in transport.f90, open the binary file
4. Three other loops in transport.f90
5. write in the innermost loop
```
---
### Author:  [@Vahid](https://fortran-lang.discourse.group/u/Vahid)
#### Post date: [September 24, 2026, 9:07pm UTC](https://fortran-lang.discourse.group/t/error-while-writing-unformatted-data-to-unformatted-file/11116/10 "2026-09-24T21:07:28Z")
Using Unit=100 did the trick. The code printed the data to binary file.
Thank you for all the help.
---
### Author:  [@urbanjost](https://fortran-lang.discourse.group/u/urbanjost)
#### Post date: [September 24, 2026, 10:44pm UTC](https://fortran-lang.discourse.group/t/error-while-writing-unformatted-data-to-unformatted-file/11116/11 "2026-09-24T22:44:07Z")
From your description it sounds like all the I/O is in one routine but that the routine is called multiple times, possibly expecting the LUN unit code to be remembered between calls. But Fortran is not required to save a value between calls unless it has the SAVE attribute or the variable in defined in a module or common block used by the routine. If that reading of your description is correct you need to add the SAVE attribute when defining the FILE\_UNIT variable to ensure it retains its value. For example:
```
integer,save :: file_unit
```
Using a fixed value is useful because you do not have to pass the variable or give it a global or saved attribute; it has the drawback the it might collide with other procedures using the file for a different purpose. The value of NEWUNIT is that Fortran does the bookkeeping on what numbers are used already so you can be ensured the number you get back is not in use anywhere else.
The values returned by NEWUNIT are negative and less than -1 (A magic number specifying an error occurred on the OPEN) so there is no conflict with units the user specifies directly as you are doing, which all have to be positive values. So even though it is working now you might want to work through getting a value returned by NEWUNIT to understand the nuances of the feature better.