4 byte or 8 bytes confusion

I'm reading a binary file and in the binary file I have integer and real arrays which are supposed to be 8 byte integers as in the documentation concerning the binary file.

So, I have the follwoing code;

integer*8 geom_data(512) !Declaration of array to be read from the binary file

open(unit=1,file=my_file_name,status='old',form='unformatted',access='direct',recl=512*8)

read(1,rec=record_no)geom_data

.......
     

This works ok.

But now after testing several test cases, I'm encountering a couple of test cases where the binary file has the integer and real arrays of 4 bytes.

So, the above code reads correctly if I have:

integer*4 geom_data(512) !Declaration of array to be read from the binary file

open(unit=1,file=my_file_name,status='old',form='unformatted',access='direct',recl=512*4 

That is, I declare geom_data as 4 bytes. Can anyone help/advise such that the reading is done correctly whether the integer happens to be 8 or 4 bytes in the binary file?

Please help..

Christy

Can anyone please help?

Christy,

does all the files have the same amount of arrays? If yes, you can see if they are 4-bytes or 8-bytes from the file size (use file_size@). If not, you can at least see that they are 4-bytes in the case that the file size is not a manifold of 8*512 (in other words, you have an odd amount of 4-bytes arrays).

Is it possible to read a file first as 4-bytes and then check whether the entries are OK? Then, if not, close the file and open it again as 8-bytes.

Hope this helps a little...

Regards - Wilfried

Wilfried,

Thank you for the response..

1. If I read as 8 bytes first-it reads some junk/incorrect values. But I do not have any means to verify in the code that the value is a junk.

2. I did not get about file size.Can you give an example?

Christy

Christy,

(1) ... and if you first read 4 bytes, can you then see if the values seem to be OK?

(2) Example: call file_size@(my_file,fsize,err_code) with characternn my_file, integer4 fsize and integer*2 err_code.

Regards - Wilfried

Hi wilfred, Thanks a lot- I was unwell for 3 days.

1)Thanks for that. Yes, if I read 4 bytes first and the intgers and reals are 8 bytes- I do get an error.

Can you tell me how should the statement be to detect the error (currently the program crashes)? Shall be grateful if helped.

Regards,Christy

Christy,

it might be possible in a way like this:

open(  ... as 4 bytes ...  )
read(...)

! test if the values are OK.
! If not, or if the read command fails:

close(...)
open(  ... as 8 bytes ...  )
read(...)

Hope that helps. Regards - Wilfried

Thanks Wilfred..yes- but how to test that a read command fails?

Christy,

the Fortran READ can include an error check. I take the example from your first posting here:

open(unit=1,file=my_file_name,status='old',form='unformatted',access='direct',recl=512*4,err=4711)
...
...
4711 print*,'error reading input file'

The entry 'err=4711' means that in case of an error the programme jumps to label 4711.

If you don't get this situation, the programm will give you 512 values à 4 bytes per line. Then check whether these values seems to be OK.

Regards - Wilfried