Read and process a Fortran90 binary file

Hi,

I have a Fortran90 code where a variable called 'stream' is defined such that it stores certain variable every nstep:

open(19,file='stream',form='UNFORMATTED',position='append')
if(mod(NSTEP,100).eq.0)then
    write(19)NSTEP,U,W,zeta
    endif

How can I properly read the file in Matlab for postprocessing?

FYI, the fortran code is built with double precision.

Thank you

[James Tursa]

Unformatted Fortran can contain beginning and end of line markers in the file. You need to give us a small sample file to work with to verify this, and also tell us the type and dimensions of the variables NSTEP, U, W, and zeta.

[Walter Roberson]

The FORTRAN runtime system embeds the record boundaries in the data by inserting an INTEGER*4 byte count at the beginning and end of each unformatted sequential record during an unformatted sequential WRITE. The trailing byte count enables BACKSPACE to operate on records.

https://docs.oracle.com/cd/E19957-01/805-4939/6j4m0vnc4/index.html

[Carola Forlini]

I am attaching an extract of the file.

NSTEP is an integer = 2000

U, W, zeta are matrices = 32x512

Thank you

Answer 1

[Les Beckham]

It would help to have a sample file to experiment with.

Nevertheless, assuming that the write call that you have shown is the only thing that writes to this file in your Fortran code, I would suggest something like this using fread and reshape:

fid = fopen('your_file_name.ext', 'rb');
A = fread(fid);
data = reshape(A, 4, numel(A)/4)';
nstep = A(:,1);
U = A(:,2);
W = A(:,3);
zeta = A(:,4);

Note that you might run into endian-ness issues if your Fortran code runs on a different architecture than your Matlab is running on. See the documentation for the machinefmt option to fread if necessary.

[Walter Roberson]

form='UNFORMATTED' has record length markers before and after each record.

[Walter Roberson]

If you start with fread(fid, 1, 'integer*4') and discard that, and thereafter fread() with a skip field of 8 then it should be properly positioned to fread() more.

Unfortunately we are not told the size of NSTEP, U, W, zeta

[Carola Forlini]

Hi, I provided a sample file and the dimensions of NSTEP, U, W, zeta in the post above.

Thank you.

[Les Beckham]

Thanks for adding the example.

Can you clarify what you mean by this?

NSTEP is an integer = 2000

Especially the "= 2000" part. Is that just an example of a possible value? What is the size of this integer (number of bits)?

Also, are U, W, and zeta double precision (64 bit) floating point 2-d arrays with the given size?