Determine number of bytes in a line of a binary file Matlab - matlab

Question

I am working on importing some data interpretation of binary files from Fortran to MATLAB and have come across a bit of an issue.
In the Fortran file I am working with the following check is performed
CHARACTER*72 PICTFILE
CHARACTER*8192 INLINE
INTEGER NPX
INTEGER NLN
INTEGER BYTES
c This is read from another file but I'll just hard code it for now
NPX = 1024
NLN = 1024
bytes=2
open(unit=10, file=pictfile, access='direct', recl=2*npx, status='old')
read(10,rec=nln, err=20) inline(1:2*npx)
go to 21
20 bytes=1
21 continue
close(unit=10)
where nln is the number of lines in the file being read, and npx is the number of integers contained in each line. This check basically determines whether each of those integers is 1 byte or 2 bytes. I understand the Fortran code well enough to figure that out, but now I need to figure out how to perform this check in MATLAB. I have tried using the fgetl command on the file and then reading the length of the characters contained but the length never seems to be more than 4 or 5 characters, when even if each integer is 1 byte the length should be somewhere around 1000.
Does someone know a way that I can automatically perform this check in MATLAB?

Answer 1

So what we figured out was that the check is simply to see if the file is the correct size. In Matlab this can be done as
fullpath=which(file); %extracting the full file path
s=dir(fullpath); %extracting information about hte file
fid=fopen(file_name,'r'); %opening image file
if s.bytes/NLN==2*NPX %if the file is NLN*NPX*2 bytes
for n=1:NLN %for each line
dn(n,:) = (fread(fid, NPX, '*uint16','b'))'; %reading in lines into DN
end
elseif s.bytes/NLN==NPX %Else if the file is NLN*NPX bytes
for n=1:NLN %for each line
dn(n,:) = (fread(fid, NPX, '*uint8','b'))'; %reading in lines into DN
end
else %If the file is neither something went wrong
error('Invalid file. The file is not the correct size specified by the SUM file')
end
where file contains the filename, nln contains the number of lines, and npx contains the number of columns. Hope this helps anyone who may have a similar answer, but be warned because this will only work if your file only contains data that has the same number of bytes for each entry, and if you know the total number of entries there should be!

Answer 2

Generally speaking, binary files don't have line lengths; only text files have line lengths. MATLAB's getl will read until it finds the binary equivalent of newline characters. It then removes them and returns the result. The binary file, on the other hand, should read a block of length 2*npx and return the result. It looks like you want to use fread to get a block of data like this:
inline = fread(fileID,2*npx)
Your fortran code is requesting to read record nln. If the code you have shared reads all the records starting at the first one and working up, then can just put the above code in a loop for nln=1:maxValue. However, if you really do want to yank out record nln you need to fseek to that position first:
fseek(fileID, nln*2*npx, -1);
inline = fread(fileID,2*npx)
so you get something like the following:
Either reading them all in a loop:
fileID = fopen(pictfile);
nln = 0;
while ~feof(fileID)
nln = nln+1;
inline = fread(fileID,2*npx);
end
fclose(fileID);
or picking out only the number `nln record:
fileID = fopen(pictfile);
nln = 7;
fseek(fileID, nln*2*npx, -1);
inline = fread(fileID,2*npx);
fclose(fileID);