reading a binary file into matlab

I am ruining the following to codes

filelist = dir('E:\4_models\model1');
nt = size(filelist,1);
nx = 508;
ny = 637;
dx = 50;
dy = 50;
zdata = zeros(ny,nx,nt);
for i = nt
    fname = filelist(i).name;
    a = readcartesiangrid(fname);
    contourf(a.x, a.y, a.z, 31);
    colorbar
    daspect([1 1 1]);
    pause(0.1)
    z = a.z;
    zdata(:,:,i) = z;
end
for i = 2:nt
    z1 = zdata(:,:,1);
    zi = zdata(:,:,i);
    zd = zi - z1;
    imagesc(zd);
    colorbar
    set(gca,'Ydir','normal')
    caxis([0 35]);
    axis('equal')
    pause(0.2)
end
function [ grid ] = readcartesiangrid(fname, nx, ny, dx, dy )
fid = fopen('fname');
version = fread(fid, 1, 'uint32');
assert(version == 2, sprintf('Invalid file version: expected 2, got %i', version));

fclose(fid);

when I execute these two codes, I am getting the following error;

Invalid file identifier. Use fopen to generate a valid file identifier

Error in readcartesiangrid (line 17)
version = fread(fid, 1, 'uint32');

Answer 1

[James Tursa]

This line

fid = fopen('fname');

trys to open a file that is named exactly 'fname', which is not what you want. You probably want this:

fid = fopen(fname);

[Abdul Wahab]

Thanks a lot.This helped!!

Answer 2

[OCDER]

I think there're other issues despite fixing fid = fopen(fname)

 filelist = dir('E:\4_models\model1');
 filelist = filelist(~[filelist.isdir]); %You have a /. and /.. folder that needs to be skipped
 nt = size(filelist,1); %this gives you 1 number.
 ...
 for i = nt %this will only do the last file.  Do  you want " for i = 1:nt " instead?
    fname = filelist(i).name; %this gives you only the file name, without the file path (ex: model2.mat)
    fname = fullfile(filelist(i).folder, filelist(i).name); %this gives you the full file path (ex: E:\4_models\model1\model2.mat)
    ...
 end

In your readcartesiangrid, recommend the following changes:

 fid = fopen(fname);
 assert(fid ~= -1, 'Error opening the file "%s".', fname) %Add check here to help with debugging

[Abdul Wahab]

This helped as well. Thank you for the detailed comment!!!