Read a binary array with mixed types - octave

Question

I am writing a function similar to this to read in binary formatted .ply files.
The linked function reads the header and the skips to the binary array, reading that in with numpy and I would like to do the same in Octave.
My code for reading the header is
fid = fopen('/path/to/file.ply');
tline = fgetl(fid); % read first line
len = 0;
prop = {};
dtype = {};
fmt = 'binary';
while ~strcmp(tline, "end_header")
len = len + length(tline) + 1; % increase header length, +1 includes EOL
tline = strsplit(tline); % split string
if strcmp('format', tline{1}) && strcmp('ascii', tline{2}) % test whether file is ascii
fmt = 'ascii';
end
if strcmp('element', tline{1}) && strcmp('vertex', tline{2}) % number of points
N = tline{3};
end
if strcmp('property', tline{1}) % identify fields
dtype = [dtype, tline{2}];
prop = [prop, tline{3}];
end
tline = fgetl(fid);
end
len = len + length(tline) + 1; % add 'end_header' to len
So I have arrays of data types
dtype =
{
[1,1] = float
[1,2] = float
[1,3] = float
[1,4] = int
[1,5] = int
[1,6] = int
[1,7] = float
[1,8] = float
[1,9] = float
}
and I know the shape of the array.
N = 61415
Is there a function that replicates numpy's fromfile and can I seek to the right location in my file (I know where the binary data starts in the file as I have len)
Following #tasos-papastylianou answer I tried
fseek(fid, len);
fread(fid, 3, 'float')
Which returns the correct 3 values, but the next value is an integer and therefore gives the incorrect answer.
fread(fid, 4, 'float')
arr =
-1.4298e+00
-5.3943e+00
1.6623e+01
1.5274e-43 <<<< should be 109
My solution
function pts = read_ply(fn)
fid = fopen(fn);
tline = fgetl(fid); % read first line
len = 0;
prop = {};
% dtype_map = {'float': 'f4', 'uchar': 'B', 'int':'i'}
dtype = {};
fmt = 'binary';
while ~strcmp(tline, "end_header")
len = len + length(tline) + 1; % increase header length, +1 includes EOL
tline = strsplit(tline); % split string
if strcmp('format', tline{1}) && strcmp('ascii', tline{2}) % test whether file is ascii
fmt = 'ascii';
elseif strcmp('element', tline{1}) && strcmp('vertex', tline{2}) % number of points
N = str2num(tline{3});
elseif strcmp('property', tline{1}) % identify fields
dtype = [dtype, tline{2}];
prop = [prop, tline{3}];
endif
tline = fgetl(fid);
endwhile
len = len + length(tline) + 1; % add 'end_header
% total file length minus header
fseek(fid, 0, 1);
file_length = ftell(fid) - len;
types = struct('float', 4, 'int', 4, 'float64', 8);
pts = struct();
seek_plus = 0;
for i = 1:length(prop)
fseek(fid, len + seek_plus);
dt = types.(dtype{i}); % dtype for field
pts.(prop{i}) = fread(fid, N, dtype{i}, int32(file_length / N) - dt);
seek_plus = seek_plus + dt;
endfor
This does not answer my original question as it involves a loop, but it seems fairly efficient. Arrays can be constructed as so.
xyz = [pts.x, pts.y, pts.z];

Answer 1

Your question confuses me a bit towards the end, since the most direct equivalent to numpy's saving an array in a numpy-specific binary format is octave's save which saves an array to an octave-specific binary format.
Having said that, this doesn't sound like what you want so I'm assuming the fromfile reference is a red herring.
In general if you have a binary file you want to open, read, or seek (i.e. place the cursor at a particular position), you can use the fopen, fread, and fseek commands. Also useful, ftell, frewind, etc.
These are all fairly simple commands. Just have a look at their documentation in the terminal (e.g. help fseek ).