Distinguish between ASCII and Binary

What could be an elegant way to distinguish an ASCII file from a Binary one? Specifically, I'm working with STL files that can be both, and I need a solution how to seperate those two

Thanks,

Tero

[Stephen23]

The elegent way is to read the file format description. Wikipedia gives an outline:

https://en.wikipedia.org/wiki/STL_(file_format)

Apparently STL text files must start with the string "solid", whereas STL binary files must NOT start with that string. So to know the difference, you just need to read the first five characters. And testing those five characters is easy in "an elegant way", certainly much faster and more elegant than parsing the entire file.

[Chris Hooper]

I read a claim that some binary .stl files can still begin with "solid". not sure if its true.

Answer 1

[Bruno Luong]

I don't know if it's an elegant way but I just test if any charater is > 255

fid = fopen(stlfilename,'rt');
if fid > 0
    try
        c = textscan(fid,'%s','delimiter','\n');
        fclose(fid);
    catch ME
        message = ME.message;
        h = errordlg(message);
        waitfor(h);
        OK = -2;
        return
    end
else
    OK = -2;
    message = 'Cannot open STL file';
    h = errordlg(message);
    waitfor(h);
    return
end

c = c{1};
c(cellfun(@isempty,c)) = [];
if max(cellfun(@max,c)) > 255
    % Binary
    ...
else
    % Ascii
    ...
end

[Tero]

Thank you, seems to be efficient as well; some 19 s for a file size of 500Mb. Will implement

[Ameer Hamza]

This test can produce false negatives. For example

fid = fopen('file.bin', 'w');
fwrite(fid, [65 66 67 68], 'uint8')
fclose(fid)

Test

fid = fopen('file.bin','rt');
c = textscan(fid,'%s','delimiter','\n');
fclose(fid);
c = c{1};
c(cellfun(@isempty,c)) = [];

Result

>> max(cellfun(@max,c)) > 255
ans =
  logical
   0

[Bruno Luong]

We are talking about STL file, that can be ascii/binary, no any binary file.

Answer 2

[DGM]

See also stlGetFormat() from stltools on the FEX:

https://www.mathworks.com/matlabcentral/fileexchange/51200-stltools