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Distinguish between ASCII and Binary

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Tero
Tero on 5 Nov 2020
Answered: DGM on 25 Mar 2024
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
  2 Comments
Stephen23
Stephen23 on 5 Nov 2020
Edited: Stephen23 on 5 Nov 2020
The elegent way is to read the file format description. Wikipedia gives an outline:
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
Chris Hooper on 25 Mar 2024
I read a claim that some binary .stl files can still begin with "solid". not sure if its true.

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Accepted Answer

Bruno Luong
Bruno Luong on 5 Nov 2020
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
  3 Comments
Ameer Hamza
Ameer Hamza on 5 Nov 2020
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
Bruno Luong on 5 Nov 2020
We are talking about STL file, that can be ascii/binary, no any binary file.

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More Answers (1)

DGM
DGM on 25 Mar 2024
See also stlGetFormat() from stltools on the FEX:

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