MATLAB: Question about fgetl function

fgetl

Dear all,
I'm learning to use fgetl and had followed the example that appears in the documentation:
fid = fopen('SomeFile.xxx');
tline = fgetl(fid);
while ischar(tline)
  disp(tline)
  tline = fgetl(fid);
end
fclose(fid);
The example works great, but I don't understand why I have to declare the tline again inside the loop.
If I don't do that it keeps looping for ever!
Can somebody explain me the reason?
Thanks,
Diego

Best Answer

When you use tline = fgetl(fid) before the loop, that does not define tline to be an active function that returns the next line every time it is referenced. Instead, that statement reads a line once and assigns the line to tline as a string. In order to advance to the next line, you need to call fgetl() again. tline = fgetl(fid) is not a declaration: it is an assignment in which a current value is saved to a variable; in order to update the value, the function fgetl() needs to be called again.
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