Question about fgetl function

Question

Diego 2012-11-13

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/53621-question-about-fgetl-function

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

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Answer 1

Walter Roberson 2012-11-13

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https://ww2.mathworks.cn/matlabcentral/answers/53621-question-about-fgetl-function#answer_65256

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.