How to write to a text file several times without overwriting the old values

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Erik
Erik on 19 Sep 2011
I write the output values from a simulation to a txt file using.
outputFile = fopen('output.txt','w'); fprintf(outputFile,'values');........
I would like to run the simulation several times with different output and store each simulation output without overwriting the old values. Is there some easy way to append the old values?

Answers (3)

Tigersnooze
Tigersnooze on 19 Sep 2011
I think if you do
outputFile = fopen('output.txt', 'a+');
It would work when put in a loop. 'a' will append, where 'w' will discard existing contents.

the cyclist
the cyclist on 19 Sep 2011
One way:
for nf = 1:3
% Other stuff
outputFile = fopen(['output',num2str(nf),'.txt'],'w');
fprintf(outputFile,'values');
end
  1 Comment
the cyclist
the cyclist on 20 Sep 2011
I didn't read your question carefully enough. My method will create multiple output files, not one file with appended data.

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Walter Roberson
Walter Roberson on 19 Sep 2011
You want to append the old values after the new ones, or you want to append the new values after the old?
Appending the old values after the new requires opening the file with 'a+' access, seeking to the beginning of the file with fseek(fid,0,0), reading and recording the old values, seeking back to the beginning of the file, writing the new values, then writing the recorded old values. There is no built-in mechanism to "insert" text "moving over" the existing text automatically.
Appending the new values after the old values requires opening the file with 'a' or 'a+' access, and writing the new values. This is easier and more robust.

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