how to amend an existing text file in a certain line and create new ones

Question

Christina 2011-9-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/16572-how-to-amend-an-existing-text-file-in-a-certain-line-and-create-new-ones

Hello all

I've got a text file and I need to change only one parameter of it many times (in a for loop).

Until now, I've located the line where my parameter is, I've changed it and NOW I NEED TO WRITE THE NEW PARAMETER IN A NEW TEXT FILE, WHOSE ONLY DIFFERENCE WITH THE PREVIOUS ONE WOULD BE THE DIFFERNT PARAMETER VALUES.

My code until now looks like that.

 %Define the range of the parameter sathh
 %Assume that sathh can vary between 0.01 and 0.05
 parameterA_range = 0.01:0.01:0.05;
 %The loop counter
 for i=1:length(parameterA_range)
 %Extract each value from the range of the parameterA_range
 param1 = parameterA_range(i)
 %Replicate each of these values 4 times (4 soil layers) and create the new
 %parameter set
 parameterA = repmat(param1,1,4)
 %Replace the parameterA with the new parameterA parameters.
 %Open the txt file and scan through it
 fid = fopen('sensanalysis3.txt');
 C = textscan(fid,'%s','delimiter','\n');
 %Find the line number 188, where the parameterA is            
 line188 = C{1}{188}
 line188_changed  =strrep(line188,'0.0453, 0.0453, 0.0453, 0.0453',num2str(sathh))

So, in line 188 I need to have the new values of parameterA.

Any ideas?

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Christina 2011-9-23

Correction: in the last command:

line188_changed =strrep(line188,'0.0453, 0.0453, 0.0453, 0.0453',num2str(parameterA))

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Answer 1

Fangjun Jiang 2011-9-23

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/16572-how-to-amend-an-existing-text-file-in-a-certain-line-and-create-new-ones#answer_22397

When we manually edit a text file, we can go to a particular line, select the whole line, over-write it with some new text and then save the file.

When using fopen() and fprintf(), we can not really do this over-writing selectively, especially when the number of characters in that line is varying. If the text you are overwriting is always at the same position and the length is the same, you can use fseek() to find the position and then over-write the fixed-length of text.

In your case, the only option is to read the whole file, change the content as needed and then write to a different file. After it is done, you can use delete() and movefile() to delete the old file, rename the new file to the old file name.