problem when write first line to text file

Question

Yu Li 2017-3-6

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/328300-problem-when-write-first-line-to-text-file

评论： Yu Li 2017-3-6

采纳的回答： Jan

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hi: I met some problem when tried to write the first line to text file. below is what the base test file was.

I use the command:

fid = fopen('test.txt','r+')
fprintf(fid,'%s\n','abc');
fclose(fid)

but the result becomes like below:

the first number is deleted.but I could not find why.

could anyone give me some suggestions?

thanks! Li

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KSSV 2017-3-6

I think you cannot write in first line. Better read the content and write to a new text file with first line of your choice.

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Answer 1

Jan 2017-3-6

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https://ww2.mathworks.cn/matlabcentral/answers/328300-problem-when-write-first-line-to-text-file#answer_257472

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You cannot insert characters in a text file. Trying this will overwrite the existing characters. Therefore you have to read the complete file at first, add the string in the memory and write the complete file afterwards:

Str = fileread('test.txt');
fid = fopen('text.txt', 'w');
if fid == -1
  error('Cannot open file for writing.');
end
fprintf(fid,'%s\n','abc');
fprintf(fid, '%s', Str);  % Or faster: fwrite(fid, Str, 'char');
fclose(fid);