problem when write first line to text file

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Yu Li
Yu Li 2017-3-6
评论： Yu Li 2017-3-6
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
  1 个评论
KSSV
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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采纳的回答

Jan
Jan 2017-3-6
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);

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