How to change certain lines in a file?
3 vues (au cours des 30 derniers jours)
Hello, I have a text file:
Then, I want to change certain lines of this text file with another condition.
%declaring some variables
fin = fopen('f2.txt','r+'); %opening text file f2.txt in w+ mode
lcounter = 0; %lcounter is a line counter variable
nextline = fgetl (fin); %fgetl() gets nest line of the fin in nextline var
if (lcounter ==1 && a==0) %If both conditions are satisfied, then write **L1 to file
nextline = ['**L1'];
elseif (lcounter ==2 && b==0)
nextline = ['**L2'];
elseif (lcounter ==3 && c==0)
nextline = ['**L3'];
elseif (lcounter ==4 && d==0)
nextline = ['**L4'];
elseif (lcounter ==5 && f==0)
nextline = ['**L5'];
lcounter = lcounter + 1;
Here is the code. What I am trying to do is if both conditions are satisfied, I want to write something to the file. While debugging, I see control goes to the writing statement, but nothing is written to the file. Any idea how to do this?
Ken Atwell le 17 Avr 2015
As Per states, you can't edit an existing file unless the changes are exactly the same size (number of bytes) as the original, which is almost never the case in a text file. I know text editors give the illusion you're only editing individual lines, but in fact the entire file is likely being rewritten on save.
Honestly, I would write a second file line by line. Start with what you have: Read a line, maybe change it, and write the line to a second file that you fopen (with 'w') just before your for loop. You can always replace the original file with the new file when you're done with copyfile or similar -- but don't do that until your code is throughly debugged, or you'll keep clobbering your input data.