how Modify text file ,Write new values

Hi: I have a text file that is an input file to a simulator program and I want to change some input variables and transfer them back to the simulator program (for example afw in row 48 of column 8), when I do this May_made changes in MATLAB but the text file in the main folder still does not change, please help

filename=fullfile('D:\','app','try1','TRY1B','w2_con.npt ');
 fid = fopen(filename,'r');
 format = repmat('%s',[1,10]);
A = textscan(fid,format);
A=[A{:}];
fclose(fid);
% Change cell A
 A{48,8}=sprintf('%d',6);

Answer 1

[Walter Roberson]

%do not overwrite the old file; we are counting on the old field being 15.0000

filename = fullfile('D:\','app','try1','TRY1B','w2_con.npt ');
newfile = fullfile('D:\','app','try1','TRY1B','new_w2_con.npt ');
S = regexp( fileread(filename), '\n', 'split');

newval = 6;
S{48} = regexprep(S{48}, '15\.0000', sprintf('%.4f', newval), 'once');

S = strjoin(S, '\n');

[fid, msg] = fopen(newfile, 'w');   %not 'wt'
if fid < 0
    error('Failed to open file "%s" for writing because "%s"', newfile, msg);
end
fwrite(fid, S);
fclose(fid);

If you cannot count on the field to replace being a specific value, then you may have to replace by position, which can be a bit tricky as it looks like you might possibly be using fixed width fields (or possibly they are tab separated.)

Your existing code to read the fields is not going to do well on lines such as

WB 1          ET     OFF     OFF      ON     OFF 15.0000 2.00000 2.00000 10.0000

as the character fields are permitted to have embedded blanks which you are reading in as separate fields.