Using fprintf to write to multiple files simultaneously
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I want to write the same text to the screen and in to a file. So I have to double the code:
fprintf('this is some text with numbers: %d, %d', x,y);
fprintf(fid, 'this is some text with numbers: %d, %d', x,y);
Alternatively I can introduce a text string to avoid double code:
str = sprintf('this is some text with numbers: %d, %d', x,y);
fprintf(str);
fprintf(fid, str);
But obviously it does not work to use fprintf to write to mutliple files simultaneously? Would be nice if possible.
fprintf([1 fid],'this is some text with numbers: %d, %d', x,y);
采纳的回答
Ameer Hamza
2020-4-9
编辑：Ameer Hamza
2020-4-9
As far as I know, this feature is not natively supported by MATLAB. But if it is really important for your application, then you can try the following two methods.
First, create a custom function which takes an array of FIDs and call fprintf one by one on each of them. Save the following function in a file printf.m in MATLAB's path.
function printf(fid, varargin)
for f = fid(:)'
fprintf(f, varargin{:});
end
end
Call this function
f = fopen('test.txt', 'w+');
printf([1 f 1 1 f], 'hello world\n');
fclose(f);
Second, overload the fprintf function. Create a folder name @double in your MATLAB's path and save the following function in file fprintf.m
function y = fprintf(fid, varargin)
y = zeros(size(fid));
for i = 1:numel(fid)
y(i) = builtin('fprintf', fid(i), varargin{:});
end
end
[Important note:] The definition of overloaded function is updated; the first code can break the compatibility in some cases.
Call this function
f = fopen('test.txt', 'w+');
fprintf([1 f 1 1 f], 'hello world\n');
fclose(f);
Note that this overloading will not break compatibility, other programs calling fprintf() will still work normally.
As a side note, these functions can also be written as one-liners without for-loop:
printf.m:
function printf(fid, varargin)
arrayfun(@(f) fprintf(f, varargin{:}), fid);
end
fprintf.m
function y = fprintf(fid, varargin)
y = cell2mat( arrayfun(@(f) {builtin('fprintf', f, varargin{:})}, fid) );
end
更多回答（1 个）
Walter Roberson
2020-4-9
3 个投票
You are correct, any one fprintf() can only write to one place at a time.
You should have a look at diary
3 个评论
Lionel Trebuchon
2022-7-26
Hello Walter!
Do you know of a functionality (even hidden/undocumented) to write diaries/logs to two locations simultaneously? The code of diary is hidden to us.
The context is a slightly unstable system, and we want to enhance our chances to access the logs one way or the other.
We would rather prefer not to brute-force, i.e. copy the full logs, as they can get quite long.
Thanks!
Best, Lionel
Steven Lord
2022-7-26
You could try launching MATLAB with the -logfile option and also call diary in that session. The two files won't be exactly the same but they may be close enough for your purposes.
But for problems like the original question and for this, if I wanted to log information to multiple places I'd write a function that I could call with a vector of file identifiers (and potentially some "dummy" identifier if I wanted to write to the screen as well) that would write to all those locations.
function logToFilesAndScreen(fid, varargin)
% logToFilesAndScreen Write text to one or more files and to the screen
%
% logToFilesAndScreen(fid, varargin) writes the information stored in
% varargin (which must contain valid inputs to the fprintf function when
% passed to it as a comma-separated list) to the screen and to all the
% files whose file IDs (as opened using fopen) are passed in as the fid
% input.
% Print to screen
fprintf(varargin{:})
% Print to file(s)
for whichfile = 1:numel(fid)
fprintf(fid(whichfile), varargin{:})
end
end
Walter Roberson
2022-7-26
编辑：Walter Roberson
2022-7-26
Note: identifier 1 always writes to the screen (well, unless MATLAB has been run in non-interactive mode.)
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