how to open *.txt files with variable names

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zahra matlab 2014-10-13

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编辑： Stephen23 2019-3-4

hi I have a function '[dl]=funcall(x,y)' and in it I want to create *.text file with variable names and write out put vectors 'dl'. such as this

    function [dl]=funcdl(x,y)
    .........
    fid=fopen('DL.txt', 'wt');
    fprintf(fid, '%f\n',dl);
    fprintf(fid, '\n');
    fclose(fid);
    ......

but every time by calling function it creates the same name 'DL.txt' and overwrites out put!!! any one can help me???

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Stephen23 2014-10-13

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编辑：Stephen23 2014-10-13

If you are talking about creating files with sequential filenames, these might be helpful to read:

http://www.mathworks.com/matlabcentral/answers/57446-faq-how-can-i-process-a-sequence-of-files

http://matlab.wikia.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

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Stephen23 2014-10-13

编辑：Stephen23 2014-10-13

在 MATLAB Online 中打开

Try this, for example:

for k=1:3
    str = sprintf('temp%d.txt',k);
    fid = fopen(str,'wt');
    ...
    ... write data to your file here (fprintf, or whatever...)
    ...
    fclose(fid);
end

EDIT: uses sprintf, based on the comments of Image Analyst and Robert Cumming.

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Gaurav Shukla 2014-10-13

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在 MATLAB Online 中打开

Consider an array

VarName = [A,B,C];

for i=1:3
str = strcat('fopen(''',VarName(i),'.txt','wt');
eval(str);
end

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Andrew Reibold 2014-10-13

编辑：Andrew Reibold 2014-10-13

I was reading that list of coding practices that make at least Doug cry, and he didn't really explain why eval was bad. He was just kind of like 'There is already another way to do it, and that way is the 'right' way'. Yes sure, there is another way to do it. A way that is less clear to noobies and takes more time for them to use.

Eval is frankly much easier to understand and hasn't caused any issues in my experience.. . That is why it is so popular. I don't get why people hate on it so much.

Who cares if you open file names with eval if it works and its easy and its fast. Isn't that what we want? Fast, easy, effective? I open file names with eval all the time and it works like a charm. And the amount it takes to read a file is much larger than the time it takes to run an eval function so much so that the time it takes to run eval is negligible.

Also, complaining his code is ineffective for using 'i' is pretty trivial. Obviously its just an example... and he can use ii, cat, whale, or bad_coding_practice_here if he wanted. If he is using imaginary numbers at all he probably knows better or will soon find out there is an issue.

Stephen23 2014-10-13

编辑：Stephen23 2019-3-4

在 MATLAB Online 中打开

The code that Gaurav Shukla wrote includes this line:

str = strcat('fopen(''',VarName(i),'.txt','wt');

However it is wrong code: that string, when evaluated, produces an error, as it is also missing the closing bracket. Did anyone spot this? Was it easy to see, or is it obfuscated in the middle of the ton of brackets and quotation marks? Perhaps they also noticed that this string has the wrong number of quotation marks? More likely they lost track trying to figure out how many quotation marks it needs, just like its author did.

Two major syntax errors in one line of code, due to the obfuscation allowed by using eval. If the function had been called directly, then MATLAB's code editor would simply highlight these coding errors, but it can't do that here because the code is obfuscated in a string: unfortunately the code was NOT actually "easier to immediately understand and see the intent of"! What a shame that its author could not use any of MATLAB's automatic code hinting, could not rely on the syntax checking in the editor, and could not press the F1 key to bring up the help for the function that they were currently typing...

For those who are curious, the error occurs only when the eval statement is called:

>> eval(str);
Error: A MATLAB string constant is not terminated properly.

There is no indication where, or on which line, or in what function this error occurs, or how I could try to find it and fix it... how does this support the argument that "for this one off example, eval is a fast, simple, effective, clear solution" when it doesn't work and it isn't clear how to fix it?

Good coding doesn't depend only on "plans for future use", but making the best use of all of MATLAB's tools and help, including optimizing, debugging, mlint, etc.

There is no better day than today to start learning good coding practices.

Stephen23 2015-1-4

编辑：Stephen23 2015-1-4

How about this example (from one of your own questions):

http://www.mathworks.com/matlabcentral/answers/157722-title-string1_string2-stop-automatic-subscripts

In a comment to one of the answers to that question you write "Its just that the code I inherited is just an absolute catastrophe when it comes to formatting and practice".

This seems to contradict your earlier comment on this thread: "I'm all for good coding practice, but at the same time when you need a fast, effect, simple, easy to understand solution for a quick job, sometimes being an elitist about your code is more of a hinderance and bottleneck then anything else".

And yet it seems that someone else's "fast, effect[ive], simple" solution became your "absolute catastrophe" problem to solve, which really did cause you a "hinderance and bottleneck" : not because it was well written code, but because it was poorly written code and because this is usually what poorly written and obfuscated code does.

MATLAB's inbuilt tools help to avoid basic syntax mistakes, which goes part of the way to writing good code. So, dear reader, why not use them?

Stephen23 2015-1-4

For new readers, read all of these comments and

Do NOT use this code

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