How to use fprintf in Matlab R2016a

Question

Ali 2016-6-9

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链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/288840-how-to-use-fprintf-in-matlab-r2016a

编辑： Stephen23 2016-6-9

采纳的回答： Stephen23

在 MATLAB Online 中打开

I am working with Matlab R2016a, and I get error for the follwing code which is form mathworks's website.

The thing is whenever I use fprintf, I get the same error.

Thanks a lot for the help.

 x = 0:.1:1;
 A = [x; exp(x)];
 fileID = fopen('exp.txt','w');
 fprintf(fileID,'%6s %12s\n','x','exp(x)');
 fprintf(fileID,'%6.2f %12.8f\n',A);
 fclose(fileID);

Error:

Error using fprintf

Invalid file identifier. Use fopen to generate a valid file identifier.

Error in Untitled (line 5)

fprintf(fileID,'%6s %12s\n','x','exp(x)');

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Answer 1

Stephen23 2016-6-9

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/288840-how-to-use-fprintf-in-matlab-r2016a#answer_224975

编辑：Stephen23 2016-6-9

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The problem really has nothing to do with fprintf, it is actually because fopen cannot open the file that you are telling it to. This typically happens to beginners when they do one of these:

have spelling mistake in the filename.
try to open a file that does not exist.
don't put the required path information, even though the file is located somewhere other than the current directory.
try to read or write to a location where they do not have permission.

You can find what fopen says about its troubles by having a look at its second output:

[fileID,msg] = fopen('exp.txt','w');

What is the information in msg ? What does it say ?

For every case (except the last) the solution is always the same: provide fopen with the correct path information. The last case has nothing to do with MATLAB: if a user does not have permission for a folder then this is not MATLAB's problem.

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Ali 2016-6-9

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Many thanks for the cooperation.

 x = 0:.1:1;
 A = [x; exp(x)];
 P = pwd
 [fileID, msg] = fopen('exp.txt', 'w')
 fprintf(fileID,'%6s %12s\n','x','exp(x)');
 fprintf(fileID,'%6.2f %12.8f\n',A);
 fclose(fileID);

I got the following:

 P =
 C:\Program Files\MATLAB\R2016a\bin
 fileID =
    -1
 msg =
 Permission denied
 Error using fprintf
 Invalid file identifier. Use fopen to generate a valid file identifier.
 Error in Untitled (line 5)
 fprintf(fileID,'%6s %12s\n','x','exp(x)');

Stephen23 2016-6-9

编辑：Stephen23 2016-6-9

在 MATLAB Online 中打开

So, finally lets have a look a the information you have given us:

 P =
 C:\Program Files\MATLAB\R2016a\bin
 msg =
 Permission denied

The path is somwhere in the MATLAB installation directory. Why are you trying to save there? Quite rightly, Windows is stopping you (as the message clearly says) from saving or altering files inside the program directory. This has nothing to do with MATLAB, and is caused by that fact that you are trying to save a file somewhere where you are not (normally) allowed to. Your OS is stopping you from damaging your installed programs!

The solution is to save your file somewhere where you do have permission. Normally this would be in the users' directories. You might also need to change the MATLAB current directory, as it should definitely not be inside the program files directory.

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