"Error using save Must be a string scalar or character vector." - but it is a string!

Question

EQ 2019-4-7

评论： Walter Roberson 2021-8-4

I'm getting the error when I run the following line:

save(['data/test',num2str(n),'.mat'],U,U_old,dt);

where n is my loop index. This is bizarre. For the record, when I stop at the breakpoint, typing this at the command line works:

save data/test1.mat U U_old dt

But I need to be able to change the filename within the loop, hence why I'm doing it the first way. When I type this at the command line:

['data/test',num2str(n),'.mat']

I get the expected 'data/test1.mat' result. The variable U is an 889x4 matrix, U_old is the same size, and dt is a single float. Even typing

save('data/test1.mat',U,U_old,dt);

at the command line when I stop gives me this error. What gives?

Answer 1

A. Sawas 2019-4-7

编辑：A. Sawas 2019-4-7

You need to enclose the variable names with qoutations like this:

save(['data/test',num2str(n),'.mat'],'U','U_old','dt');

Jeet Shetty 2021-8-4

what is n in your particular code, i have gotten the same error

Walter Roberson 2021-8-4

At the time the user got the error, n was 1.

Answer 2

Walter Roberson 2019-4-7

save( sprintf('data/test%d.mat', n), 'U', 'U_old', 'dt');

The quotes around the U and so on are the important part for your problem; the sprintf is just a cleaner way of creating the file name.

Shuting Li 2021-2-3

And where can I add filepath? I want to save file in other filepath? Thank you very much

Walter Roberson 2021-2-3

filename = fullfile(filepath, sprintf('test%d.mat', n));
save(filename, 'U', 'U_old', 'dt');