How can I access the value of a string variable? I need to construct a file path from a string variable, but keep getting the variable name and not the string.

I want to construct a file path, "f" that I will use many times in a Matlab m file. From advice in an answer to someone else's question, I am using the "fullfile" function. However, I am having what seems like a silly problem. Please see the example below.

I want to put "directory1" in the file path to get:

/Users/me/ch4/directory1/directory2/results/file_1.dat

However, when I do:

directory_name = "directory1";
f = fullfile('/Users/me/ch4', directory_name, 'directory2/results/file_1.dat')

I get:

Error using matlab.io.ImportOptions/readtable (line 503)
Unable to find or open '/Users/me/ch4/directory_name/directory2/results/file_1.dat'. Check the path and filename or file permissions

How can I substitute the contents of the variable and not the variable name in the file path? Thank you for any advice.

Answer 1

[Sulaymon Eshkabilov]

It can be done these ways.

Way1:

directory_name = "directory1";
f = fullfile(['/Users/me/ch4/', directory_name, '/directory2/results/file_1.dat']);

Or

Way 2:

directory_name = "directory1";
f = strcat(['/Users/me/ch4/', directory_name, '/directory2/results/file_1.dat']);

[Srh Fwl]

@Sulaymon Eshkabilov, thank you very much. I'm not sure what I'm doing wrong. When I try your suggestions, I do get the value of directory_name, but I don't get a file path.

>> f =

1×3 string array

"/Users/me/ch4/" "directory1" "/directory2/results/file_1.dat'"

[Srh Fwl]

@Sulaymon Eshkabilov, I figured it out. I put the square brackets only around "directory_name." If you want to modify your answer, I would be happy to accept it. Thank you for your help.

I.e.,

f = strcat('/Users/me/ch4/', [directory_name], '/directory2/results/file_1.dat');

[Sulaymon Eshkabilov]

If you want to get the file directory, then use one of these:

Note: " " vs. ' '

directory_name = 'directory1';
f = fullfile(['/Users/me/ch4/', directory_name, '/directory2/results/file_1.dat']);

Or

directory_name = 'directory1';
f = strcat(['/Users/me/ch4/', directory_name, '/directory2/results/file_1.dat']);

[Stephen23]

"I figured it out. I put the square brackets only around "directory_name.""

No, you do not need superfluous square brackets only around DIRECTORY_NAME.

"If you want to modify your answer, I would be happy to accept it."

Ugh. Note that Sulaymon Eshkabilov's code concatenates everything together using square brackets and then calls FULLFILE and STRCAT... which then do absolutely nothing. Do not follow their advice of filling your code with unused functions that do nothing, without understanding what the code does.

Do NOT use this code.

Answer 2

[Stephen23]

It works perfectly, exactly as you showed in your question:

directory_name = "directory1";
f = fullfile('/Users/me/ch4', directory_name, 'directory2/results/file_1.dat')

f = "/Users/me/ch4/directory1/directory2/results/file_1.dat"

The problem is that the code you actually used is something like this:

%                             v              v  ooops
f = fullfile('/Users/me/ch4', 'directory_name', 'directory2/results/file_1.dat')

f = '/Users/me/ch4/directory_name/directory2/results/file_1.dat'

Do not use square brackets anywhere. If you do, you are making a big mistake (just like Sulaymon Eshkabilov did). Your original approach using FULLFILE is the best approach, the problem is not solved by square brackets.

[Srh Fwl]

@Stephen23, thank you for that information. Sorry, I still don't understand what the problem is with the square-brackets solution. It works when I use square brackets around the variable name. I apologize for being dense. It has been a long day so maybe I need to sleep on it and take a second look tomorrow! To be clear, I specifically checked I had not used quotes around the variable name.

[Stephen23]

"Sorry, I still don't understand what the problem is with the square-brackets solution."

It is not a solution to your problem. Square brackets are a concatenation operator: when you place square brackets around one array like this:

f = strcat('/Users/me/ch4/', [directory_name], '/directory2/results/file_1.dat');
%                            ^              ^ these do nothing

then you are concatenting that one array with... nothing else. This is the definition of pointless.

This is also a good example of https://en.wikipedia.org/wiki/Shotgun_debugging

It is clear that the actual problem lies (or lay) somewhere else. We could help you to debug this properly if you showed us the actual code you used (not edited, simplified, modified, changed, etc for this forum). Verbatim code please.

[Srh Fwl]

The only thing I have changed is the directory names. Everything else is verbatim. Anyway, it works now thanks to Sulaymon. Thank you.