Why these two path strings are different? (manual string vs. pwd + fullfile)

I am trying to load my file using file path defined in string.

However, although types and values of following variable looks the same, strcmp says they are different:

% WORKSPACE SET TO C:\Users\username\certain_path
pwd = "C:\Users\username\certain_path";
s1 = "C:\Users\username\certain_path\data.mat";
s2 = fullfile(pwd,"data.mat");

strcmp(s1,s2)

ans = logical
   0

Computer never lies. Therefore it seems that I am missing something.

What would be the problem?

[Dongho Kim]

I missed the point that code runner of this site is very likely to be run on Linux systems. Therefore, result on code runner above is valid.

The probloem is that I experienced this issue on my Windows PC. But, since I did not saved any logs for images for it, I can not prove it happened. As I restarted MATLAB, there was no such problem.

One thing I can suspect is that I only used MATLAB as a runner and did all my works by VSCode(With extensions). But, in normal circumstances, this can not be the cause of this problem.

Although even I found myself making a silly question, thank you all for detailed answers.

Answer 1

[Dyuman Joshi]

The file separator character for the OS you have must be backslash, as you get the result of the comparison to be 0.

Let's take a look at the output for the code ran here -

pwd = "C:\Users\username\certain_path";
s1 = "C:\Users\username\certain_path\data.mat"

s1 = "C:\Users\username\certain_path\data.mat"

s2 = fullfile(pwd,"data.mat")

s2 = "C:\Users\username\certain_path/data.mat"

As this code is running on a Unix server, where the file separator character is a backslash, the strings are not equal, as seen above.

If you would check the same on Windows, where the file separator character is a forwardslash, the outcome of strcmp() would be 1.

Reference - fullfile

ver

-----------------------------------------------------------------------------------------------------
MATLAB Version: 23.2.0.2436196 (R2023b) Update 4
MATLAB License Number: 0
Operating System: Linux 5.4.233-0504233-generic #202302250651 SMP Sat Feb 25 12:26:27 UTC 2023 x86_64
Java Version: Java 1.8.0_292-b10 with AdoptOpenJDK OpenJDK 64-Bit Server VM mixed mode
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[Cris LaPierre]

Fullfile determines the proper file separator to use based on your system (\ or /). So your hard-coded separators do not match what fullfile is using.

You can read more here: https://www.mathworks.com/help/matlab/ref/fullfile.html#description

[Dongho Kim]

Thank you for the answer. I missed the point that MATLAB code runner provided runs based on Linux(Obviously.) Therefore, run result on this code must show logical 0 for sure.Thank for pointing out this.

Actually, the reason why I questioned this is because this problem occurred on Windows. But, as I restarted MATLAB, this problem does not occur anymore. Unfortunately, I did not make any screenshots of this.

Still, thank you for the answer so that I will not make this kind of mistake anymore.

[Dyuman Joshi]

"Actually, the reason why I questioned this is because this problem occurred on Windows. But, as I restarted MATLAB, this problem does not occur anymore."

You got the output as 0 when you ran this snippet of code on Windows?

When I run the same code on my PC with Windows, the output is 1. I've attached a screenshot for reference.

[Dongho Kim]

"You got the output as 0 when you ran this snippet of code on Windows?"

Yes this is very embarassing but I have experienced it. No remote, no python bridge or any other use cases other than default MATLAB desktop app.

The image you have provided is indeed an expected behavior.

[Dyuman Joshi]

Nothing embarrassing in that. Just a weird/unexpected behaviour.

"One thing I can suspect is that I only used MATLAB as a runner and did all my works by VSCode(With extensions)."

Maybe you can try this again and see what is the output.

Answer 2

[Walter Roberson]

You will find that on MacOS and Linux (including here on MATLAB Answers) that fullfile uses / separators

[Dongho Kim]

Yes, that's correct. I missed the point that code runner on MATLAB Answers is based on Linux as mentioned on comment above. This is a very silly mistake.

Answer 3

[John D'Errico]

LOOK AT THE STRINGS. They are just strings after all. What is different between them?

pwd = "C:\Users\username\certain_path";
s1 = "C:\Users\username\certain_path\data.mat"

s1 = "C:\Users\username\certain_path\data.mat"

s2 = fullfile(pwd,"data.mat")

s2 = "C:\Users\username\certain_path/data.mat"

s1 == s2

ans = logical
   0

Look at the difference. On your computer system, the path separator is apparently not \, but / (the forward slash). fulfile knows that.

[Dongho Kim]

Since I am very familiar with unix systems, I do know that file separators in Unix systems ans Windows are different.

I tried this code on my Windows system and this problem occurred. It is very unfortunate that I could not take a screenshot but as I restarted matlab, same code showed me 'logical 1'.

I guess something was wrong due to unkown reason, but sadly, I do not have a chance to prove it for now.

I do know this question looks like a silly question. But still, thank you for your answer.