Function to convert relative paths to absolute paths? - matlab

Question

I've spent quite some time to no avail looking for a built-in MATLAB function to convert relative file paths to absolute file paths (portably).
Is there one?
I'm looking for something preferably "built-in" (i.e. available somewhere in the MATLAB distribution, including one of its toolboxes). Even a "package-private" function would be acceptable, as long as I can examine the source code of function. Second best would be a third-party function, as long as it comes with a decent test suite. I am not looking for a function written in response to this question.1
Absent any of the above, even a function to test (portably) whether a path is absolute or not would do (with the same conditions as before: either a "built-in" function or a third-party function with a test suite).
1 The difficulty with implementing such a function is not writing the function itself, but rather writing a sufficiently complete test suite for it (and, of course, making sure that the function passes all the tests!).

Answer 1

fullfile(pwd, relative_path) converts a relative to a absolute path.

Answer 2

You can test if a path is absolute using
javaFileObj = java.io.File(pathToBeTested);
javaFileObj.isAbsolute()
Unlike char(javaFileObj.getCanonicalPath()), which indeed sometimes incorrectly returns a non-existent path relative to C:\Windows\System32, isAbsolute() seems to work properly (tested on Win7, MATLAB 2015b) Therefore the code for constructing the absolute path would look like
function F = rel2abs(F)
if ~java.io.File(F).isAbsolute
F = fullfile(pwd,F);
end
This function has the advantage of being idempotent.

Answer 3

The fullfile(pwd, relative_path) hack works well for me, but if you want something to get you the canonical form, there is no built-in (as of 2015b), but there is a well regarded downloadable script.
http://www.mathworks.com/matlabcentral/fileexchange/28249-getfullpath

Answer 4

See if which fulfills your requirements:
full_path = which(relative_path);

Answer 5

OK, let's resurrect an old thread, if anyone is looking for this.
Here is a method, if you want the absolute path relative to your current working directory (or pwd).
% pwd: 'C:\first\branch'
dir('.\').folder % returns same as pwd, 'C:\first\branch'
dir('..\').folder % returns path one level up from pwd, 'C:\first'
dir('..\parallel_branch').folder % returns the absolute path to "parallel_branch" folder next to pwd, 'C:\first\parallel_branch'

Answer 6

Here's the method that MathWorks themselves uses:
[status, info] = fileattrib(file);
if status
% Return the full path if fileattrib found the file.
fullFilePath = info.Name;
end

Answer 7

For someone landing here with slightly relaxed portability requirements (or a suitable test bench), another idea is to create a folder listing containing only a single file using the built-in dir function, followed by path concatenation using fullfile.
dirListing = dir(relPath);
absPath = fullfile(dirListing(1).folder, dirListing(1).name);
Pros:
Idempotent, i.e. rel2abs(rel2abs(path)) = rel2abs(path)
Simplifies out any /. and /.. in the relative path
Cons:
This only works if the file exists
Tested using Matlab R2020a on Windows