Why did CD folder; give such a goofy error message when I just forgot ()

It works other places but suddenly I can change directory

K>> apploc

apploc =

'C:\Users\CPSLab\Documents\OdorChoiceDev\'

K>> cd apploc

Error using cd

Unable to change current folder to 'C:\Users\CPSLab\Documents\OdorChoiceDev\apploc' (Name is

nonexistent or not a folder).

Why did it add the variable name to the value of the variable instead of just reminding me I forgot the parentheses

cd (apploc)

Answer 1

[Gavin]

All good answers and I would have retracted the question once I noticed I'd forgotten the ()

Of course cd (apploc) is what I wanted, as I had done before when it worked.

Answer 2

[Matt J]

Because

cd apploc

is equivalent to,

cd('apploc')

This is a general thing in Matlab function-calling syntax. For any function func() taking char vector arguments, the syntax,

func('arg1','arg2','arg3',...)

is equivalent to,

func arg1 arg2 arg3 ...

Answer 3

[Image Analyst]

Since apploc is a variable that contains the actual folder name, you need to use the functional form of cd:

cd(apploc);

If you don't, and omit the parentheses, then it tries to find a folder actually called apploc which does not exist, hence the error.

As a further explanation, if actually did have a folder called MyData and it was a subfolder of your current folder, let's say the current folder was d:\work, then

cd MyData

would change the current folder to d:\work\MyData. It would work in that case. If, unwisely, you also had a variable called MyData and it was a string variable with the value 'My images', then it would still change the current folder to d:\work\MyData since it would use the exact thing you typed (because you did not use parentheses) rather than replacing it with the value of the variable. So it would not change the current folder to 'd:\work\My images'.

But you should not even be using cd anyway. There are few good reasons to use it. You should be constructing full file names using fullfile rather than using cd. See the FAQ:

https://matlab.fandom.com/wiki/FAQ#Where_did_my_file_go?_The_risks_of_using_the_cd_function.

help fullfile

 fullfile - Build full file name from parts
    This MATLAB function builds a full file specification from the specified
    folder and file names.

    Syntax
      f = fullfile(filepart1,...,filepartN)

    Input Arguments
      filepart1,...,filepartN - Folder or file names
        character vectors | string arrays | cell arrays of character vectors

    Output Arguments
      f - full file specification
        character array | string array | cell array of character vectors

    Examples
      openExample('matlab/CreateAFullFileNameExample')
      openExample('matlab/CreateAFullFilePathOnUNIXExample')
      openExample('matlab/CreatePathstoMultipleFilesExample')
      openExample('matlab/CreateaPathtoaFolderExample')

    See also fileparts, filesep, path, pathsep, genpath, split

    Introduced in MATLAB before R2006a
    Documentation for fullfile
       doc fullfile