Acquiring variable names to be used in fieldnames

Hi, I have a structure (abcSTRUCTUREdef) in my work space containing a list of variables. I use the following function to get all the varibles from the structure as a workspace variables.

%%%%%%%%%%Original Code %%%%%%%%%%%

fields = fieldnames( abcSTRUCTUREdef, '-full'); % Find out how many there are - for our loop.

numberOfFields = length(fields);
for f = 1 : numberOfFields;

thisField = fields{f};

commandLine = sprintf('%s = abcFIELDdef.%s', thisField, thisField);

eval(commandLine);

end

% Release temporary variables.

clear('f', 'thisField', 'numberOfFields');

clear('fields', 'commandLine');

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

However I would like to automate the whole process by just using it as a script where it acquires the structure name from the work space such that, (for example)

varNames = who;
structName = varNames{1,1};

fields = fieldnames( structName, '-full'); % Find out how many there are - for our loop.

commandLine = sprintf('%s =' structName '.%s', thisField, thisField);

However everytime I attempt this, I get an error saying that "Undefined function 'fieldnames' for input arguments of type 'char'."

This is the end of a long script that pulls data out of folders. I would really appreciate your help.

Many thanks.

[Stephen23]

It is not clear what you are trying to achieve, but using eval is highly unlikely to be an efficient or neat way of doing it. Using eval is usually slow, buggy, and almost impossible to debug (as you are finding out now). Not only that it removes lots of very useful tools and code checking that MATLAB has to help you write good code. Read this (and all of the links) to know why eval is a poor approach for most tasks:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

https://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html

Instead of writing buggy, slow code like this, why not explain to us what you are actually trying to achieve, and we can show you a better way of coding it.

[Abhi Ove]

Hi I have multiple structure in my workspace. I would like to:

1) workSpaceVarName = who; % to acquire a list of variables in my workspace and then specifically use the field function

2) NAMES = fieldnames( workSpaceVarName{1,1} ,'-full') % to get all the details of each structure.

I hope I make sense, but please do let me know if I do not.

Many thanks.

[Stephen23]

@Abhi Ove: thank you for your explanation. What you are trying to do is not a good way to write code. Please read my comment and its links to know why. The links also explain better ways to write code.

Answer 1

[Walter Roberson]

"NAMES = fieldnames(S) returns a cell array of character vectors containing the names of the fields in structure S.

NAMES = fieldnames(Obj,'-full') returns a cell array of character vectors containing the name, type, attributes, and inheritance of the properties of Obj. Only supported for COM and Java objects."

You are trying to apply fieldnames to a cell array of strings that are variable names. There is no direct MATLAB operation to get the fieldnames of a variable whose name you know.

[Walter Roberson]

There is no direct way to ask for the fieldnames of a variable whose name is known. You would need

 NAMES = fieldnames( eval(workSpaceVarName{1,1}) );