MATLAB: I need to access variables of the file from one m file to another

m-filevariable

I am running an M file from another M file. I need to access the variables of first m file from the second.

Best Answer

An example for using input arguments to provide (not "share") variables in a function:

% M-file "fcn1.m"
function fcn1
A = 5;
B = rand(1, 19);
T = fcn2(A, B);
disp(T);
end
% M-file "fcn2.m"

function R = fcn2(A, B)
R = A + 2 * B;
% Remember: this would work also:
% function RRRR = fcn2(AAAA, BBBB)  would work also
% RRRR = AAAA + 2 * BBBB;
end

An alternative is using a "script" instead of a function: The only difference is, that it does not start with "function ..." and has no trailing "end":

% M-file "fcn2.m"
R = A + 2 * B;

In this case, the variables of the caller are shared and modified directly. This works, but as soon as you have many scripts or more than some hundreds lines of code, the confusion will explode. Scripts are much harder to debug, because the effects concerns code in other M-files. Therefore in productive code relying on the clarity of exactly defined inputs and outputs is essential: Use functions to make your life easier.

Related Solutions

MATLAB: How to pass a variable between a m-file and another m-file that runs a gui

M files can contain scripts or functions but variables can only be passed to functions so the m-file must be written as a function [see Scripts vs Functions and Create Function in Files].

For example,

mfile2

function [output] = mfile2(input) 
    % add 1 to the input and pass the result to mfile2.
    y = input + 1; 
    
    % Send y to mfile1 and get the result
    % mfile1 divides y by 2 to z equals (input+1)/2
    z = mfile1(y);
   
end

mfile1

function [output] = mfile1(input)
    % divide the input by two
    output = input/2;
end

All variables needed in a function must either be passed into the function as inputs or defined within the function. If your functions interact with your GUI, pass the handle structure into the function.

MATLAB: How to include many uicontrol object definition defined in one .m file into another . m file

Separate the GUI parts from the calculations. On one hand it is easier to debug or modify the calculationsm on the other hand you can change the GUI later much easier.
If the callbacks of the UI-Controls contain calls to many different functions, you can either create one function file per function and store it in the same folder or the subfolder "\private". Or you can create one wrapper-file to obtain the function handles:

function FcnHandle = myWrapper(FuncName)
FcnHandle = str2func(FuncName);
end
function [a,b] = fcn1(c,d)
...
end
function [a,b,c] = fcn2(d)
...
end
...

Now the many functions files can be stored together in one file and you can get the function handles to define the callbacks like this:

fcn1    = myWrapper('fcn1');
ButtonH = uicontrol('Sytle', 'PushButton', 'Callback', {@myPushCB, fcn1});
...
function myPushCB(ObjectH, EventData, FcnHandle)
c = rand;
d = rand;
[a,b] = FcnHandle(c, d);

Hmmm. This works, but I'm not convinced, that this is smart: During debugging it is hard to get the inforamtion, which function is called in the callback. Another method might be nicer:

function [a,b,c,d] = myWrapper2(FuncName, varargin)
switch FuncName
  case 'fcn1'
    [a,b] = fcn1(varargin{1:2});
  case 'fcn2'
    [a,b,c] = fcn1(varargin{1});
  otherwise
     error('Unknown function: %s', FuncName):
end
...
FcnHandle = str2func(FuncName);
end
function [a,b] = fcn1(c,d)
...
end
function [a,b,c] = fcn2(d)
...
end

Now the bunch of functions can be called through one wrapper function:

function myPushCB(ObjectH, EventData, FcnHandle)
c = rand;
d = rand;
[a,b] = myWrapper2('fcn1', c, d);

This allows to see directly, which function is called.

This is only useful, if there is a need to keep all functions in one file. It would be easier to create one file per function, because then the wrapping is not needed.

Best Answer

Related Solutions

MATLAB: How to pass a variable between a m-file and another m-file that runs a gui

MATLAB: How to include many uicontrol object definition defined in one .m file into another . m file

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