Global variable keeps initialising again and again when I want it to only initialise once.

I have a GUI in MATLAB with a pushbutton called plot. When I click on plot as expected a figure appears. But my doubt is this. I want a global variable which is initialized to 1, the first time I run the GUI and then increment by 1 every time I press plot. I tried to do this but my global variables keeps initializing back to 1 every time when I press plot. I dont want that. I want that global variable to be initialized only one when I run the GUI and must increment every time I press plot. How can I do this. Kindly help me. Thanking You.

[Rik]

Avoid using globals. You don't need it. Use the guidata struct instead (or even setpref and getpref)

[Stephen23]

Global variable keeps initialising again and again ...
^^^^^^^^^^^^^^^ this is the problem here.

Answer 1

[Jan]

Avoid globals. As you can see already, they confuse programmers and impede the debugging. Do not use globals. For tiny codes globals can look like they solve a problem efficiently, but as soon as the codes grow or as you use different tools (maybe written by different programmers), the confusion is perfect. So implement your solution without globals in general. Globals are evil.

Do you press the same button to create the new figures? Then use e.g. the UserData of this button:

function ButtonCallback(objectH, EventData, handles)
UD = get(objectH, 'UserData');
if isempty(UD)
    UD = 0;
end
UD = UD + 1;
set(objectH, 'UserData', UD);

disp(UD)
end

Now UD is increased by one each time the button is pressed.

You can store the number in the UserData of the figure also, or inside the handles struct - then update this struct by guidata, such that the update is stored in the ApplicationData of the figure.

If you really do not see a way to avoid globals or love them for unknown reasons, use them correctly:

• Create a unique name, not a single character
• Add the global statement in all functions, which use this variable
• Care for a well defined location, where this global variable is initialized

Your description sounds, like you call something like this repeatedly by accident:

global X
X = 0

To help you to find the problem, we need to see the code.

[Govind Sankar Madhavan Pillai Ramachandran Nair]

global x
x = 0

its like this. But this is in the first function of the GUI program. I thought that function will only be called only one time. Under plot there is only

global x 
x=x+1

I dont have any love for global variables. I try to avoid global variables in other programming languages. I am only starting in MATLAB GUI. That is why I tried to use global variable. I am extremely satisfied with your solution. I am going to use your solution.

function ButtonCallback(objectH, EventData, handles)
UD = get(objectH, 'UserData');
if isempty(UD)
    UD = 0;
end
UD = UD + 1;
set(objectH, 'UserData', UD);
disp(UD)
end

But I want to use this UD in another function. How do I do that and also I need to learn about this method. So what should I search in google to learn about this method, so that I can use this in the future.

[Rik]

Read the documentation if you want to learn about this function. The Matlab doc is actually one of the better ones for programming languages.

[Stephen23]

https://www.mathworks.com/help/matlab/creating_guis/share-data-among-callbacks.html

https://www.mathworks.com/help/matlab/ref/set.html

https://www.mathworks.com/help/matlab/ref/get.html