Number of Files for a Program Script

I have a script where I have called a function. I have defined this function in a separate file to the main script - does that make sense ? The code for the main script works perfectly fine so the function must be defined and used correctly. However, when I run the script containing the function, it doesn't work due to errors. This is expected right ?

Also, is it best practice to have a separate script as I have done for my function ? (separate to the script for the main program where the function is called).

Answer 1

[Walter Roberson]

Functions in separate files are potentially reusable, which is a good thing.

Functions in the same file are often convenient.

Functions in the same file can offer some guarantees about where exactly the function will be resolved from. For example suppose your script calls MyFun in the same directory as your script but someone is in a different current directory when they run the script: can you be sure that the MyFun in the same directory is the MyFun that will be used? (Answer: No, not unless you used private/ subdirectory). So putting into the same file gives a level of certainty.

[Kimi Raikonnen]

Thanks for the reply. If I put them in the same file, where would I define the function. I have to define it before I call it right ? Also, then I think I would need to change the name of either the function or script file

[Steven Lord]

If I put them in the same file, where would I define the function.

If you have a local function in a function file it needs to be defined after the main function. If that local function occurs in a script file it needs to be defined after any of the code that is part of the script portion of the file. You can't write part of your script, define a function (except for anonymous functions), then continue on with the script. MATLAB will error if you try to do that.

I have to define it before I call it right ?

If by "before" you mean on a line whose line number is smaller than the line number of the line where you call it, no. You can have a call to a function on line 50 where the definition of that function starts on line 100, for example.

Also, then I think I would need to change the name of either the function or script file

Any function defined in a script file cannot have the same name as the script file, correct.

[Kimi Raikonnen]

Thanks for the reply. So for me I think it’s easier to have the function in a separate file as the main script runs perfectly and calls the function correctly.

Just to clarify, it is normal and expected that the function on its own in its own separate file, when I run it, that it doesn’t work and I get N error ?

[Walter Roberson]

If you run a function by itself, and it is a function that requries inputs, and you do not provide the inputs, then you would (typically) receive an error message.

The issue is not with it being in a separate file: the issue is with correct inputs being required. Which is a problem whether it is in the same file or a different file.

Note: there is one sort-of- exception:

If you have a function that defines a function inside of it, like

outer()

outer here
inner here

function outer
   disp('outer here')
   inner();
    function inner
        disp('inner here')
    end
end

then variables that are defined in the outer function before calling the inner function can be "shared" with the inner function. In that particular case, moving the inner function to its own file can result in it no longer having access to the variables.

Oh, and of course if you move a function to its own file, then it can no longer access other functions defined in the same file.

[Kimi Raikonnen]

Okay thanks for your help. I now defined the function in the script where I called it in the same file.

Question: where would it be best to define the function?

I defined it at the end / bottom of my program after I called it. Is this okay ? Or would you recommend defining it elsewhere in the program ?