CODEWITHSUNDEEP
matlab
user288609
user288609

Reputation: 13015

regarding using "clear all;" in functions

I have several MATLAB scripts, e.g., fun1, fun2,...etc There can have dependency relationships among them. For instance, fun1 can call fun2 and fun2 can call fun3.

In order to remove unnecessary variables, should I put “clear all;” at the head of every functions.

function x1 = fun1(input1)
clear all;
...

Will this cause any potential issue, such as removing useful variables?

Upvotes: 0

Views: 3884

Answers (4)

Sam Roberts
Sam Roberts

Reputation: 24127

Several answers so far have explained that using clear all at the start of a function is not a helpful thing to do, as it will clear the input variables.

I'd just add that clear all is often misused even in scripts. clear all does more than just clear all variables from the current workspace; it also removes all functions, MEX files and any imported Java classes from memory (so many things will subsequently run more slowly if they need to be reloaded), reinitializes persistent variables, and removes any debug points.

If all you want to do is to clear variables, just use clear (or clearvars or clear variables).

Upvotes: 2

Pursuit
Pursuit

Reputation: 12345

No, no no, 1000 times no.

The function declaration will give you a clean workspace. When a function exits, the workspace (and all variables) will be cleaned up, except for globals and persistents.

Even in scripts, I discourage the use of indiscriminate clear all statements. If you are in a position to need that feature, the function keyword at the beginning of a file serves to clean up your workspace, without destroying anything else that you may happen to be working on.

Upvotes: 1

Dang Khoa
Dang Khoa

Reputation: 5823

Assuming fun1, etc, are typical functions (e.g., not nested functions or anything), each function gets its own workspace. The only variables you'll have in this new function workspace are the input variables - so doing a clear all as the first call in the function will clear the input variables. Your function wouldn't be able to operate on the inputs.

If you have a nested function, that nested function will be in the same workspace as the parent function - so a clear all would obliterate the parents' variables, as well.

In general, only scripts should start out with clear all, if you want your base workspace clean before running the script.

Upvotes: 1

John
John

Reputation: 5905

All clear all will do in that context, is to remove your input variables. When you are within a function, the only variables that function sees are the variables passed into the function. So, you will find that to be not a particularly helpful pattern.

Upvotes: 5

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