Difference between clear var and clear var*

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Rowan Lawrence 2019-8-30

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https://ww2.mathworks.cn/matlabcentral/answers/478339-difference-between-clear-var-and-clear-var

评论： Rowan Lawrence 2019-8-31

Hi all,

This will probably be a very straightforward question but I can't get to the bottom of it. I just started reading Mike Cohen's book 'MATLAB for Brain and Cognitive Scientists' this afternoon. He suggests checking the difference between 'clear a' and clear a*' in one of the preliminary chapters. They don't appear to do anything different. I have read the MATLAB documentation for 'clear' again (not to much to chew on), and I can't see anything.

Given what little I know about pointers from C++, I initially imagined that clear a* would remove the value stored in a from the workspace, but that the memory allocated to it would remain (just empty); and that clear a would remove variable a from the workspace entirely. I then checked both with 'whos' and both commands simply remove the variable and its value.

I downloaded a set of tip scripts from Mike's website for the book. The tip for that part of the chapter is simply:

%% 6
clear a
clear a*

In a last-ditch effort, I Googled it in a few different ways, but turned up nothing.

There are a thousand more interesting issues and questions I could ask, but this is just driving me up the wall because I can't find the answer, even though I know it will be simple. Does anybody know what exactly he is trying to get at with this?

Cheers!

Rowan.

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Answer 1

Steven Lord 2019-8-31

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https://ww2.mathworks.cn/matlabcentral/answers/478339-difference-between-clear-var-and-clear-var#answer_389856

在 MATLAB Online 中打开

Let's start with a blank workspace.

>> clear all

Create three variables and check that they all exist in the workspace.

>> a = 1;
>> ab = 2;
>> abc = 3;
>> whos
  Name      Size            Bytes  Class     Attributes
  a         1x1                 8  double              
  ab        1x1                 8  double              
  abc       1x1                 8  double              

Run the first command. What's in the workspace now?

>> clear a
>> whos
  Name      Size            Bytes  Class     Attributes
  ab        1x1                 8  double              
  abc       1x1                 8  double              

Run the second command. What's in the workspace now?

>> clear a*
>> whos
>> 

If you're not certain exactly what a particular command does, I recommend checking its help text and/or its documentation. In this case, the help text describes how "clear a*" is interpreted.

>> help clear

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Rowan Lawrence 2019-8-31

Ah, so the * is acting as a wildcard for the variable names. I had assumed it was related to the memory of the variable, which is why I was confused (probably why I couldn't find anything in the docs!)

Thankyou for the answer Steven; sanity returned.

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