Can you use the whos command to identify classes

Question

Anthony Koning 2022-10-4

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1817665-can-you-use-the-whos-command-to-identify-classes

评论： Image Analyst 2022-10-5

As the title says, I'm wondering if the whos command (or an equivilent) could be used to get the range and storage requirements on a class in Matlab. For example, the 'double' class ranges from -10^308 to 10^308 amd needs 8 bytes of storage. How would I get these specs for, say, int8? Lookng on the wiki https://www.mathworks.com/help/matlab/matlab_prog/fundamental-matlab-classes.html does not give this information, so can it be obtained with a script? Thanks

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Answer 1

Walter Roberson 2022-10-5

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https://ww2.mathworks.cn/matlabcentral/answers/1817665-can-you-use-the-whos-command-to-identify-classes#answer_1066965

在 MATLAB Online 中打开

numeric_classes = {'int8', 'uint8', 'int16', 'uint16', 'int32', 'uint32', 'int64', 'uint64', 'single', 'double'};
num_classes = length(numeric_classes);
T = table('size', [num_classes, 4], 'VariableNames', {'Class', 'bytes', 'min', 'max'}, ...
    'VariableTypes', ["categorical", "double", "categorical", "categorical"]);
numeric_classes_cats = categorical(numeric_classes);
for K = 1 : num_classes
    class_name = numeric_classes{K};
    class_cat = numeric_classes_cats(K);
    
    sample_variable = zeros(1, 1, class_name);
    class_info = whos('sample_variable');
    class_bytes = class_info.bytes;
    class_bytes_str = string(class_bytes);
    
    if isfloat(sample_variable)
        class_max = realmax(class_name);
        class_min = -class_max;
        class_min_str = categorical(compose("%.16g", class_min));
        class_max_str = categorical(compose("%.16g", class_max));
    else
        class_min = intmin(class_name);
        class_max = intmax(class_name);
        class_min_str = categorical(class_min);
        class_max_str = categorical(class_max);
    end
    T(K, :) = {class_name, class_bytes_str, class_min_str, class_max_str};
end
T
T = 10×4 table
    Class     bytes              min                       max          
    ______    _____    _______________________    ______________________

    int8        1      -128                       127                   
    uint8       1      0                          255                   
    int16       2      -32768                     32767                 
    uint16      2      0                          65535                 
    int32       4      -2147483648                2147483647            
    uint32      4      0                          4294967295            
    int64       8      -9223372036854775808       9223372036854775807   
    uint64      8      0                          18446744073709551615  
    single      4      -3.402823466385289e+38     3.402823466385289e+38 
    double      8      -1.797693134862316e+308    1.797693134862316e+308

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Answer 2

Image Analyst 2022-10-4

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1817665-can-you-use-the-whos-command-to-identify-classes#answer_1066820

在 MATLAB Online 中打开

Try this:

a=uint8([1,2,3]);
dbl = 123.456;
str = 'abc';
s = whos
s = 4×1 struct array with fields:
    name
    size
    bytes
    class
    global
    sparse
    complex
    nesting
    persistent
t = struct2table(s)
t = 4×9 table
       name        size      bytes      class       global    sparse    complex     nesting      persistent
    __________    _______    _____    __________    ______    ______    _______    __________    __________

    {'a'     }    1     3      3      {'uint8' }    false     false      false     1×1 struct      false   
    {'cmdout'}    1    33     66      {'char'  }    false     false      false     1×1 struct      false   
    {'dbl'   }    1     1      8      {'double'}    false     false      false     1×1 struct      false   
    {'str'   }    1     3      6      {'char'  }    false     false      false     1×1 struct      false   

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Image Analyst 2022-10-5

Did you mean a class definition or an instance of a class. Of course a class definition is just a definition of a framework that could contain variables (properties). So you can't get a size of that. However an instance of a class is a variable and you can get the size it uses up with the whos command like I showed.

Image Analyst 2022-10-5

Excel_utils.m

OK I see what you want now, now that I see Walter's answer which you accepted. Of course Walter has the advantage of having the Mind Reading Toolbox, which I don't have yet.

You wanted the range of built-in classes like uint8, double, etc. I thought you wanted classes like classes you made yourself with the classdef command (like my attached Excel utility class), or instances of those classes (actual variables you instantiated as being an instance of the class) or instances of built-in class variables.

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