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Sizeof double float int etc

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R. Can
R. Can on 30 Jun 2021
Answered: Steven Lord on 30 Jun 2021
Hello there,
I need to know how to find an equivallent function in Matlab to the sizeof function in c++.
For example, in c++ if I write sizeof(double) I would get the amount of memory needed to store a double.
I need something very similar with a matrix now. I will be storing bigger and bigger matrix and I need to find their size in the memory.
Could someone of you please help me?
all best,
:)

Accepted Answer

Jan
Jan on 30 Jun 2021
Edited: Jan on 30 Jun 2021
Version 1:
w = whos('z');
nbytes = w.bytes;
Version 2:
function S = sizeof(X)
switch class(X)
case {'uint64', 'int64', 'double'}
m = 8;
case {'uint32', 'int32', 'single'}
m = 4;
case {'uint16', 'int16', 'char'}
m = 2;
case {'uint8', 'int8', 'logical'}
m = 1;
otherwise
error('Jan:sizeof:Type', 'Type not handles: %s', class(X));
end
S = m * numel(X);
end
A search inthe forum leads me to: https://www.mathworks.com/matlabcentral/answers/391214-does-matlab-have-a-function-which-is-similar-with-sizeof-in-c#answer_312420 . Obviously I have some standard programming styles...

More Answers (2)

Fangjun Jiang
Fangjun Jiang on 30 Jun 2021
Look at the .bytes returned by whos()
a=false(5);
aInfo=whos('a')
b=zeros(5);
bInfo=whos('b')

Steven Lord
Steven Lord on 30 Jun 2021
I need something very similar with a matrix now. I will be storing bigger and bigger matrix and I need to find their size in the memory.
Why? If you're trying to create an array to be filled in, just call a function like ones or zeros and tell it the size of the array you want to create (in terms of number of elements) and optionally the type. There's no need for you to know (or care) how much memory each element takes up in order to build the array.
A = ones(2, 3, 'int16')
A = 2×3
1 1 1 1 1 1
B = zeros(5) % 5-by-5 double array
B = 5×5
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

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