Sizeof double float int etc

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,

:)

[Yongjian Feng]

Did you try

whos

Answer 1

[Jan]

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...

Answer 2

[Steven Lord]

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

Answer 3

[Fangjun Jiang]

Look at the .bytes returned by whos()

a=false(5);
aInfo=whos('a')
b=zeros(5);
bInfo=whos('b')

Answer 4

[Kevin Holt]

Another option:

function n = sizeof(type) 
  dummy = zeros(1,type);
  n = length(typecast(dummy,'int8'));

Then you can use it for various (non-complex) numeric types, e.g.

sizeof('double') returns 8

whos seems a little more general though.