Does Matlab have a function which is similar with sizeof in C?

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Linan Xu
Linan Xu 2018-3-28
编辑： Jan 2021-4-13
For example, if I type sizeof('double'), the function can give me 8. Let me know whether Matlab has a function working similarly with sizeof in C language.
  2 个评论
Steven Lord
Steven Lord 2018-3-28
How would you use such a function if it existed? You don't need to allocate memory yourself like you do in C, instead you should use functions like zeros, ones, etc. to preallocate your arrays.
mysiak
mysiak 2019-11-8
For example when reading custom binary files.
I created simple binary file where all elements are of say 64bit long int64. Now I want to read such binary file in matlab with fread. I want to use fseek in order to navigate through the file, but I need to move in chunks of data which correspond to meaningful frame in my applicatio, say 5 numbers of int64.
So the fseek looks like fseek(fileid, 5*8, 'cof');
Then I use fread like fread(fileID,5,'int64')
Now it would be good if the 5*8 in fseek could be replaced by 5 *sizeof('int64') since matlab is aware of the int64 type. So the number 8 should be tied to int64 type.

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回答（3 个）

Birdman
Birdman 2018-3-28
Use the sizeof.m file from the following link:
https://www.mathworks.com/matlabcentral/fileexchange/16595-sizeof
Type:
sizeof('double')
Jan
Jan 2018-3-28
编辑：Jan 2021-4-13
A cheap method would be:
function S = sizeof(V)
switch lower(V)
case {'double', 'int64', 'uint64'}
S = 8;
case {'single', 'int32', 'uint32'}
S = 4;
case {'char', 'int16', 'uint16'}
S = 2;
case {'logical', 'int8', 'uint8'}
S = 1;
otherwise
warning('Jan:sizeof:BadClass', 'Class "%s" is not supported.', V);
S = NaN;
end
end
Horshack Horshack
Horshack Horshack 2021-4-10
编辑：Horshack Horshack 2021-4-12
Edit: Oops, this doesn't work in Matlab, only Octave.
I simply cast an arbitrary constant value (zero) to the type and then take the size of the lvalue result. Examples:
sizeof(uint8(0))
sizeof(uint16(0))
sizeof(uint32(0))
sizeof(double(0))
Output:
1
2
4
8

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