MATLAB中如何知道变量的大小

Question

我在 MATLAB 中有变量，我已经使用 class() 检查了它们的类，但我也想知道它们在内存中占用的大小。更准确地说，我知道它们是 double 类型，并且我想确保它们是 32 位 double 而不是 64 位。

我使用的MATLAB版本是R2009b。

Answer 1

我编写了一个简单的便利函数来处理这个问题。用法是：

>> x = ones(1000);
>> ByteSize(x)
7.63 Mb

我运行的是R2007a，所以Java对象不返回大小的问题可能已经在后续版本中得到修复。这是代码：

function ByteSize(in, fid)
% BYTESIZE writes the memory usage of the provide variable to the given file
% identifier. Output is written to screen if fid is 1, empty or not provided.

if nargin == 1 || isempty(fid)
    fid = 1;
end

s = whos('in');
fprintf(fid,[Bytes2str(s.bytes) '\n']);
end

function str = Bytes2str(NumBytes)
% BYTES2STR Private function to take integer bytes and convert it to
% scale-appropriate size.

scale = floor(log(NumBytes)/log(1024));
switch scale
    case 0
        str = [sprintf('%.0f',NumBytes) ' b'];
    case 1
        str = [sprintf('%.2f',NumBytes/(1024)) ' kb'];
    case 2
        str = [sprintf('%.2f',NumBytes/(1024^2)) ' Mb'];
    case 3
        str = [sprintf('%.2f',NumBytes/(1024^3)) ' Gb'];
    case 4
        str = [sprintf('%.2f',NumBytes/(1024^4)) ' Tb'];
    case -inf
        % Size occasionally returned as zero (eg some Java objects).
        str = 'Not Available';
    otherwise
       str = 'Over a petabyte!!!';
end
end

Answer 2

您可以使用 whos 来获取描述等的结构数组things，每个变量的大小（以字节为单位）。

请注意，根据定义，双精度数是 64 位！

Answer 3

dt=whos('VARIABLE_YOU_CARE_ABOUT'); MB=dt.bytes*9.53674e-7;  

这将为您提供以兆字节为单位的大小，例如 MB=123.78

Answer 4

我尝试增强“MatlabSorter”的简单功能来处理这个问题。用法仍然相同：

>> x = ones(1000);
>> getByteSize(x)
7.63 mb

补充：

1.您可以说明您寻求哪种类型的返回 - b、kb、mb、tb 或 pb

2.您可以将结果作为变量获取，而无需将其打印在屏幕上

这是代码：

function b = getByteSize(theVariable, returnType, fid)
% getByteSize returns the mem.usage of the provided variable(theVariable) to the given file
% identifier. 
% returnType is assigned meaningfully according to the byte size if not stated
% Output is written to screen if fid is 1, empty or not provided.
s = whos('theVariable');
b = s.bytes;
if nargin == 1 || isempty(returnType)
    scale = floor(log(b)/log(1024));
    switch scale
        case 0
            returnType = 'byte';
        case 1
            returnType = 'kb';
        case 2
            returnType = 'mb';
        case 3
            returnType = 'gb';
        case 4
            returnType = 'tb';
        case -inf
            % Size occasionally returned as zero (eg some Java objects).
            returnType = 'byte';
            warning('Size occasionally returned as zero (eg some Java objects). Bytes assumed');
        otherwise
            returnType = 'petabytes';
            warning('Over 1024 petabyte. petabytes assumed');
    end
end
switch returnType
    case {'b','byte','bytes'}
        b = s.bytes;
    case {'kb','kbs','kilobyte','kilobytes'}
        b = b / 1024;
    case {'mb','mbs','megabyte','megabytes'}
        b = b / 1024^2;
    case {'gb','gbs','gigabyte','gigabytes'}
        b = b / 1024^3;
    case {'tb','tbs','terabyte','terabytes'}
        b = b / 1024^4;
    case {'pb','pbs','petabyte','petabytes'}
        b = b / 1024^5;
    otherwise
        returnType = 'bytes';
end
if nargin <= 2 || isempty(fid) || fid == 1
    fprintf(1,[num2str(b) ' ' returnType '\n']);
elseif nargin > 2 && ~isempty(fid) && fid > 2
    try
        fprintf(fid,[num2str(b) ' ' returnType '\n']);
    catch
        warning(['fid(' num2str(fid) ') could not be edited. Hence the output will be written on the screen.']);
        fprintf(1,[num2str(b) ' ' returnType '\n']);
    end
end
end

Answer 5

另一种使用 whos 函数的班轮

x=1;
Nbytes=getfield(whos('x'),'bytes')

Answer 6

您还可以显示工作区本身中变量的字节大小。

1. 找到工作区。
2. 单击工作区标题栏中的箭头图标。
3. 将鼠标悬停在“选择列”上。
4. 单击“字节”。