Why do I receive "Cannot write value: unsupported class struct error" when writing a structure using the FWRITE function?
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If I try to write a structure to a file using the FWRITE function, i receive the following error:
??? Error using ==> fwrite
Cannot write value: unsupported class struct
For example:
a.name='Mathworks';
a.number=10;
fid = fopen('testfile.txt','w+');
fwrite(fid,a)
采纳的回答
MathWorks Support Team
2009-6-27
The ability to write a structure to a file using FWRITE is not available in MATLAB.
To work around this issue, write each field of the structure sequentially to the file. This can be done either by calling the FWRITE function from the command line for every field, or by writing a program similar to the one shown below to loop through each variable and write it to the file:
%%%Open the file in the write mode, fid is the id of the file.
%%%Assume the structure is the variable ‘a’
%%%As a sample, let ‘a’ have two fields: name and number
a.name='Mathworks';
a.number=10;
NEWLINE = sprintf('\n');
fields=fieldnames(a);
for i=1:length(fields)
fields(i);
classes{i}=eval(['class(a.' fields{i} ')']);
end
fid = fopen('testfile.txt','w+');
for j = 1: length(fields)
if ~strcmp(classes(j),'char')
str = num2str(eval(['a.' fields{j} ]));
else
str = eval(['a.' fields{j} ]);
end
fwrite(fid, str, 'uchar');
end
fwrite(fid, NEWLINE, 'char');
%%%Call this loop if you have multiple structures too.
%%%Close the file.
1 个评论
Vandana Ravichandran
2017-2-22
编辑：MathWorks Support Team
2023-4-26
MATLAB converts .NET object to native MATLAB data types. In your case, System.Int64 should be converted to int64 scalar. Refer the following page from the documentation for more information: https://www.mathworks.com/help/matlab/matlab_external/handling-net-data-in-matlab.html
If you just want to save the workspace structure variables for future use inside MATLAB, you can use the "save" function. If you want to save the structure to a text file, you can convert the structure array to a table using "struct2table" function. Subsequently, you can use "writetable" function to write the table to a comma-delimited text file.
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