"Structure field undefined on some execution paths" error when copying data between cell arrays

I am trying to generate C code for a simple function with MATLAB Coder. This function defines a structure "out" and includes the following code: 

if ~isempty(data)
    date=cell(length(data),1);
    for i=1:length(data)
       date{i,1} = data{i,1};
    end
    out.date=date;
end

I get the following error message during code generation runtime issue check stage:

"Structure field 'out.date{:}' is undefined on some execution paths."

My function is written in a way such that this field should always be defined. Why is this error occurring, and how can I work around it?

Answer 1

[MathWorks Support Team]

This error can be resolved by always assigning the variable "out.date", even when data is empty. When data is empty, you should assign "out.date" to a default value, such as an empty cell array. When data is not empty, assign it as usual. Additionally, for better compatibility with MATLAB Coder, it is recommended to store "length(data)" in a variable before using it in a loop. Here is how you can structure your code:

if ~isempty(data)    N = length(data);    date = cell(N,1);    for i = 1:N        date{i,1} = data{i,1};    end    out.date = date;else    out.date = cell(0,1);end

[Walter Roberson]

Isn't the real problem that out.date is not defined in the case where isempty(data) ?