New fields cannot be added when structure has been read or used, MATLAB coder.

Hi,

I am trying to convert my matlab project into C++ using MATLAB Coder. I have a Class and in the constructor, I am initializing all the values of the struct that I have declared in the properties. The code goes something like this.

classdef ZCNET
   
    properties
       ZCNET_cfg;
       z_own_turbo_param_2bit_base;
       trellis;
       
    end
    
    methods
       
        function self = ZCNET()
    self.ZCNET_cfg.AP_ANT_NUM = 1;  
    self.ZCNET_cfg.NODE_ANT_NUM = 1;  
    self.ZCNET_cfg.useLTETurbo = 1;
    self.ZCNET_cfg.USE_SIMIC = 1;

    self.ZCNET_cfg.ANT_NUM = self.ZCNET_cfg.AP_ANT_NUM;
    if 1
        load_perm = load ('ZCNET_permutations.mat'); % NOTE: to get load_perm.ZCNET_permutations. load_perm.ZCNET_permutations{100} has a random permutation of 100 numbers
    else
        for h=1201:1500
            load_perm.ZCNET_permutations{h} = randperm(h);
        end
        load_perm.ZCNET_permutations_rev = cell(1,length(load_perm.ZCNET_permutations));
 
        .
        .
        .
        .
        .
        

        

Since I cannot convert a class directly, I have this function that create an object of the class and them I am using the object to display some valies. This is a test code in order to fix this issue. The function looks something like this.

function call_zcnet()
    zc1 = ZCNET;

    x = zc1.ZCNET_cfg;
    
    disp(x.bandwidth);
    disp(x.permutations{1,5});
    
end

I am passing "call_zcnet.m" to the coder but when it is giving quiet a few errors. I can run the code by callign 'call_zcnet' from the command window without any problem but coder is giving me following run-time issues.

Any help is appreciated.

Thank you.

[Denis Gurchenkov]

Hi Raghav, the screenshot you created does not contain the actual text of the errors.

Maybe you can just attach a zip file with all the files that one needs in order to reproduce the error? It'll be easier for someone to offer suggestions if the issue can be reproduced.

[Raghav Rathi]

Hi @Denis Gurchenkov, Thanks for getting back to me. I have created a simpler version of the code that I am attaching in a zip file. I am trying to initialize a struct in this class but according to the defination, MATLAB does not allow to define structs and other data structures. I also refered this post (https://www.mathworks.com/matlabcentral/answers/223848-how-to-use-structures-as-properties-of-a-matlab-class#answer_182706) I can do something like this, but the struct I am having is more than 100 fields which contains other structs and cell in it.

It would be great if you could help me with this problem.

Answer 1

[Darshan Ramakant Bhat]

If you want to make this class codegen compatible, you will have to make the field as a struct type. Below is a sample modified code ;

classdef ZCNET
   
    properties
       ZCNET_cfg = struct('AP_ANT_NUM',1,'NODE_ANT_NUM',3,'useLTETurbo',1,'USE_SIMIC',1);
       
    end
    
    methods
       
        function self = ZCNET() %constructor
            self.ZCNET_cfg.AP_ANT_NUM = 1;  
            self.ZCNET_cfg.NODE_ANT_NUM = 3;  
            self.ZCNET_cfg.useLTETurbo = 1;
            self.ZCNET_cfg.USE_SIMIC = 1;
            
            
        end
    end
end

Hope this will be helpful.

[Raghav Rathi]

Hi @Darshan Ramakant Bhat, Thanks for your suggestion but, like I mentioned here https://www.mathworks.com/matlabcentral/answers/857060-new-fields-cannot-be-added-when-structure-has-been-read-or-used-matlab-coder#comment_1585065 I have already tried it and it works, but then the struct (ZCNET_cfg) I am using is having contains more than 100 fields and some of them are cell arrays. I tried to define empty cell array like this,

ZCNET_cfg = struct('ZC_cell_array', cell(1,8))

But this does not work. That is the reason why, I am trying to define the fields in the constructor.

Is the only way to define a structure in a class is what you mentioned? If so, then I will have to structure my project which will be a pain. Thank you for the help.