C++ nested struct with dynamic array in healer file

Question

I'm trying to define a bunch of structs in a header file. For example:

struct Firststruct{
    int useless;
};

struct Secondstruct{
    Firststruct* struct1;    // we want to have a dynamic array here.    
};

struct Thirdstruct{
    Secondstruct* struct2;    // we want to have a dynamic array here.    
};

And for simple usage in main or source file. We want to define the struct constructor. For example:

struct Secondstruct{
    Firststruct* struct1;    // we want to have a dynamic array here. 

    // constructor
    Secondstruct(int num_struct1){
        struct1 = new Firststruct[num_struct1];
    };

    // deconstructor
    blablabla
};

So here is the question, how could we define the constructor in Thridstruct?

struct Thirdstruct{
    Secondstruct* struct2;    // we want to have a dynamic array here. 

    // constructor
    Thirdstruct(int num_struct2){
        struct2 = new Secondstruct[num_struct2];    // this of couse does not work. 
    };

    // deconstructor
    blablabla
};

I am new in C++, so I do not know how to write it. Could someone provide some ideas?

Thanks. :)

@ArminMontigny No. And by posting your answer as a comment you've dodged peer review so I cannot downvote your wrong answer to mark it as wrong for others. Please don't do that. — Asteroids With Wings
– Asteroids With Wings, Commented Apr 24, 2020 at 10:20
Does this answer your question? Object array initialization without default constructor — Asteroids With Wings
– Asteroids With Wings, Commented Apr 24, 2020 at 10:21

eerorika · Accepted Answer · 2020-04-24 10:18:07Z

3

Option 1: make Secondstruct default constructible by defining a default constructor.

Option 2: do not create a dynamic array of Secondstruct directly, but instead a dynamic array of raw bytes of sufficient size. Then reuse the storage with std::uninitialized_fill.

Best option: Use std::vector instead which does the complicated sounding thing of option 2 as well as lacks the memory leaks and undefined behaviour that the custom attempt of implementing dynamic array is undoubtedly going to suffer from.

answered Apr 24, 2020 at 10:18

eerorika

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