c ++ Data entry and read back to array in struct structure in list

Question

I'd like to simply ask you about something i can't solve in the algorithm I'm designing. I'm asking a question that's purely learning. I searched both stackoverflow and Uncle Google, but I didn't see a logical solution.

 struct MyStruct_1
{
    int number[];
};

Imagine it's such a struct Or imagine that there are a few other things in it that aren't arrays.

 struct MyStruct_2
{
    int  id;
    string ModelName;
    int number[];
};

**Insert ==>>>  ID = 1 ModelName = "ModelA" number = { 6,7,8,9, 57 }
Insert ==>>>  ID = 2 ModelName = "ModelB" number = { 3,17,9,28,8 }
*****************************************************************
Update/Delete ==>>>  ID = 2 ModelName = "ModelB" number = { 9 }
Update/Delete ==>>>  ID = 1 ModelName = "ModelA" number = { 57 }
*****************************************************************
Insert/Add ==>>>   ID = ModelName = "ModelA" number = 103**

In this way, from a structure to a C++ language;

list<MyStruct> demoListe

when I create

My 1st question: how do we provide data entry? push_back ({ 9,3,65,2 }); I tried it, but I got an error message.

My 2nd question: Can the friend who answers the data to enter the data also sample reading the data?

I'd like to thank everyone who will help and lead me to the right solution.

Regards

@TedLyngmo What is a viable solution to overcoming prohibitions or complying with prohibitions? — Umit Terzi
– Umit Terzi, Commented Jan 1, 2020 at 20:40
What is a viable solution to overcoming prohibitions or complying with prohibitions? — Umit Terzi
– Umit Terzi, Commented Jan 1, 2020 at 20:53
I put that in the first sentence of my answer below :-) Use a std::vector instead. — Ted Lyngmo
– Ted Lyngmo, Commented Jan 1, 2020 at 20:57

amirali · Accepted Answer · 2020-01-01 20:41:38Z

2

Note that this code is OK:

struct st
{
   int id;
   string s;
};

vector<st> v;

v.push_back({1, "abc"});

But you can't initialize array with {}, So use Vector Container:

struct st
{
   int id;
   string s;
   vector<int> v;
};

vector<st> u;

u.push_back({1, "abc", vector<int>{1, 1, 2}});

answered Jan 1, 2020 at 20:41

amirali

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5 Comments

Umit Terzi Over a year ago

Can't vector be a solution using just STRUCT and LIST without using it? Thank you very much for the reply

amirali Over a year ago

@UmitTerzi Do you mean not to use vector? Of course. Just replace every vector with a list.

Umit Terzi Over a year ago

Yes, I meant not to use Vector. But without knowing the job, I ask, what do you think is better in terms of performance, which is the solution to do it using lists instead of vector?

Ted Lyngmo Over a year ago

@UmitTerzi Which one to choose depends on the use-case. For most use-cases, std::vector is preferred.

amirali Over a year ago

@UmitTerzi It depends. Vectors are different from lists. Different works, different capabilities, and different usages. You can see cplusplus.com, Or ask a new question to get more info.

Ted Lyngmo · Accepted Answer · 2020-01-01 21:50:31Z

1

Flexible arrays are forbidden in standard C++. You should use a std::vector instead:

#include <algorithm>
#include <iostream>
#include <iterator>
#include <list>
#include <vector>
#include <string>

struct MyStruct
{
    int id;
    std::string ModelName;
    std::vector<int> number;
};

int main() {
    // initialized with a few numbers
    MyStruct ms{1, "model", {2,3,4}};

    // push_back a new number
    ms.number.push_back(5);

    // print the numbers
    for(int value : ms.number) {
        std::cout << value << '\n';
    }

    // or make a std::list<MyStruct>
    std::list<MyStruct> demoListe {
        {1, "model_a", {2,3,4}},
        {2, "model_b", {5,6,7,8}}
    };

    // add a model
    demoListe.emplace_back(MyStruct{3, "model_c", {11,22}});

    // add 99 to model_a
    auto ait = std::find_if(demoListe.begin(), demoListe.end(), 
                            [](const MyStruct& ms) { return ms.id==1;} );
    if(ait != demoListe.end())
        ait->number.push_back(99);

    // remove 7 from model_b
    auto bit = std::find_if(demoListe.begin(), demoListe.end(),
                            [](const MyStruct& ms) { return ms.id==2;} );
    if(bit != demoListe.end()) {
        auto seven = std::find(bit->number.begin(), bit->number.end(), 7);
        if(seven != bit->number.end())
            bit->number.erase(seven);
    }

    // print result
    for(const MyStruct& ms : demoListe) {
        std::cout << "id: " << ms.id << " model: " << ms.ModelName << '\n';
        std::copy(ms.number.begin(), ms.number.end(),
                  std::ostream_iterator<int>(std::cout, " "));
        std::cout << '\n';
    }
}

edited Jan 1, 2020 at 21:50

answered Jan 1, 2020 at 20:42

Ted Lyngmo

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6 Comments

Umit Terzi Over a year ago

Thank you for the reply. What I don't understand is ms.number.push_back(5); {1, "model_a", {2,3,4}}, {2, "model_b", {5,6,7,8}} If I wanted to add 99 to the "model a" which is ID = 1 here, and at the same time What if I want to delete 7 from "model b" which is ID = 2? How does it work?

Umit Terzi Over a year ago

Lyngmo I updated by adding the example I wanted to ask . Thank you so much.

Umit Terzi Over a year ago

I'm trying it right now. I didn't update the page when I wrote it

Umit Terzi Over a year ago

I've tried what you've written, thank you very much. But if I wanted to add a new model, there was a problem. demoListe.insert (3, "Model_C", { 31,32,33,34,35 }); I couldn't log in like this, do I have to use a different method?

Umit Terzi Over a year ago

godbolt.org/z/cQ9jpH ............ Thank you so much for everything. I'm going to learn and improve by studying the code you've written in detail.

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