Clearing a 2d pointer vector of class objects

[AkshayMalige]

Hello,
How do I clear a 2d pointer vector of class objects.

Ex: std::vector< vector<SttHit*>* >* vec_layer;

vec_layer->clear();
or
vec_layer->erase (vec_layer->begin(),vec_layer->end());
gives me a segmentation break.

[Handy Andy]

Hello AkshayMalige,

Try vec_layer.clear().

Andy

[AkshayMalige]

Hey Andy,

It doesn't work since that is a pointer.

[Enoizat]

I’d give a second check to my destructor - perhaps there’s something which is not deleted properly.
Just out of curiosity, does a two steps ‘clear()’ works?

Example:

#include <chrono>
#include <iostream>
#include <vector>
#include <random>


using weird_vec = std::vector<std::vector<int*>*>;


void printWeirdVector(const weird_vec* v);


int main()
{
    constexpr int Max_Vect_Size { 10 };
    std::mt19937 eng {
        static_cast<unsigned>(
            std::chrono::high_resolution_clock::now().time_since_epoch().count()
        )
    };
    std::uniform_int_distribution<> dst(0, Max_Vect_Size - 1);

    weird_vec *vec_layer = new weird_vec(Max_Vect_Size);

    for(auto& a : *vec_layer) {
        a = new std::vector<int*>(Max_Vect_Size);
        for(auto& b : *a) {
            b = new int { dst(eng) };
        }
    }

    // Only for debug: print out the container
    printWeirdVector(vec_layer);

    for(auto& a : *vec_layer) {
        a->clear();
        // a->shrink_to_fit() ?
    }
    vec_layer->clear();
    // vec_layer->shrink_to_fit() ?

    // Is there anything to print out?
    std::cout << "Printing out the container:\n";
    printWeirdVector(vec_layer);
}


void printWeirdVector(const weird_vec* v)
{
    
    for(const auto& a : *v) {
        for(const auto& b : *a) {
            std::cout << *b << ' ';
        }
        std::cout << '\n';
    }
    std::cout << '\n';
}

[mbozzi]

It would probably be best to eliminate the pointer-to-vector-of-pointers-to-vectors-of-pointers entirely.

Why, in particular, is std::vector<std::vector<SttHit>> not suitable for the use case?

[AkshayMalige]

Thank you for your interest mbozzi,

It is quite difficult for me to use just a vector instead of a pointer since i have function that is repeated some million times on this vector which demands a pointer.

Is there any other way to clear it as it is?

[mbozzi]

It is quite difficult for me to use just a vector instead of a pointer since i have function that is repeated some million times on this vector which demands a pointer.

I don't understand why. You can obtain a pointer to the elements of the vector as required.

[AkshayMalige]

Okay, I am not an expert, hence i am taking your suggestion and going ahead with it. I will let you know my results with this. Thank you

[AkshayMalige]

Turns out my code works without using pointers. Thank you very much for the idea mbozzi