C ++访问冲突写入位置0x00000000

Question

I have the following code: In Client.cpp there is the constructor that is doing memory allocation for the array "conturi" of type ContBancar.

Client::Client(string nume, string prenume, string adresa)
{
    this->nume = nume;
    this->prenume = prenume;
    this->adresa = adresa;
    nrCont = 0;
    ContBancar** conturi = new ContBancar*[50]; 
}

Then there is a method that is adding a account in the "conturi" array:

void Client::adaugaCont(ContBancar* contNou)
{
    conturi[nrCont++] = contNou;
}

This is my code in Main.cpp:

ContBancar ron1 ("1.r", 0, Banca::RON);
Client ioana ("Pop", "Ioana", "Str Dorobantilor 3/4");
ioana.adaugaCont(&ron1);

But it gives me the access violation error at runtime, like the array 'conturi' has no memory allocated. I don't understand why, because the memory should be allocated in the constructor.

Could anyone help me with this?

Answer 1

Client::Client(string nume, string prenume, string adresa)
{
    this->nume = nume;
    this->prenume = prenume;
    this->adresa = adresa;
    nrCont = 0;
    //here is your problem!
    ContBancar** conturi = new ContBancar*[50]; 
}

You redefine conturi as a new array, with the pointer to it stored in the local scope of the constructor.

Change the line to:

conturi = new ContBancar*[50]; 

and you will then have the object's conturi pointer pointing to the allocated memory.
This will also solve the memory leak you have introduced.
(pointer to heap goes out of scope. memory on heap is leaked)

Or even better, use a std::vector.
In Class definition:

std::vector<ContBancar> conturi;

You don't have to manage the memory yourself with new and delete and you are not restricted to a fixed number of elements either.

Answer 2

You're declaring a new pointer variable with the following line:

ContBancar** conturi = new ContBancar*[50]; 

and the pointer variable will get destroyed at the end of the function call and leak memory leaving any other same-name member variable untouched.

You should rather use the member variable conturi (assuming you have one from the rest of the code):

Client::Client(string nume, string prenume, string adresa)
{
    this->nume = nume;
    this->prenume = prenume;
    this->adresa = adresa;
    nrCont = 0;
    conturi = new ContBancar*[50];
}

or you can use a std::vector<ContBancar> conturi member variable which might be easier to use and to deal with.

This is a simple reproducer to better understand the problem:

class Client {
public:
    int** conturi = 0;

    void function() {
        int** conturi = new int*[50];
    }
};

int main()
{
    Client obj;
    obj.function();
    if(obj.conturi == 0)
       std::cout << "this is still zero"; // This will get printed
}

Example