pointer to pointer dynamic array in C++

Question

I've been having bad luck with dynamic pointers when I want to close it. why the application wrote to memory after end of heap buffer? how can I close my array?

int main()
{
    .
    .   
    int **W;
    W = new int* [n];
    for (int i=1; i <= n; i++)
        W[i] = new int[n];
    .
    .
    .
    ast(n,W);

    for(int i = 1; i <=n ; i++)
    {
        delete W[i];
    }
    delete W;
    getch();
}
void ast (int n,int **W)
{
    int **D;
    D = new int* [n];
    for (int i=0; i < n; i++)
        D[i] = new int[n];

    D=W;
    for (int k=1;k<=n;k++)
        for (int i=1;i<=n;i++)
            for (int j=1;j<=n;j++)
                D[i][j]=min(D[i][j],D[i][k]+D[k][j]);
    .
    .
    for(int i = 1; i <=n ; i++)
    {
        delete D[i];
    }
    delete D;
}

You should loop from 0 to n-1 instead of 1 to n. Better still, use std::vector. — Abhishek Bansal
– Abhishek Bansal, Commented Jun 22, 2015 at 9:32
@illusionist_yahya You're working with "dynamic arrays" and you were not aware that (even simple) arrays start at index 0? — PaulMcKenzie
– PaulMcKenzie, Commented Jun 22, 2015 at 9:40

Vlad from Moscow · Accepted Answer · 2015-06-22 09:38:51Z

2

The valid range of indices of an array with N elements is [0, N-1]. Thus instead of for example this loop

for (int i=1; i <= n; i++)
         ^^^^ ^^^^^^

you have to write

for ( int i = 0; i < n; i++ )

As you used operator new [] you have to use operator delete [] So instead of

for(int i = 1; i <=n ; i++)
{
    delete W[i];
}

and

delete W;

you have to write

for ( int i = 0; i < n; i++ )
{
    delete [] W[i];
}

and

delete []W;

Function ast does not make sense because apart from other errors it has a memory leak. At first you allocate memory and assign its address to pointer D and then you overwrite this value of the pointer

void ast (int n,int **W)
{
    int **D;
    D = new int* [n];
    for (int i=0; i < n; i++)
        D[i] = new int[n];

    D=W; // <== ???

answered Jun 22, 2015 at 9:38

Vlad from Moscow

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