convert jagged array of System::Byte to unsigned char**

Question

I would like to implement a C++\CLI function that convert a jagged array of System::Byte to unsigned char**. I made this:

unsigned char**     NUANCECLR::IsItYou::convertBBtoCC(array<array<System::Byte>^>^ b)
{
    unsigned char** x = NULL;
    for (size_t indx = 0; indx < b->Length; indx++)
    {       
            if (b[indx]->Length > 1)
            {
                pin_ptr<System::Byte> p = &b[indx][0];
                unsigned char* pby = p;
                char* pch = reinterpret_cast<char*>(pby);
                x[indx] = reinterpret_cast<unsigned char *>(pch);
            }
            else
                x[indx] = nullptr;
    }
    return x;
}

I can't test it currently, maybe someone can help me, tell me if it is ok or not, because I need it relatively fast.Thank you!

Answer 1

Not OK. This will bow up in your face a number of different ways:

unsigned char**     NUANCECLR::IsItYou::convertBBtoCC(array<array<System::Byte>^>^ b)
{
    unsigned char** x = NULL; 

No storage allocated. x[anything] will be invalid.

    for (size_t indx = 0; indx < b->Length; indx++)
    {       
            if (b[indx]->Length > 1)
            {
                pin_ptr<System::Byte> p = &b[indx][0]; 

this pining pointer will go out of scope at the end of this if block and unpin. The system may once again move or delete at will

                unsigned char* pby = p;

This takes a pointer to an array of object wappers around a byte and assigns it to an array of char. I won't claim expertise here, but I don't believe this will work transparently without a lot of hidden voodoo.

                char* pch = reinterpret_cast<char*>(pby);

This will actually work, but becasue the previous likely doesn't, I don't expect pch to point at anything meaningful.

                x[indx] = reinterpret_cast<unsigned char *>(pch);

As stated above, x doesn't point at any storage. This is doomed.

            }
            else
                x[indx] = nullptr;

also doomed

    }
    return x;

and still doomed.

}

Recommendation:

1. Allocate unmanaged storage with new for a char * array of size b->Length and assign to x
2. Allocate unmanaged storage with new for a char array of size b[indx]->Length and copy all of the elements of b into it, then assign to x[indx].
3. return x
4. ensure all the arrays pointed to by x and then x are deleted when you're done with them. Or use vector<vector<char>> instead of char**.