Passing a reference to a pointer to pointer of type void

Question

I have a function that accepts a reference to void**.

bool boExecute(void**& vOutParameter);

I tried to write some value in vOutParameter, but when I checked it in the main(), the value was not written.

In this case, what does & referencing to? Is it a reference to a pointer or a reference to a pointer to pointer?

Inside boExecute, I add it like this:

bool boExecute(void**& vOutParameter)
{
    Struct_Type* Out = new Struct_Type[4];
    for (int i=0; i<4; ++i)
    {
        memcpy(&(Out[i]), Referenced_Struct[i], sizeof(Struct_Type));
    }
    *vOutParameter = reinterpret_cast<void*>Out;
    Out = null;
    return true;
}

Referenced_Struct is of type Struct_Type**, which had two members, int32_val and int64_val.

Contents of main:

void main(void)
{
   void **test;
   boExecute(test);
   Struct_Type** temp = reinterpret_cast<Struct_Type**>(test);
   Struct_Type* temp1 = *temp;
   for (int i=0; i<4; ++i)
   {
       printf("%d, %d", temp1[i].int32_val, temp1[i].int64_val);
   }
}

Is there something wrong in what I'm doing? When I changed *vOutParameter, the contents of *vOutParameter should be updated when it goes out of the function, right?

Answer 1

Is there something wrong in what I'm doing?

You should rewrite the function actually using C++, instead of weird C semantic with unnecessary boolean return values for errors and out parameters:

template<typename It>
std::vector<Struct_type> boExecute(It Reference_begin, It Reference_end)
{
    std::vector<Struct_type> Out;
    std::copy(Reference_begin, Reference_end, std::back_inserter(Out));
    return Out;
}

Live demo

Notice that there's no performance issue in returning the whole vector because of RVO (Return Value Optimization). So you can sleep knowing that your memory is safe.

---

In this case, what does & referencing to? Is it a reference to a pointer or a reference to a pointer to pointer?

In general T& is a reference to T . Which means that void**& is a reference to a void** which is a pointer to pointer to void .