Question

I have an array of type T which I pass as a pointer parameter to a function.
The problem is that I can’t write new data to this array properly, without getting memory violation at the second try.

In this code I read integers from a text file and pass them to the function (part of template class of type T), in order to append them to the array.

After I finish to append the integers, I want to use the same array back in the Main.

Does someone know what’s wrong with the code?

Thanks, Max

template<class T> int CFile<T>::read(T **apBuf, int aNum)
{
int readCounter = 0;

*apBuf = (T*)malloc(sizeof(T)*aNum);


for (int i = 0; i<aNum; i++)
{
    T var = read();

    if (var == NULL)
    {
        if (isEof)
        {

            return readCounter;
        }
        else
        {
            perror ("Error Reading File - Insufficient var type");
            return -1;
        }
    }
    else
    {   
        *apBuf[i] = var;

        readCounter++;
    }
}



return readCounter;

}

Answer 1

*apBuf[i] = var;

This is parsed as if it was written:

*(apBuf[i]) = var;

This is obviously not what you want; apBuf is a pointer to a pointer to an array; you are treating it as a pointer to an array and you are dereferencing the ith element of it. What you really mean is:

(*apBuf)[i] = var;

*apBuf gives you “the object pointed to by apBuf,” which is the array; then you obtain the ith element of the array.

That said, this is rather unusual: why not accumulate the data into a std::vector<T> and return that from the function? Then you don’t have to worry about the explicit dynamic memory management. (Also, is T always a pointer type? If not, then var == NULL makes no sense.)