Refactoring with References and Pointers Tip

Inherited source code is a fact of life for any professional programmer.  Sometimes you inherit a 5000+ line C++ method chock full of pointers and pointers to pointers.

If you’re utilizing the copy-and-paste algorithm for refactoring large blocks of pointer and pointer-to-pointer riddled code then C++’s Pass by Reference support can make these changes much less painful.  Thankfully it supports References to Pointers!

So instead of taking a block similar to the following:

int *ptr = NULL;

if ( someCond )
    ptr = new int[len]; // we either allocate it here or leave it null

for (int i=0; i < len; i++)
{
    if ( ptr == NULL )
    {
        ptr = new int[len];
    }
    else
    {
        delete [] ptr;
        ptr = new int[len + i];
    }

    int x = ptr[i] * ptr[i + 1];
    // ... several hundred lines of code
}

and converting the loop into something unreadable, error prone and barely recognizable as the former loop body:

void SomeFunc(int** ptr, int len)
{
    for (int i=0; i < len; i++)
    {
        if ( (*ptr) == NULL )
            (*ptr) = new int[len];
        else
        {
            delete [] (*ptr);
            (*ptr) = new int[len + i];
        }

        int x = (*ptr)[i] * (*ptr)[i + 1];
        // ... several hundred lines of code
    }
}

You can convert the loop into something easily recognizable as the former loop ala:

void SomeFunc(int*& ptr, int len)
{
    for (int i=0; i < len; i++)
    {
        if ( ptr == NULL )
        {
            ptr = new int[len];
        }
        else
        {
            delete [] ptr;
            ptr = new int[len + i];
        }

        int x = ptr[i] * ptr[i + 1];
    }
}