How to introduce boost::shared_ptr into an existing (large) C++ codebase?

Question

Hi,

I am currently trying to fix a few weaknesses in our code base by introducing the use of smart pointers. The code base is very large, and interlinked like a spider who's had one to many coffee's.

I was wondering if people had tried the before and what their approach was.

My first step has been to typedef classes, as follows.

#ifndef USE_SMART_POINTERS
    #define USE_SMART_POINTERS 0
#endif

#if USE_SMART_POINTERS == 1
    #include <boost/smart_ptr.hpp>
#endif


namespace ProductX
{
    // forward decleration
    class CTObject;


    //typedefs
    #if USE_SMART_POINTERS == 1
        typedef boost::shared_ptr<CTObject> CTObjectPtr;
    #else
        typedef CTObject* CObjectPtr;
    #endif
}

Now I realise this will lead to a wealth of compile areas, things like

CTObjectPtr i = NULL;

Will completly bork when smart pointers are enabled.

I was wondering if there was anything I could do at this early stage to reduce the mass of compile errors, or is it as I suspect just take things on a case by case basis.

Cheers Rich

Answer 1

Don't do this: the typedefs I mean.

Presumably the old code has at least some delete calls in it? Which would certainly fail in the case of a smart pointer.

Smart pointer certain things or not, i.e. chase a specific instance through the code base. Make it work, then move on. Good Luck!

Answer 2

Instead of trying to introduce smart pointers everywhere you could use the Boehm-Demers-Weiser garbage collector and leave your code base intact.

It will also take care of cyclic references.

Answer 3

There is no easy way to do this. As you've found out, boost::shared_ptrs and standard pointers are not interchangeable. What you are doing here is refactoring code, and unfortunately refactoring takes a long time and can be very tedious.

As sdg said, typedefing pointers for shared_ptrs is not a good idea, and just increases the amount of code you have to write.

First, I would identify the pointers that actually need to be changed to shared_ptrs. Obviously you don't want to be changing all pointers to shared_ptrs. Most would probably be better off as std::auto_ptrs or boost::scoped_ptrs and some would be better as boost::weak_ptr, and finally some might just be fine as plain C-style pointers.

Just go through each pointer that needs changing one-by-one, find all references to it, and make the necessary adjustments (e.g. removing calls to delete).

Answer 4

I would be very restrictive in introducing shared_ptr into an existing large codebase. If you really want to use smart-pointers to fix errors I suggest using scoped pointers and other than that I would refactor code and design clear ownership.