Is there a use for uninitialized pointers in C or C++?

Question

In one of the comments in this question, it was brought out that initializing C++ pointers by default would break compatibility with C.

That's fine, but why would something like this matter? I would think the only time it would actually matter is if I wanted an uninitialized pointer for some reason. But I can't think of a reason why I would want to have that.

Is there a use for uninitialized pointers? Or is the compatibility issue merely one of compatible behavior (i.e., not increasing overhead) and not one of breaking code?

Answer 1

This is a very specialized optimized case for Video Games (basically an embedded system). We used to use them for Load-In-Place data behavior in our Video Games to speed up loading (and avoid fragmentation).

Basically we would create console-side (Playstation) objects in a PC cooker. Then to reduce fragmentation overload, we would pack the data objects in a contiguous buffer with a single alloc. References to the data objects in this buffer would then be changed to subtract the base from pointers to offsets (unfix call -- we also had a virtual fix / unfix calls that took the buffer base and could convert between offsets and pointers).

When we loaded the data, it loaded in one large block. All data referenced by the root was off the root object. We could do an inplace "new" on the the root that would initialize the proper VF tables for the object and fixup all the attached blocks (by doing inplace new and then fixing up attached blocks respectively).

We needed the constructors called (in place new) to generate the proper VF-Tables in the objects. However, if the pointers were automatically cleared to NULL during the constructor, we would have lost the offset data and not been able to recreate the pointers between the objects within the contiguous block.

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FWIW, this is a common technique in the Video Game world. This Gamasutra article (not written by me or my coworkers) explains in detail the similar thing they did at another company:

Also, this topic of discussion on SourceForge.

There have even been several GDC (Game Developer Conference) talks on the subject.

Searching on Google for "load-in-place" will give many other examples of people using this technique that basically requires uninitialized pointers.

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NOTE: Currently, this is the only response that actually answers the question asked ("Is there a use for uninitialized pointers in C or C++?") by giving a specific use for pointers that must remain unitialized.

All the other responses are better answers for the original question referenced ("[C++] Why aren’t pointers initialized with NULL by default?") that caused the poster to ask this question.