Re: [ALACPP] smart pointers in C

[Christopher Smith <x@xxxxxxxx>]

Josh Dybnis wrote:

--- Christopher Smith <x@xxxxxxxx> wrote:
  

On Wed, 2003-07-02 at 07:43, Josh Dybnis wrote:
    

I don't think that it is possible to do smart pointers in C. The
reason why, is that there is no way in C to associate a piece of 
code with a value, in such a way that the code is automatically 
executed when the value is stored into a variable, or conversly 
when the value is taken out of a variable (either because the 
variable goes out of scope or another value is stored in it). In 
C++ this can be done with constructors, a destrutor, a copy 
constructor, and an overloaded assignment operator.
      

In C you can do smart pointers through the mechanisms like handles.
It's not as pretty as the C++ approach, but it works.
    

Can you elaborate on this, or give a reference?

Umm... pretty much any OS or GUI environment provides you with handles, which are typically some kind of an int which provides an indirect reference (typically through a lookup table of some kind) to the real pointer. Functions are provided for opening, copying (well, not always copying) and closing the handle. Each of the functions updates internal structures which manage the actual resources the handle is associated with, including ref-counts. Typically you never get direct access to the real data structure, although in some crazy cases the int's value is the same as the address value of the pointer. Because you are dealing with C instead of C++, using the copy operator will simply do a bitwise copy without updating any refs. Also, you don't have destructors, so you have to explicitly ensure that you close a handle before it falls out of scope.

Like I said, it isn't pretty, but it essentially provides a resource management abstraction.

--Chris