Actually, the new() operator isn't a storage allocator, it's a storage
locator. You can write your own memory manager (like hal_malloc) to
decide where to put things. It's just that the default new operators
also happen to allocate space before telling the caller a location -
it's the easiest way to guarantee that there's storage for the object.
An interesting application for that feature is to have a new() operator
for a class representing a piece of memory-mapped hardware. You make
the data layout match the hardware, and overload new() to point to the
physical memory address of the hardware. The vtables and other assorted
"behind-the-scenes" data are kept in a different place (function
pointers are managed on a class basis, not an instance basis - at least
for non-virtual classes), so you don't have to worry about c++ screwing
around with the hardware.
Note - I'm only pointing out some interesting language applications, I'm
not suggesting that HAL be rewritten in c++ (yet :) ).
- Steve
ben lipkowitz wrote:
>On Wed, 10 Oct 2007, Kenneth Lerman wrote:
>
>
>>I'm very comfortable using the standard C libraries, but have concerns about
>>using the C++ class libraries. Specifically, I'm concerned that their use of
>>memory might be somewhat less deterministic than the rest of emc. In a
>>previous life involving other projects of this nature, I heard strong
>>arguments both for and against using such libraries. I purposely avoided
>>using the map class in my code.
>>
>>Ken
>>
>>
>
>I'm not too familiar with C++ memory allocation, but I thought I'd share
>this nifty hack, courtesy of pete vavaroutsos:
>
>#ifdef __cplusplus
>// Overloaded new operator used to call constructors explicitly without
>// memory allocation. This prevents dynamic reallocation of memory which can
>// cause problems if we request memory that is not available - not a good
>// situation to be in when you are rapidly moving chunks of iron around.
>inline void *operator new (size_t s, void *ptr) { return(ptr); }
>inline void *operator new [] (size_t, void *ptr) { return(ptr); }
>
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