NSMapTable C function API equivalent
NSMapTable C function API equivalent
- Subject: NSMapTable C function API equivalent
- From: George King <email@hidden>
- Date: Mon, 1 Jun 2009 12:29:10 -0700
I just read in the NSMapTable Class Reference that I can use the class
to map to and from pointers to C structs:
You can configure an NSMapTable instance to operate on arbitrary
pointers and not just objects, although typically you are encouraged
to use the C function API for void * pointers. The object-based API
(such as setObject:forKey:) will not work for non-object pointers
without type-casting.
Can somebody point me to the documentation for the "C function API"
referred to above? I was hoping to find a CFMapTable but I suppose
that would be too obvious :)
Are there any known simple examples of using NSMapTable with C
pointers as keys?
As for type casting, does this simply mean that I need to cast my key
and value C pointer types to id in order for the compiler to accept
them as message arguments?
My particular use case is that I have a simple pair struct that
consists of two unsigned ints, which I use as a key to look up an
NSArray. I could use a std::map with NSArray* as the value type, and
ignore the objective-c retain/release semantics for the NSArray
pointers in the map, but I'd prefer to respect those. Currently I'm
converting the pair struct into an NSNumber for use as a key in an
NSDictionary, which seems to work OK, but I'm concerned that all the
autoreleased NSNumbers are going to pile up. Rather than start
creating and draining pools, I would prefer to avoid the temporary key
instances altogether. This is a performance-sensitive lookup in both
time and space; it remains to be seen whether Cocoa hash tables or stl
map trees are more efficient.
Thanks!
George
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