Glynn Clements wrote:
Peter Simons wrote:
When I create a CString with Foreign.C.String.newCString, do
I have to 'free' it after I don't need it anymore? Or is
there some RTS magic taking place?
How about Foreign.Marshal.Utils.new and all those other
newXYZ functions?
Yes. The new* functions allocate the memory with malloc, and you have
to free it yourself. OTOH, the with* functions allocate the memory
with alloca, and it is freed automatically. [...]
Just to be nitpicking: The FFI does *not* guarantee that Haskell's
malloc(Bytes)/realloc(Bytes)/free is the same as C's malloc/realloc/free.
So you should not e.g. use C's free for something allocated via Haskell's
malloc.
Apart from that, it may help to remember the following "equations":
alloca = malloc + free (exception-safe!)
new = malloc + poke
with = alloca + poke
Depending on your needs, pooled allocation may an option, too:
http://haskell.org/ghc/docs/latest/html/libraries/base/Foreign.Marshal.Pool.html
In that case, all allocations are belong to a given pool and memory is
deallocated when the pool in question is. Furthermore:
withPool = newPool + freePool (exception-safe!)
Cheers,
S.
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