Safe Haskell	Safe
Language	Haskell2010

Foreign.Ptr

Contents

Data pointers
Function pointers
Integral types with lossless conversion to and from pointers

Description

The module Foreign.Ptr provides typed pointers to foreign entities. We distinguish two kinds of pointers: pointers to data and pointers to functions. It is understood that these two kinds of pointers may be represented differently as they may be references to data and text segments, respectively.

Synopsis

data Ptr a
nullPtr :: Ptr a
castPtr :: Ptr a -> Ptr b
plusPtr :: Ptr a -> Int -> Ptr b
alignPtr :: Ptr a -> Int -> Ptr a
minusPtr :: Ptr a -> Ptr b -> Int
data FunPtr a
nullFunPtr :: FunPtr a
castFunPtr :: FunPtr a -> FunPtr b
castFunPtrToPtr :: FunPtr a -> Ptr b
castPtrToFunPtr :: Ptr a -> FunPtr b
freeHaskellFunPtr :: FunPtr a -> IO ()
data IntPtr
ptrToIntPtr :: Ptr a -> IntPtr
intPtrToPtr :: IntPtr -> Ptr a
data WordPtr
ptrToWordPtr :: Ptr a -> WordPtr
wordPtrToPtr :: WordPtr -> Ptr a

Data pointers

data Ptr a #

A value of type Ptr a represents a pointer to an object, or an array of objects, which may be marshalled to or from Haskell values of type a.

The type a will often be an instance of class Storable which provides the marshalling operations. However this is not essential, and you can provide your own operations to access the pointer. For example you might write small foreign functions to get or set the fields of a C struct.

Instances

Generic1 (URec (Ptr ()) :: k -> Type)
Instance details Defined in GHC.Generics Associated Types type Rep1 (URec (Ptr ())) :: k -> Type # Methods from1 :: URec (Ptr ()) a -> Rep1 (URec (Ptr ())) a # to1 :: Rep1 (URec (Ptr ())) a -> URec (Ptr ()) a #
Eq (Ptr a)	Since: base-2.1
Instance details Defined in GHC.Ptr Methods (==) :: Ptr a -> Ptr a -> Bool # (/=) :: Ptr a -> Ptr a -> Bool #
Ord (Ptr a)	Since: base-2.1
Instance details Defined in GHC.Ptr Methods compare :: Ptr a -> Ptr a -> Ordering # (<) :: Ptr a -> Ptr a -> Bool # (<=) :: Ptr a -> Ptr a -> Bool # (>) :: Ptr a -> Ptr a -> Bool # (>=) :: Ptr a -> Ptr a -> Bool # max :: Ptr a -> Ptr a -> Ptr a # min :: Ptr a -> Ptr a -> Ptr a #
Show (Ptr a)	Since: base-2.1
Instance details Defined in GHC.Ptr Methods showsPrec :: Int -> Ptr a -> ShowS # show :: Ptr a -> String # showList :: [Ptr a] -> ShowS #
Storable (Ptr a)	Since: base-2.1
Instance details Defined in Foreign.Storable Methods sizeOf :: Ptr a -> Int # alignment :: Ptr a -> Int # peekElemOff :: Ptr (Ptr a) -> Int -> IO (Ptr a) # pokeElemOff :: Ptr (Ptr a) -> Int -> Ptr a -> IO () # peekByteOff :: Ptr b -> Int -> IO (Ptr a) # pokeByteOff :: Ptr b -> Int -> Ptr a -> IO () # peek :: Ptr (Ptr a) -> IO (Ptr a) # poke :: Ptr (Ptr a) -> Ptr a -> IO () #
Functor (URec (Ptr ()) :: Type -> Type)	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods fmap :: (a -> b) -> URec (Ptr ()) a -> URec (Ptr ()) b # (<$) :: a -> URec (Ptr ()) b -> URec (Ptr ()) a #
Foldable (URec (Ptr ()) :: Type -> Type)	Since: base-4.9.0.0
Instance details Defined in Data.Foldable Methods fold :: Monoid m => URec (Ptr ()) m -> m # foldMap :: Monoid m => (a -> m) -> URec (Ptr ()) a -> m # foldr :: (a -> b -> b) -> b -> URec (Ptr ()) a -> b # foldr' :: (a -> b -> b) -> b -> URec (Ptr ()) a -> b # foldl :: (b -> a -> b) -> b -> URec (Ptr ()) a -> b # foldl' :: (b -> a -> b) -> b -> URec (Ptr ()) a -> b # foldr1 :: (a -> a -> a) -> URec (Ptr ()) a -> a # foldl1 :: (a -> a -> a) -> URec (Ptr ()) a -> a # toList :: URec (Ptr ()) a -> [a] # null :: URec (Ptr ()) a -> Bool # length :: URec (Ptr ()) a -> Int # elem :: Eq a => a -> URec (Ptr ()) a -> Bool # maximum :: Ord a => URec (Ptr ()) a -> a # minimum :: Ord a => URec (Ptr ()) a -> a # sum :: Num a => URec (Ptr ()) a -> a # product :: Num a => URec (Ptr ()) a -> a #
Traversable (URec (Ptr ()) :: Type -> Type)	Since: base-4.9.0.0
Instance details Defined in Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> URec (Ptr ()) a -> f (URec (Ptr ()) b) # sequenceA :: Applicative f => URec (Ptr ()) (f a) -> f (URec (Ptr ()) a) # mapM :: Monad m => (a -> m b) -> URec (Ptr ()) a -> m (URec (Ptr ()) b) # sequence :: Monad m => URec (Ptr ()) (m a) -> m (URec (Ptr ()) a) #
Eq (URec (Ptr ()) p)	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods (==) :: URec (Ptr ()) p -> URec (Ptr ()) p -> Bool # (/=) :: URec (Ptr ()) p -> URec (Ptr ()) p -> Bool #
Ord (URec (Ptr ()) p)	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods compare :: URec (Ptr ()) p -> URec (Ptr ()) p -> Ordering # (<) :: URec (Ptr ()) p -> URec (Ptr ()) p -> Bool # (<=) :: URec (Ptr ()) p -> URec (Ptr ()) p -> Bool # (>) :: URec (Ptr ()) p -> URec (Ptr ()) p -> Bool # (>=) :: URec (Ptr ()) p -> URec (Ptr ()) p -> Bool # max :: URec (Ptr ()) p -> URec (Ptr ()) p -> URec (Ptr ()) p # min :: URec (Ptr ()) p -> URec (Ptr ()) p -> URec (Ptr ()) p #
Generic (URec (Ptr ()) p)
Instance details Defined in GHC.Generics Associated Types type Rep (URec (Ptr ()) p) :: Type -> Type # Methods from :: URec (Ptr ()) p -> Rep (URec (Ptr ()) p) x # to :: Rep (URec (Ptr ()) p) x -> URec (Ptr ()) p #
data URec (Ptr ()) (p :: k)	Used for marking occurrences of `Addr#` Since: base-4.9.0.0
Instance details Defined in GHC.Generics data URec (Ptr ()) (p :: k) = UAddr { uAddr# :: Addr# }
type Rep1 (URec (Ptr ()) :: k -> Type)	Since: base-4.9.0.0
Instance details Defined in GHC.Generics type Rep1 (URec (Ptr ()) :: k -> Type) = D1 (MetaData "URec" "GHC.Generics" "base" False) (C1 (MetaCons "UAddr" PrefixI True) (S1 (MetaSel (Just "uAddr#") NoSourceUnpackedness NoSourceStrictness DecidedLazy) (UAddr :: k -> Type)))
type Rep (URec (Ptr ()) p)	Since: base-4.9.0.0
Instance details Defined in GHC.Generics type Rep (URec (Ptr ()) p) = D1 (MetaData "URec" "GHC.Generics" "base" False) (C1 (MetaCons "UAddr" PrefixI True) (S1 (MetaSel (Just "uAddr#") NoSourceUnpackedness NoSourceStrictness DecidedLazy) (UAddr :: Type -> Type)))

nullPtr :: Ptr a #

The constant nullPtr contains a distinguished value of Ptr that is not associated with a valid memory location.

castPtr :: Ptr a -> Ptr b #

The castPtr function casts a pointer from one type to another.

plusPtr :: Ptr a -> Int -> Ptr b #

Advances the given address by the given offset in bytes.

alignPtr :: Ptr a -> Int -> Ptr a #

Given an arbitrary address and an alignment constraint, alignPtr yields the next higher address that fulfills the alignment constraint. An alignment constraint x is fulfilled by any address divisible by x. This operation is idempotent.

minusPtr :: Ptr a -> Ptr b -> Int #

Computes the offset required to get from the second to the first argument. We have

p2 == p1 `plusPtr` (p2 `minusPtr` p1)

Function pointers

data FunPtr a #

A value of type FunPtr a is a pointer to a function callable from foreign code. The type a will normally be a foreign type, a function type with zero or more arguments where

the argument types are marshallable foreign types, i.e. Char, Int, Double, Float, Bool, Int8, Int16, Int32, Int64, Word8, Word16, Word32, Word64, Ptr a, FunPtr a, StablePtr a or a renaming of any of these using newtype.
the return type is either a marshallable foreign type or has the form IO t where t is a marshallable foreign type or ().

A value of type FunPtr a may be a pointer to a foreign function, either returned by another foreign function or imported with a a static address import like

foreign import ccall "stdlib.h &free"
  p_free :: FunPtr (Ptr a -> IO ())

or a pointer to a Haskell function created using a wrapper stub declared to produce a FunPtr of the correct type. For example:

type Compare = Int -> Int -> Bool
foreign import ccall "wrapper"
  mkCompare :: Compare -> IO (FunPtr Compare)

Calls to wrapper stubs like mkCompare allocate storage, which should be released with freeHaskellFunPtr when no longer required.

To convert FunPtr values to corresponding Haskell functions, one can define a dynamic stub for the specific foreign type, e.g.

type IntFunction = CInt -> IO ()
foreign import ccall "dynamic"
  mkFun :: FunPtr IntFunction -> IntFunction

Instances

Eq (FunPtr a)
Instance details Defined in GHC.Ptr Methods (==) :: FunPtr a -> FunPtr a -> Bool # (/=) :: FunPtr a -> FunPtr a -> Bool #
Ord (FunPtr a)
Instance details Defined in GHC.Ptr Methods compare :: FunPtr a -> FunPtr a -> Ordering # (<) :: FunPtr a -> FunPtr a -> Bool # (<=) :: FunPtr a -> FunPtr a -> Bool # (>) :: FunPtr a -> FunPtr a -> Bool # (>=) :: FunPtr a -> FunPtr a -> Bool # max :: FunPtr a -> FunPtr a -> FunPtr a # min :: FunPtr a -> FunPtr a -> FunPtr a #
Show (FunPtr a)	Since: base-2.1
Instance details Defined in GHC.Ptr Methods showsPrec :: Int -> FunPtr a -> ShowS # show :: FunPtr a -> String # showList :: [FunPtr a] -> ShowS #
Storable (FunPtr a)	Since: base-2.1
Instance details Defined in Foreign.Storable Methods sizeOf :: FunPtr a -> Int # alignment :: FunPtr a -> Int # peekElemOff :: Ptr (FunPtr a) -> Int -> IO (FunPtr a) # pokeElemOff :: Ptr (FunPtr a) -> Int -> FunPtr a -> IO () # peekByteOff :: Ptr b -> Int -> IO (FunPtr a) # pokeByteOff :: Ptr b -> Int -> FunPtr a -> IO () # peek :: Ptr (FunPtr a) -> IO (FunPtr a) # poke :: Ptr (FunPtr a) -> FunPtr a -> IO () #

nullFunPtr :: FunPtr a #

The constant nullFunPtr contains a distinguished value of FunPtr that is not associated with a valid memory location.

castFunPtr :: FunPtr a -> FunPtr b #

Casts a FunPtr to a FunPtr of a different type.

castFunPtrToPtr :: FunPtr a -> Ptr b #

Casts a FunPtr to a Ptr.

Note: this is valid only on architectures where data and function pointers range over the same set of addresses, and should only be used for bindings to external libraries whose interface already relies on this assumption.

castPtrToFunPtr :: Ptr a -> FunPtr b #

Casts a Ptr to a FunPtr.

Note: this is valid only on architectures where data and function pointers range over the same set of addresses, and should only be used for bindings to external libraries whose interface already relies on this assumption.

freeHaskellFunPtr :: FunPtr a -> IO () #

Release the storage associated with the given FunPtr, which must have been obtained from a wrapper stub. This should be called whenever the return value from a foreign import wrapper function is no longer required; otherwise, the storage it uses will leak.

Integral types with lossless conversion to and from pointers

data IntPtr #

A signed integral type that can be losslessly converted to and from Ptr. This type is also compatible with the C99 type intptr_t, and can be marshalled to and from that type safely.

Instances

Bounded IntPtr
Instance details Defined in Foreign.Ptr Methods minBound :: IntPtr # maxBound :: IntPtr #
Enum IntPtr
Instance details Defined in Foreign.Ptr Methods succ :: IntPtr -> IntPtr # pred :: IntPtr -> IntPtr # toEnum :: Int -> IntPtr # fromEnum :: IntPtr -> Int # enumFrom :: IntPtr -> [IntPtr] # enumFromThen :: IntPtr -> IntPtr -> [IntPtr] # enumFromTo :: IntPtr -> IntPtr -> [IntPtr] # enumFromThenTo :: IntPtr -> IntPtr -> IntPtr -> [IntPtr] #
Eq IntPtr
Instance details Defined in Foreign.Ptr Methods (==) :: IntPtr -> IntPtr -> Bool # (/=) :: IntPtr -> IntPtr -> Bool #
Integral IntPtr
Instance details Defined in Foreign.Ptr Methods quot :: IntPtr -> IntPtr -> IntPtr # rem :: IntPtr -> IntPtr -> IntPtr # div :: IntPtr -> IntPtr -> IntPtr # mod :: IntPtr -> IntPtr -> IntPtr # quotRem :: IntPtr -> IntPtr -> (IntPtr, IntPtr) # divMod :: IntPtr -> IntPtr -> (IntPtr, IntPtr) # toInteger :: IntPtr -> Integer #
Num IntPtr
Instance details Defined in Foreign.Ptr Methods (+) :: IntPtr -> IntPtr -> IntPtr # (-) :: IntPtr -> IntPtr -> IntPtr # (*) :: IntPtr -> IntPtr -> IntPtr # negate :: IntPtr -> IntPtr # abs :: IntPtr -> IntPtr # signum :: IntPtr -> IntPtr # fromInteger :: Integer -> IntPtr #
Ord IntPtr
Instance details Defined in Foreign.Ptr Methods compare :: IntPtr -> IntPtr -> Ordering # (<) :: IntPtr -> IntPtr -> Bool # (<=) :: IntPtr -> IntPtr -> Bool # (>) :: IntPtr -> IntPtr -> Bool # (>=) :: IntPtr -> IntPtr -> Bool # max :: IntPtr -> IntPtr -> IntPtr # min :: IntPtr -> IntPtr -> IntPtr #
Read IntPtr
Instance details Defined in Foreign.Ptr Methods readsPrec :: Int -> ReadS IntPtr # readList :: ReadS [IntPtr] # readPrec :: ReadPrec IntPtr # readListPrec :: ReadPrec [IntPtr] #
Real IntPtr
Instance details Defined in Foreign.Ptr Methods toRational :: IntPtr -> Rational #
Show IntPtr
Instance details Defined in Foreign.Ptr Methods showsPrec :: Int -> IntPtr -> ShowS # show :: IntPtr -> String # showList :: [IntPtr] -> ShowS #
Storable IntPtr
Instance details Defined in Foreign.Ptr Methods sizeOf :: IntPtr -> Int # alignment :: IntPtr -> Int # peekElemOff :: Ptr IntPtr -> Int -> IO IntPtr # pokeElemOff :: Ptr IntPtr -> Int -> IntPtr -> IO () # peekByteOff :: Ptr b -> Int -> IO IntPtr # pokeByteOff :: Ptr b -> Int -> IntPtr -> IO () # peek :: Ptr IntPtr -> IO IntPtr # poke :: Ptr IntPtr -> IntPtr -> IO () #
Bits IntPtr
Instance details Defined in Foreign.Ptr Methods (.&.) :: IntPtr -> IntPtr -> IntPtr # (.\|.) :: IntPtr -> IntPtr -> IntPtr # xor :: IntPtr -> IntPtr -> IntPtr # complement :: IntPtr -> IntPtr # shift :: IntPtr -> Int -> IntPtr # rotate :: IntPtr -> Int -> IntPtr # zeroBits :: IntPtr # bit :: Int -> IntPtr # setBit :: IntPtr -> Int -> IntPtr # clearBit :: IntPtr -> Int -> IntPtr # complementBit :: IntPtr -> Int -> IntPtr # testBit :: IntPtr -> Int -> Bool # bitSizeMaybe :: IntPtr -> Maybe Int # bitSize :: IntPtr -> Int # isSigned :: IntPtr -> Bool # shiftL :: IntPtr -> Int -> IntPtr # unsafeShiftL :: IntPtr -> Int -> IntPtr # shiftR :: IntPtr -> Int -> IntPtr # unsafeShiftR :: IntPtr -> Int -> IntPtr # rotateL :: IntPtr -> Int -> IntPtr # rotateR :: IntPtr -> Int -> IntPtr # popCount :: IntPtr -> Int #
FiniteBits IntPtr
Instance details Defined in Foreign.Ptr Methods finiteBitSize :: IntPtr -> Int # countLeadingZeros :: IntPtr -> Int # countTrailingZeros :: IntPtr -> Int #

ptrToIntPtr :: Ptr a -> IntPtr #

casts a Ptr to an IntPtr

intPtrToPtr :: IntPtr -> Ptr a #

casts an IntPtr to a Ptr

data WordPtr #

An unsigned integral type that can be losslessly converted to and from Ptr. This type is also compatible with the C99 type uintptr_t, and can be marshalled to and from that type safely.

Instances

Bounded WordPtr
Instance details Defined in Foreign.Ptr Methods minBound :: WordPtr # maxBound :: WordPtr #
Enum WordPtr
Instance details Defined in Foreign.Ptr Methods succ :: WordPtr -> WordPtr # pred :: WordPtr -> WordPtr # toEnum :: Int -> WordPtr # fromEnum :: WordPtr -> Int # enumFrom :: WordPtr -> [WordPtr] # enumFromThen :: WordPtr -> WordPtr -> [WordPtr] # enumFromTo :: WordPtr -> WordPtr -> [WordPtr] # enumFromThenTo :: WordPtr -> WordPtr -> WordPtr -> [WordPtr] #
Eq WordPtr
Instance details Defined in Foreign.Ptr Methods (==) :: WordPtr -> WordPtr -> Bool # (/=) :: WordPtr -> WordPtr -> Bool #
Integral WordPtr
Instance details Defined in Foreign.Ptr Methods quot :: WordPtr -> WordPtr -> WordPtr # rem :: WordPtr -> WordPtr -> WordPtr # div :: WordPtr -> WordPtr -> WordPtr # mod :: WordPtr -> WordPtr -> WordPtr # quotRem :: WordPtr -> WordPtr -> (WordPtr, WordPtr) # divMod :: WordPtr -> WordPtr -> (WordPtr, WordPtr) # toInteger :: WordPtr -> Integer #
Num WordPtr
Instance details Defined in Foreign.Ptr Methods (+) :: WordPtr -> WordPtr -> WordPtr # (-) :: WordPtr -> WordPtr -> WordPtr # (*) :: WordPtr -> WordPtr -> WordPtr # negate :: WordPtr -> WordPtr # abs :: WordPtr -> WordPtr # signum :: WordPtr -> WordPtr # fromInteger :: Integer -> WordPtr #
Ord WordPtr
Instance details Defined in Foreign.Ptr Methods compare :: WordPtr -> WordPtr -> Ordering # (<) :: WordPtr -> WordPtr -> Bool # (<=) :: WordPtr -> WordPtr -> Bool # (>) :: WordPtr -> WordPtr -> Bool # (>=) :: WordPtr -> WordPtr -> Bool # max :: WordPtr -> WordPtr -> WordPtr # min :: WordPtr -> WordPtr -> WordPtr #
Read WordPtr
Instance details Defined in Foreign.Ptr Methods readsPrec :: Int -> ReadS WordPtr # readList :: ReadS [WordPtr] # readPrec :: ReadPrec WordPtr # readListPrec :: ReadPrec [WordPtr] #
Real WordPtr
Instance details Defined in Foreign.Ptr Methods toRational :: WordPtr -> Rational #
Show WordPtr
Instance details Defined in Foreign.Ptr Methods showsPrec :: Int -> WordPtr -> ShowS # show :: WordPtr -> String # showList :: [WordPtr] -> ShowS #
Storable WordPtr
Instance details Defined in Foreign.Ptr Methods sizeOf :: WordPtr -> Int # alignment :: WordPtr -> Int # peekElemOff :: Ptr WordPtr -> Int -> IO WordPtr # pokeElemOff :: Ptr WordPtr -> Int -> WordPtr -> IO () # peekByteOff :: Ptr b -> Int -> IO WordPtr # pokeByteOff :: Ptr b -> Int -> WordPtr -> IO () # peek :: Ptr WordPtr -> IO WordPtr # poke :: Ptr WordPtr -> WordPtr -> IO () #
Bits WordPtr
Instance details Defined in Foreign.Ptr Methods (.&.) :: WordPtr -> WordPtr -> WordPtr # (.\|.) :: WordPtr -> WordPtr -> WordPtr # xor :: WordPtr -> WordPtr -> WordPtr # complement :: WordPtr -> WordPtr # shift :: WordPtr -> Int -> WordPtr # rotate :: WordPtr -> Int -> WordPtr # zeroBits :: WordPtr # bit :: Int -> WordPtr # setBit :: WordPtr -> Int -> WordPtr # clearBit :: WordPtr -> Int -> WordPtr # complementBit :: WordPtr -> Int -> WordPtr # testBit :: WordPtr -> Int -> Bool # bitSizeMaybe :: WordPtr -> Maybe Int # bitSize :: WordPtr -> Int # isSigned :: WordPtr -> Bool # shiftL :: WordPtr -> Int -> WordPtr # unsafeShiftL :: WordPtr -> Int -> WordPtr # shiftR :: WordPtr -> Int -> WordPtr # unsafeShiftR :: WordPtr -> Int -> WordPtr # rotateL :: WordPtr -> Int -> WordPtr # rotateR :: WordPtr -> Int -> WordPtr # popCount :: WordPtr -> Int #
FiniteBits WordPtr
Instance details Defined in Foreign.Ptr Methods finiteBitSize :: WordPtr -> Int # countLeadingZeros :: WordPtr -> Int # countTrailingZeros :: WordPtr -> Int #

ptrToWordPtr :: Ptr a -> WordPtr #

casts a Ptr to a WordPtr

wordPtrToPtr :: WordPtr -> Ptr a #

casts a WordPtr to a Ptr