haskell2010-1.1.2.0: Compatibility with Haskell 2010

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 :: * -> * Source

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

Eq (Ptr a) |
Ord (Ptr a) |
Show (Ptr a) |
Storable (Ptr a) |

nullPtr :: Ptr a Source

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

castPtr :: Ptr a -> Ptr b Source

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

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

Advances the given address by the given offset in bytes.

alignPtr :: Ptr a -> Int -> Ptr a Source

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 Source

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 :: * -> * Source

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) |
Ord (FunPtr a) |
Show (FunPtr a) |
Storable (FunPtr a) |

nullFunPtr :: FunPtr a Source

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

castFunPtr :: FunPtr a -> FunPtr b Source

Casts a `FunPtr` to a `FunPtr` of a different type.

castFunPtrToPtr :: FunPtr a -> Ptr b Source

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 Source

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 () Source

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 :: * Source

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 |
Enum IntPtr |
Eq IntPtr |
Integral IntPtr |
Num IntPtr |
Ord IntPtr |
Read IntPtr |
Real IntPtr |
Show IntPtr |
Storable IntPtr |
Bits IntPtr |
FiniteBits IntPtr |
Typeable * IntPtr |

ptrToIntPtr :: Ptr a -> IntPtr Source

casts a `Ptr` to an `IntPtr`

intPtrToPtr :: IntPtr -> Ptr a Source

casts an `IntPtr` to a `Ptr`

data WordPtr :: * Source

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 |
Enum WordPtr |
Eq WordPtr |
Integral WordPtr |
Num WordPtr |
Ord WordPtr |
Read WordPtr |
Real WordPtr |
Show WordPtr |
Storable WordPtr |
Bits WordPtr |
FiniteBits WordPtr |
Typeable * WordPtr |

ptrToWordPtr :: Ptr a -> WordPtr Source

casts a `Ptr` to a `WordPtr`

wordPtrToPtr :: WordPtr -> Ptr a Source

casts a `WordPtr` to a `Ptr`