CtypesThe core ctypes module.
The main points of interest are the set of functions for describing C types (see Values representing C types) and the set of functions for accessing C values (see Values representing C values). The Foreign.foreign function uses C type descriptions to bind external C values.
type ('a, 'b) pointer = ('a, 'b) Ctypes_static.pointerThe type of pointer values. A value of type ('a, [`C]) pointer contains a C-compatible pointer, and a value of type ('a, [`OCaml]) pointer contains a pointer to a value that can be moved by OCaml runtime.
type 'a ptr = ('a, [ `C ]) pointerThe type of C-compatible pointer values. A value of type t ptr can be used to read and write values of type t at particular addresses.
type 'a ocaml = 'a Ctypes_static.ocamlThe type of pointer values pointing directly into OCaml values. Pointers of this type should never be captured by external code. In particular, functions accepting 'a ocaml pointers must not invoke any OCaml code.
type 'a carray = 'a Ctypes_static.carrayThe type of C array values. A value of type t carray can be used to read and write array objects in C-managed storage.
type 'a bigarray_class = 'a Ctypes_static.bigarray_classThe type of Bigarray classes. There are four instances, one for each of the Bigarray submodules.
val genarray :
< element : 'a
; layout : 'l
; ba_repr : 'b
; bigarray : ('a, 'b, 'l) Bigarray_compat.Genarray.t
; carray : 'a carray
; dims : int array >
bigarray_classThe class of Bigarray.Genarray.t values
val array1 :
< element : 'a
; layout : 'l
; ba_repr : 'b
; bigarray : ('a, 'b, 'l) Bigarray_compat.Array1.t
; carray : 'a carray
; dims : int >
bigarray_classThe class of Bigarray.Array1.t values
val array2 :
< element : 'a
; layout : 'l
; ba_repr : 'b
; bigarray : ('a, 'b, 'l) Bigarray_compat.Array2.t
; carray : 'a carray carray
; dims : int * int >
bigarray_classThe class of Bigarray.Array2.t values
val array3 :
< element : 'a
; layout : 'l
; ba_repr : 'b
; bigarray : ('a, 'b, 'l) Bigarray_compat.Array3.t
; carray : 'a carray carray carray
; dims : int * int * int >
bigarray_classThe class of Bigarray.Array3.t values
type ('a, 'kind) structured = ('a, 'kind) Ctypes_static.structuredThe base type of values representing C struct and union types. The 'kind parameter is a polymorphic variant type indicating whether the type represents a struct (`Struct) or a union (`Union).
type 'a structure = ('a, [ `Struct ]) structuredThe type of values representing C struct types.
type 'a union = ('a, [ `Union ]) structuredThe type of values representing C union types.
type ('a, 't) field = ('a, 't) Ctypes_static.fieldThe type of values representing C struct or union members (called "fields" here). A value of type (a, s) field represents a field of type a in a struct or union of type s.
type 'a abstract = 'a Ctypes_static.abstractThe type of abstract values. The purpose of the abstract type is to represent values whose type varies from platform to platform.
For example, the type pthread_t is a pointer on some platforms, an integer on other platforms, and a struct on a third set of platforms. One way to deal with this kind of situation is to have possibly-platform-specific code which interrogates the C type in some way to help determine an appropriate representation. Another way is to use abstract, leaving the representation opaque.
(Note, however, that although pthread_t is a convenient example, since the type used to implement it varies significantly across platforms, it's not actually a good match for abstract, since values of type pthread_t are passed and returned by value.)
include Ctypes_types.TYPE
with type 'a typ = 'a Ctypes_static.typ
and type ('a, 's) field := ('a, 's) fieldtype 'a typ = 'a Ctypes_static.typThe type of values representing C types. There are two types associated with each typ value: the C type used to store and pass values, and the corresponding OCaml type. The type parameter indicates the OCaml type, so a value of type t typ is used to read and write OCaml values of type t. There are various uses of typ values, including
Foreign.foreignptrval void : unit typValue representing the C void type. Void values appear in OCaml as the unit type, so using void in an argument or result type specification produces a function which accepts or returns unit.
Dereferencing a pointer to void is an error, as in C, and will raise IncompleteType.
The scalar types consist of the Arithmetic types and the Pointer types.
The arithmetic types consist of the signed and unsigned integer types (including character types) and the floating types. There are values representing both exact-width integer types (of 8, 16, 32 and 64 bits) and types whose size depend on the platform (signed and unsigned short, int, long, long long).
val char : char typValue representing the C type char.
val schar : int typValue representing the C type signed char.
val short : int typValue representing the C type (signed) short.
val int : int typValue representing the C type (signed) int.
val long : Signed.long typValue representing the C type (signed) long.
val llong : Signed.llong typValue representing the C type (signed) long long.
val nativeint : nativeint typValue representing the C type (signed) int.
val int8_t : int typValue representing an 8-bit signed integer C type.
val int16_t : int typValue representing a 16-bit signed integer C type.
val int32_t : int32 typValue representing a 32-bit signed integer C type.
val int64_t : int64 typValue representing a 64-bit signed integer C type.
val camlint : int typValue representing an integer type with the same storage requirements as an OCaml int.
val uchar : Unsigned.uchar typValue representing the C type unsigned char.
val bool : bool typValue representing the C type bool.
val uint8_t : Unsigned.uint8 typValue representing an 8-bit unsigned integer C type.
val uint16_t : Unsigned.uint16 typValue representing a 16-bit unsigned integer C type.
val uint32_t : Unsigned.uint32 typValue representing a 32-bit unsigned integer C type.
val uint64_t : Unsigned.uint64 typValue representing a 64-bit unsigned integer C type.
val size_t : Unsigned.size_t typValue representing the C type size_t, an alias for one of the unsigned integer types. The actual size and alignment requirements for size_t vary between platforms.
val ushort : Unsigned.ushort typValue representing the C type unsigned short.
val sint : Signed.sint typValue representing the C type int.
val uint : Unsigned.uint typValue representing the C type unsigned int.
val ulong : Unsigned.ulong typValue representing the C type unsigned long.
val ullong : Unsigned.ullong typValue representing the C type unsigned long long.
module Uintptr : Unsigned.Sval float : float typValue representing the C single-precision float type.
val double : float typValue representing the C type double.
val complexld : ComplexL.t typValue representing the C99 long-double-precision long double complex type.
val ptr : 'a typ -> 'a Ctypes_static.ptr typConstruct a pointer type from an existing type (called the reference type).
val ptr_opt : 'a typ -> 'a Ctypes_static.ptr option typConstruct a pointer type from an existing type (called the reference type). This behaves like ptr, except that null pointers appear in OCaml as None.
val string : string typA high-level representation of the string type.
On the C side this behaves like char *; on the OCaml side values read and written using string are simply native OCaml strings.
To avoid problems with the garbage collector, values passed using string are copied into immovable C-managed storage before being passed to C.
The string type representation is suitable for use in function argument types such as the following:
string @-> returning int
where the lifetime of the C-managed storage does not need to extend beyond the duration of the function call. However, it is not suitable for use in struct or union fields
field s "x" string
because it does not provide a way to manage the lifetime of the C-managed storage.
val string_opt : string option typA high-level representation of the string type. This behaves like string, except that null pointers appear in OCaml as None.
val ocaml_string : string Ctypes_static.ocaml typValue representing the directly mapped storage of an OCaml string.
val ocaml_bytes : bytes Ctypes_static.ocaml typValue representing the directly mapped storage of an OCaml byte array.
val array : int -> 'a typ -> 'a Ctypes_static.carray typConstruct a sized array type from a length and an existing type (called the element type).
val bigarray :
< element : 'a
; layout : Bigarray_compat.c_layout
; ba_repr : 'b
; dims : 'dims
; bigarray : 'bigarray
; carray : _ >
Ctypes_static.bigarray_class ->
'dims ->
('a, 'b) Bigarray_compat.kind ->
'bigarray typConstruct a sized C-layout bigarray type representation from a bigarray class, the dimensions, and the Bigarray_compat.kind.
val fortran_bigarray :
< element : 'a
; layout : Bigarray_compat.fortran_layout
; ba_repr : 'b
; dims : 'dims
; bigarray : 'bigarray
; carray : _ >
Ctypes_static.bigarray_class ->
'dims ->
('a, 'b) Bigarray_compat.kind ->
'bigarray typConstruct a sized Fortran-layout bigarray type representation from a bigarray class, the dimensions, and the Bigarray_compat.kind.
val typ_of_bigarray_kind : ('a, 'b) Bigarray_compat.kind -> 'a typtyp_of_bigarray_kind k is the type corresponding to the Bigarray kind k.
val structure : string -> 's Ctypes_static.structure typConstruct a new structure type. The type value returned is incomplete and can be updated using field until it is passed to seal, at which point the set of fields is fixed.
The type ('_s structure typ) of the expression returned by the call structure tag includes a weak type variable, which can be explicitly instantiated to ensure that the OCaml values representing different C structure types have incompatible types. Typical usage is as follows:
type tagname
let tagname : tagname structure typ = structure "tagname"
val union : string -> 's Ctypes_static.union typval field :
't typ ->
string ->
'a typ ->
('a, ('s, [< `Struct | `Union ]) Ctypes_static.structured as 't) fieldfield ty label ty' adds a field of type ty' with label label to the structure or union type ty and returns a field value that can be used to read and write the field in structure or union instances (e.g. using getf and setf).
Attempting to add a field to a union type that has been sealed with seal is an error, and will raise ModifyingSealedType.
val seal : (_, [< `Struct | `Union ]) Ctypes_static.structured typ -> unitseal t completes the struct or union type t so that no further fields can be added. Struct and union types must be sealed before they can be used in a way that involves their size or alignment; see the documentation for IncompleteType for further details.
val view :
?format_typ:((Format.formatter -> unit) -> Format.formatter -> unit) ->
?format:(Format.formatter -> 'b -> unit) ->
read:('a -> 'b) ->
write:('b -> 'a) ->
'a typ ->
'b typview ~read:r ~write:w t creates a C type representation t' which behaves like t except that values read using t' are subsequently transformed using the function r and values written using t' are first transformed using the function w.
For example, given suitable definitions of string_of_char_ptr and char_ptr_of_string, the type representation
view ~read:string_of_char_ptr ~write:char_ptr_of_string (ptr char)
can be used to pass OCaml strings directly to and from bound C functions, or to read and write string members in structs and arrays. (In fact, the string type representation is defined in exactly this way.)
The optional argument format_typ is used by the Ctypes.format_typ and string_of_typ functions to print the type at the top level and elsewhere. If format_typ is not supplied the printer for t is used instead.
The optional argument format is used by the Ctypes.format and string_of functions to print the values. If format_val is not supplied the printer for t is used instead.
typedef t name creates a C type representation t' which is equivalent to t except its name is printed as name.
This is useful when generating C stubs involving "anonymous" types, for example: typedef struct { int f } typedef_name;
val abstract :
name:string ->
size:int ->
alignment:int ->
'a Ctypes_static.abstract typCreate an abstract type specification from the size and alignment requirements for the type.
val lift_typ : 'a Ctypes_static.typ -> 'a typlift_typ t turns a concrete type representation into an abstract type representation.
For example, retrieving struct layout from C involves working with an abstract representation of types which do not support operations such as sizeof. The lift_typ function makes it possible to use concrete type representations wherever such abstract type representations are needed.
Abstract interface to C function type descriptions
type 'a fn = 'a Ctypes_static.fnThe type of values representing C function types. A value of type t fn can be used to bind to C functions and to describe type of OCaml functions passed to C.
Construct a function type from a type and an existing function type. This corresponds to prepending a parameter to a C function parameter list. For example,
int @-> ptr void @-> returning float
describes a function type that accepts two arguments -- an integer and a pointer to void -- and returns a float.
type 'a static_funptr = 'a Ctypes_static.static_funptrFunction pointer types
The type of values representing C function pointer types.
val static_funptr : 'a fn -> 'a Ctypes_static.static_funptr typConstruct a function pointer type from an existing function type (called the reference type).
const t const-qualifies the type t. At present the only effect is that the type is marked 'const' in generated code.
volatile t volatile-qualifies the type t. At present the only effect is that the type is marked 'volatile' in generated code.
val sizeof : 'a typ -> intsizeof t computes the size in bytes of the type t. The exception IncompleteType is raised if t is incomplete.
val alignment : 'a typ -> intalignment t computes the alignment requirements of the type t. The exception IncompleteType is raised if t is incomplete.
val format_typ : ?name:string -> Format.formatter -> 'a typ -> unitPretty-print a C representation of the type to the specified formatter.
val format_fn : ?name:string -> Format.formatter -> 'a fn -> unitPretty-print a C representation of the function type to the specified formatter.
val string_of_typ : ?name:string -> 'a typ -> stringReturn a C representation of the type.
val string_of_fn : ?name:string -> 'a fn -> stringReturn a C representation of the function type.
val format : 'a typ -> Format.formatter -> 'a -> unitPretty-print a representation of the C value to the specified formatter.
val string_of : 'a typ -> 'a -> stringReturn a string representation of the C value.
val null : unit ptrA null pointer.
val (!@) : 'a ptr -> 'a!@ p dereferences the pointer p. If the reference type is a scalar type then dereferencing constructs a new value. If the reference type is an aggregate type then dereferencing returns a value that references the memory pointed to by p.
val (<-@) : 'a ptr -> 'a -> unitp <-@ v writes the value v to the address p.
If p is a pointer to an array element then p +@ n computes the address of the nth next element.
If p is a pointer to an array element then p -@ n computes the address of the nth previous element.
ptr_diff p q computes q - p. As in C, both p and q must point into the same array, and the result value is the difference of the subscripts of the two array elements.
allocate t v allocates a fresh value of type t, initialises it with v and returns its address. The argument ?finalise, if present, will be called just before the memory is freed. The value will be automatically freed after no references to the pointer remain within the calling OCaml program.
allocate_n t ~count:n allocates a fresh array with element type t and length n, and returns its address. The argument ?finalise, if present, will be called just before the memory is freed. The array will be automatically freed after no references to the pointer remain within the calling OCaml program. The memory is allocated with libc's calloc and is guaranteed to be zero-filled.
If p and q are pointers to elements i and j of the same array then ptr_compare p q compares the indexes of the elements. The result is negative if i is less than j, positive if i is greater than j, and zero if i and j are equal.
val is_null : 'a ptr -> boolis_null p is true when p is a null pointer.
val ptr_of_raw_address : nativeint -> unit ptrConvert the numeric representation of an address to a pointer
val funptr_of_raw_address :
nativeint ->
(unit -> unit) Ctypes_static.static_funptrConvert the numeric representation of an address to a function pointer
val raw_address_of_ptr : unit ptr -> nativeintraw_address_of_ptr p returns the numeric representation of p.
Note that the return value remains valid only as long as the pointed-to object is alive. If p is a managed object (e.g. a value returned by make) then unless the caller retains a reference to p, the object may be collected, invalidating the returned address.
val string_from_ptr : char ptr -> length:int -> stringstring_from_ptr p ~length creates a string initialized with the length characters at address p.
Raise Invalid_argument "Ctypes.string_from_ptr" if length is negative.
val ocaml_string_start : string -> string ocamlocaml_string_start s allows to pass a pointer to the contents of an OCaml string directly to a C function.
val ocaml_bytes_start : bytes -> bytes ocamlocaml_bytes_start s allows to pass a pointer to the contents of an OCaml byte array directly to a C function.
module CArray : sig ... endOperations on C arrays.
val bigarray_start :
< element : 'a
; layout : 'l
; ba_repr : _
; bigarray : 'b
; carray : _
; dims : _ >
bigarray_class ->
'b ->
'a ptrReturn the address of the first element of the given Bigarray value.
val bigarray_of_ptr :
< element : 'a
; layout : Bigarray_compat.c_layout
; ba_repr : 'f
; bigarray : 'b
; carray : _
; dims : 'i >
bigarray_class ->
'i ->
('a, 'f) Bigarray_compat.kind ->
'a ptr ->
'bbigarray_of_ptr c dims k p converts the C pointer p to a C-layout bigarray value. No copy is made; the bigarray references the memory pointed to by p.
val fortran_bigarray_of_ptr :
< element : 'a
; layout : Bigarray_compat.fortran_layout
; ba_repr : 'f
; bigarray : 'b
; carray : _
; dims : 'i >
bigarray_class ->
'i ->
('a, 'f) Bigarray_compat.kind ->
'a ptr ->
'bfortran_bigarray_of_ptr c dims k p converts the C pointer p to a Fortran-layout bigarray value. No copy is made; the bigarray references the memory pointed to by p.
val array_of_bigarray :
< element : _
; layout : Bigarray_compat.c_layout
; ba_repr : _
; bigarray : 'b
; carray : 'c
; dims : _ >
bigarray_class ->
'b ->
'carray_of_bigarray c b converts the bigarray value b to a value of type CArray.t. No copy is made; the result occupies the same memory as b.
Convert a Bigarray value to a C array.
val bigarray_of_array :
< element : 'a
; layout : Bigarray_compat.c_layout
; ba_repr : 'f
; bigarray : 'b
; carray : 'c carray
; dims : 'i >
bigarray_class ->
('a, 'f) Bigarray_compat.kind ->
'c carray ->
'bbigarray_of_array c k a converts the CArray.t value a to a C-layout bigarray value. No copy is made; the result occupies the same memory as a.
val make : ?finalise:('s -> unit) -> (_, _) structured as 's typ -> 'sAllocate a fresh, uninitialised structure or union value. The argument ?finalise, if present, will be called just before the underlying memory is freed.
val setf : (_, _) structured as 's -> ('a, 's) field -> 'a -> unitsetf s f v overwrites the value of the field f in the structure or union s with v.
val getf : (_, _) structured as 's -> ('a, 's) field -> 'agetf s f retrieves the value of the field f in the structure or union s. The semantics for non-scalar types are non-copying, as for (!@).
val (@.) : (_, _) structured as 's -> ('a, 's) field -> 'a ptrs @. f computes the address of the field f in the structure or union value s.
val (|->) : (_, _) structured as 's ptr -> ('a, 's) field -> 'a ptrp |-> f computes the address of the field f in the structure or union value pointed to by p.
offsetof f returns the offset, in bytes, of the field f from the beginning of the associated struct type.
val field_name : (_, _) field -> stringfield_name f returns the name of the field f.
val addr : (_, _) structured as 's -> 's ptraddr s returns the address of the structure or union s.
coerce t1 t2 returns a coercion function between the types represented by t1 and t2. If t1 cannot be coerced to t2, coerce raises Uncoercible.
The following coercions are currently supported:
voidview and another type t (in either direction) if there is a coercion between the representation type underlying the view and t.t1 is coercible to t2 and t2 is coercible to t3, then t1 is directly coercible to t3.The set of supported coercions is subject to change. Future versions of ctypes may both add new types of coercion and restrict the existing coercions.
coerce_fn f1 f2 returns a coercion function between the function types represented by f1 and f2. If f1 cannot be coerced to f2, coerce_fn raises Uncoercible.
A function type f1 may be coerced to another function type f2 if all of the following hold:
f1 and f2 have the same arityf2 may be coerced to the corresponding argument of f1f1 may be coerced to the return type of f2The set of supported coercions is subject to change. Future versions of ctypes may both add new types of coercion and restrict the existing coercions.
module type FOREIGN = sig ... endmodule type TYPE = sig ... endForeign types binding interface.
module Root : sig ... endAn attempt was made to use a feature not currently supported by ctypes. In practice this refers to attempts to use an union, array or abstract type as an argument or return type of a function.
An attempt was made to modify a sealed struct or union type description.
An attempt was made to compute the size or alignment of an incomplete type.
The incomplete types are struct and union types that have not been sealed, and the void type.
It is not permitted to compute the size or alignment requirements of an incomplete type, to use it as a struct or union member, to read or write a value of the type through a pointer or to use it as the referenced type in pointer arithmetic. Additionally, incomplete struct and union types cannot be used as argument or return types.
exception Uncoercible of uncoercible_infoAn attempt was made to coerce between uncoercible types.