C Interface

C Interface

ccall((symbol, library) or function_pointer, ReturnType, (ArgumentType1, ...), ArgumentValue1, ...)

Call function in C-exported shared library, specified by (function name, library) tuple, where each component is a string or symbol.

Note that the argument type tuple must be a literal tuple, and not a tuple-valued variable or expression. Alternatively, ccall may also be used to call a function pointer, such as one returned by dlsym.

Each ArgumentValue to the ccall will be converted to the corresponding ArgumentType, by automatic insertion of calls to unsafe_convert(ArgumentType, cconvert(ArgumentType, ArgumentValue)). (See also the documentation for each of these functions for further details.) In most cases, this simply results in a call to convert(ArgumentType, ArgumentValue).

cglobal((symbol, library)[, type=Void])

Obtain a pointer to a global variable in a C-exported shared library, specified exactly as in ccall. Returns a Ptr{Type}, defaulting to Ptr{Void} if no Type argument is supplied. The values can be read or written by unsafe_load or unsafe_store!, respectively.

cfunction(function::Function, ReturnType::Type, (ArgumentTypes...))

Generate C-callable function pointer from Julia function. Type annotation of the return value in the callback function is a must for situations where Julia cannot infer the return type automatically.

For example:

function foo()
    # body

    retval::Float64
end

bar = cfunction(foo, Float64, ())

unsafe_convert(T, x)

Convert x to a value of type T

In cases where convert would need to take a Julia object and turn it into a Ptr, this function should be used to define and perform that conversion.

Be careful to ensure that a Julia reference to x exists as long as the result of this function will be used. Accordingly, the argument x to this function should never be an expression, only a variable name or field reference. For example, x=a.b.c is acceptable, but x=[a,b,c] is not.

The unsafe prefix on this function indicates that using the result of this function after the x argument to this function is no longer accessible to the program may cause undefined behavior, including program corruption or segfaults, at any later time.

cconvert(T, x)

Convert x to a value of type T, typically by calling convert(T,x)

In cases where x cannot be safely converted to T, unlike convert, cconvert may return an object of a type different from T, which however is suitable for unsafe_convert to handle.

Neither convert nor cconvert should take a Julia object and turn it into a Ptr.

unsafe_load(p::Ptr{T}[, i::Integer=1])

Load a value of type T from the address of the ith element (1-indexed) starting at p. This is equivalent to the C expression p[i-1].

The unsafe prefix on this function indicates that no validation is performed on the pointer p to ensure that it is valid. Incorrect usage may segfault your program or return garbage answers, in the same manner as C.

unsafe_store!(p::Ptr{T}, x[, i::Integer=1])

Store a value of type T to the address of the ith element (1-indexed) starting at p. This is equivalent to the C expression p[i-1] = x.

The unsafe prefix on this function indicates that no validation is performed on the pointer p to ensure that it is valid. Incorrect usage may corrupt or segfault your program, in the same manner as C.

unsafe_copy!(dest::Ptr{T}, src::Ptr{T}, N)

Copy N elements from a source pointer to a destination, with no checking. The size of an element is determined by the type of the pointers.

The unsafe prefix on this function indicates that no validation is performed on the pointers dest and src to ensure that they are valid. Incorrect usage may corrupt or segfault your program, in the same manner as C.

unsafe_copy!(dest::Array, do, src::Array, so, N)

Copy N elements from a source array to a destination, starting at offset so in the source and do in the destination (1-indexed).

The unsafe prefix on this function indicates that no validation is performed to ensure that N is inbounds on either array. Incorrect usage may corrupt or segfault your program, in the same manner as C.

copy!(dest, src)

Copy all elements from collection src to array dest. Returns dest.

copy!(dest, do, src, so, N)

Copy N elements from collection src starting at offset so, to array dest starting at offset do. Returns dest.

pointer(array[, index])

Get the native address of an array or string element. Be careful to ensure that a Julia reference to a exists as long as this pointer will be used. This function is “unsafe” like unsafe_convert.

Calling Ref(array[, index]) is generally preferable to this function.

unsafe_wrap(Array, pointer::Ptr{T}, dims, own=false)

Wrap a Julia Array object around the data at the address given by pointer, without making a copy. The pointer element type T determines the array element type. dims is either an integer (for a 1d array) or a tuple of the array dimensions. own optionally specifies whether Julia should take ownership of the memory, calling free on the pointer when the array is no longer referenced.

This function is labelled “unsafe” because it will crash if pointer is not a valid memory address to data of the requested length.

pointer_from_objref(object_instance)

Get the memory address of a Julia object as a Ptr. The existence of the resulting Ptr will not protect the object from garbage collection, so you must ensure that the object remains referenced for the whole time that the Ptr will be used.

unsafe_pointer_to_objref(p::Ptr)

Convert a Ptr to an object reference. Assumes the pointer refers to a valid heap-allocated Julia object. If this is not the case, undefined behavior results, hence this function is considered “unsafe” and should be used with care.

disable_sigint(f::Function)

Disable Ctrl-C handler during execution of a function on the current task, for calling external code that may call julia code that is not interrupt safe. Intended to be called using do block syntax as follows:

disable_sigint() do
    # interrupt-unsafe code
    ...
end

This is not needed on worker threads (Threads.threadid() != 1) since the InterruptException will only be delivered to the master thread. External functions that do not call julia code or julia runtime automatically disable sigint during their execution.

reenable_sigint(f::Function)

Re-enable Ctrl-C handler during execution of a function. Temporarily reverses the effect of disable_sigint.

systemerror(sysfunc, iftrue)

Raises a SystemError for errno with the descriptive string sysfunc if iftrue is true

Ptr{T}

A memory address referring to data of type T. However, there is no guarantee that the memory is actually valid, or that it actually represents data of the specified type.

Ref{T}

An object that safely references data of type T. This type is guaranteed to point to valid, Julia-allocated memory of the correct type. The underlying data is protected from freeing by the garbage collector as long as the Ref itself is referenced.

When passed as a ccall argument (either as a Ptr or Ref type), a Ref object will be converted to a native pointer to the data it references.

There is no invalid (NULL) Ref.

Cchar

Equivalent to the native char c-type.

Cuchar

Equivalent to the native unsigned char c-type (UInt8).

Cshort

Equivalent to the native signed short c-type (Int16).

Cushort

Equivalent to the native unsigned short c-type (UInt16).

Cint

Equivalent to the native signed int c-type (Int32).

Cuint

Equivalent to the native unsigned int c-type (UInt32).

Clong

Equivalent to the native signed long c-type.

Culong

Equivalent to the native unsigned long c-type.

Clonglong

Equivalent to the native signed long long c-type (Int64).

Culonglong

Equivalent to the native unsigned long long c-type (UInt64).

Cintmax_t

Equivalent to the native intmax_t c-type (Int64).

Cuintmax_t

Equivalent to the native uintmax_t c-type (UInt64).

Csize_t

Equivalent to the native size_t c-type (UInt).

Cssize_t

Equivalent to the native ssize_t c-type.

Cptrdiff_t

Equivalent to the native ptrdiff_t c-type (Int).

Cwchar_t

Equivalent to the native wchar_t c-type (Int32).

Cfloat

Equivalent to the native float c-type (Float32).

Cdouble

Equivalent to the native double c-type (Float64).