C Interface

    Call a function in a C-exported shared library, specified by the tuple (function_name, library), where each component is either a string or symbol. Instead of specifying a library, one can also use a function_name symbol or string, which is resolved in the current process. Alternatively, ccall may also be used to call a function pointer function_pointer, such as one returned by dlsym.

    Note that the argument type tuple must be a literal tuple, and not a tuple-valued variable or expression.

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

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    — Function.

    1. cglobal((symbol, library) [, type=Cvoid])

    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{Cvoid} if no Type argument is supplied. The values can be read or written by or unsafe_store!, respectively.

    Base.@cfunction — Macro.

    1. @cfunction(callable, ReturnType, (ArgumentTypes...,)) -> Ptr{Cvoid}
    2. @cfunction($callable, ReturnType, (ArgumentTypes...,)) -> CFunction

    Generate a C-callable function pointer from the Julia function callable for the given type signature. To pass the return value to a ccall, use the argument type Ptr{Cvoid} in the signature.

    Note that the argument type tuple must be a literal tuple, and not a tuple-valued variable or expression (although it can include a splat expression). And that these arguments will be evaluated in global scope during compile-time (not deferred until runtime). Adding a ‘$’ in front of the function argument changes this to instead create a runtime closure over the local variable callable.

    See .

    Examples

    1. julia> function foo(x::Int, y::Int)
    2.            return x + y
    3.        end
    5. julia> @cfunction(foo, Int, (Int, Int))
    6. Ptr{Cvoid} @0x000000001b82fcd0

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    — Type.

    1. CFunction struct

    Garbage-collection handle for the return value from @cfunction when the first argument is annotated with ‘$’. Like all cfunction handles, it should be passed to ccall as a Ptr{Cvoid}, and will be converted automatically at the call site to the appropriate type.

    See @cfunction.

    Base.unsafe_convert — Function.

    1. unsafe_convert(T, x)

    Convert x to a C argument of type T where the input x must be the return value of cconvert(T, ...).

    In cases where 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.

    See also cconvert

    Base.cconvert — Function.

    1. cconvert(T,x)

    Convert x to a value to be passed to C code as type T, typically by calling convert(T, x).

    In cases where x cannot be safely converted to T, unlike , cconvert may return an object of a type different from T, which however is suitable for unsafe_convert to handle. The result of this function should be kept valid (for the GC) until the result of is not needed anymore. This can be used to allocate memory that will be accessed by the ccall. If multiple objects need to be allocated, a tuple of the objects can be used as return value.

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

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    — Function.

    1. 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.

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    — Function.

    1. 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.

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    — Method.

    1. unsafe_copyto!(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.

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    — Method.

    1. unsafe_copyto!(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.

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    — Function.

    1. copyto!(dest, do, src, so, N)

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

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    1. copyto!(dest::AbstractArray, src) -> dest

    Copy all elements from collection src to array dest, whose length must be greater than or equal to the length n of src. The first n elements of dest are overwritten, the other elements are left untouched.

    Examples

    1. julia> x = [1., 0., 3., 0., 5.];
    3. julia> y = zeros(7);
    5. julia> copyto!(y, x);
    6. julia> y
    7. 7-element Array{Float64,1}:
    8.  1.0
    9.  0.0
    10.  3.0
    11.  0.0
    12.  5.0
    13.  0.0
    14.  0.0

    1. copyto!(dest, Rdest::CartesianIndices, src, Rsrc::CartesianIndices) -> dest

    Copy the block of src in the range of Rsrc to the block of dest in the range of Rdest. The sizes of the two regions must match.

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    1. copyto!(dest::AbstractMatrix, src::UniformScaling)

    Copies a onto a matrix.

    In Julia 1.0 this method only supported a square destination matrix. Julia 1.1. added support for a rectangular matrix.

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    — Function.

    Get the native address of an array or string, optionally at a given location index.

    This function is “unsafe”. Be careful to ensure that a Julia reference to array exists as long as this pointer will be used. The GC.@preserve macro should be used to protect the array argument from garbage collection within a given block of code.

    Calling is generally preferable to this function as it guarantees validity.

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    — Method.

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

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    — Function.

    1. pointer_from_objref(x)

    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.

    This function may not be called on immutable objects, since they do not have stable memory addresses.

    See also: unsafe_pointer_to_objref.

    Base.unsafe_pointer_to_objref — Function.

    1. 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.

    See also: .

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    — Function.

    1. 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:

    1. disable_sigint() do
    2.     # interrupt-unsafe code
    3.     ...
    4. 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.

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    — Function.

    1. reenable_sigint(f::Function)

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

    Base.systemerror — Function.

    1. systemerror(sysfunc, iftrue)

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

    Core.Ptr — Type.

    1. 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.

    Core.Ref — Type.

    1. 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.

    In Julia, Ref objects are dereferenced (loaded or stored) with [].

    Creation of a Ref to a value x of type T is usually written Ref(x). Additionally, for creating interior pointers to containers (such as Array or Ptr), it can be written Ref(a, i) for creating a reference to the i-th element of a.

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

    There is no invalid (NULL) Ref in Julia, but a C_NULL instance of Ptr can be passed to a ccall Ref argument.

    Use in broadcasting

    Broadcasting with Ref(x) treats x as a scalar:

    1. julia> isa.(Ref([1,2,3]), [Array, Dict, Int])
    2.  1
    3.  0
    4.  0

    Base.Cchar — Type.

    1. Cchar

    Equivalent to the native char c-type.

    Base.Cuchar — Type.

    1. Cuchar

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

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    — Type.

    1. Cshort

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

    Base.Cstring — Type.

    1. Cstring

    A C-style string composed of the native character type s. Cstrings are NUL-terminated. For C-style strings composed of the native wide character type, see Cwstring. For more information about string interopability with C, see the .

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    1. Cushort

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

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    — Type.

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

    Base.Cuint — Type.

    1. Cuint

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

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    — Type.

    1. Clong

    Equivalent to the native signed long c-type.

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    — Type.

    1. Culong

    Equivalent to the native unsigned long c-type.

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    — Type.

    1. Clonglong

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

    Base.Culonglong — Type.

    1. Culonglong

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

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    — Type.

    1. Cintmax_t

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

    Base.Cuintmax_t — Type.

    1. Cuintmax_t

    Equivalent to the native uintmax_t c-type ().

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    — Type.

    1. Csize_t

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

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    — Type.

    1. Cssize_t

    Equivalent to the native ssize_t c-type.

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    — Type.

    1. Cptrdiff_t

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

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    — Type.

    1. Cwchar_t

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

    Base.Cwstring — Type.

    1. Cwstring

    A C-style string composed of the native wide character type s. Cwstrings are NUL-terminated. For C-style strings composed of the native character type, see Cstring. For more information about string interopability with C, see the .

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    — Type.

    1. Cfloat

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

    Base.Cdouble — Type.

    1. Cdouble

    Equivalent to the native double c-type ().

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    LLVM Interface

    — Function.

    1. llvmcall(IR::String, ReturnType, (ArgumentType1, ...), ArgumentValue1, ...)
    2. llvmcall((declarations::String, IR::String), ReturnType, (ArgumentType1, ...), ArgumentValue1, ...)

    Call LLVM IR string in the first argument. Similar to an LLVM function define block, arguments are available as consecutive unnamed SSA variables (%0, %1, etc.).

    The optional declarations string contains external functions declarations that are necessary for llvm to compile the IR string. Multiple declarations can be passed in by separating them with line breaks.

    Note that the argument type tuple must be a literal tuple, and not a tuple-valued variable or expression.

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

    See for usage examples.

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