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cglobal

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.

Examples

In the Julia programming language, the function cglobal((symbol, library) [, type=Void]) is used to obtain a pointer to a global variable in a C-exported shared library. The function signature is as follows:

cglobal((symbol, library) [, type=Void]) -> Ptr{Type}

Here are some examples of how to use the cglobal function:

1. Access a global integer variable:

   julia> cglobal((:my_global_int, "mylibrary"), Cint)
   Ptr{Cint} @0x00007f9d23b20140

   This example obtains a pointer to the global integer variable my_global_int in the shared library "mylibrary". The type of the variable is specified as Cint.

2. Access a global float variable:

   julia> cglobal((:my_global_float, "mylibrary"), Cfloat)
   Ptr{Cfloat} @0x00007f9d23b20160

   This example obtains a pointer to the global float variable my_global_float in the shared library "mylibrary". The type of the variable is specified as Cfloat.

3. Access a global variable with default type (Ptr{Void}):

   julia> cglobal((:my_global_var, "mylibrary"))
   Ptr{Void} @0x00007f9d23b20180

   If no type argument is supplied, the cglobal function returns a pointer of type Ptr{Void} by default. In this example, we obtain a pointer to the global variable my_global_var in the shared library "mylibrary".

Common mistake example:

julia> cglobal((:nonexistent_var, "mylibrary"))
ERROR: could not find symbol "nonexistent_var" in library "mylibrary"

In this example, the function call fails because the symbol nonexistent_var does not exist in the specified library. Make sure to provide the correct symbol name and ensure that the library contains the desired global variable.

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