Calling C and Fortran

While Julia can rightfully claim to obviate the need to write some C or Fortran code, it is possible that you will need to interact with the existing C or Fortran shared libraries. Functions in such a library can be called directly by Julia, with no glue code, boilerplate code, or compilation needed. Because Julia's LLVM compiler generates native code, calling a C function from Julia has exactly the same overhead as calling the same function from C code itself. However, first, we need to know a few more things:

• For calling out to C, we need to work with pointer types; a native pointer Ptr{T} is nothing more than the memory address for a variable of type T. You can use Cstring if the value is null-terminated.
• At this lower level, the term primitive is also used. primitive is a concrete type whose data consists of bits, such as Int8, UInt8, Int32, Float64, Bool, and Char.
• To pass a string to C, it is converted to a contiguous byte array representation with the function unsafe_string...