Using strpack.jl as an FFI

README.md

Note

strpack.jl is deprecated. Use the StrPack package or Julia's native C struct interop instead, depending on your needs.

Using strpack.jl as an FFI

This gist demonstrates calling C code which expects a structure pointer by writing and reading a buffer using the functions provided by strpack.jl. This takes advantage of the new align_native alignment strategy, which queries libLLVM for the platform-preferred alignment of the standard bits types.

Build the shared library

gcc -Wall -fPIC -c *.c
cc -shared -Wl,-soname,libtest.so -o libtest.so *.o

Show the result of calling the shared library from Julia

julia> load("struct_test.jl")

julia> foo
Foo(1,4.0,0x07)

julia> foo2
Foo(2,11.0,0x06)

struct_test.c

#include <stdint.h>

typedef struct {
    int32_t bar;
    double baz;
    uint8_t bat;
} foo;

void foobar(foo* x) {
    x->bar++;
    x->baz = x->baz + (double)(x->bat);
    x->bat--;
}

struct_test.jl

load("strpack.jl")

type Foo
    bar::Int32
    baz::Float64
    bat::Uint8
end

const libtest = dlopen("libtest.so")

foo = Foo(int32(1), 4.0, uint8(7))
foobuf = pack(foo, align_native)
ccall(dlsym(libtest, :foobar), Void, (Ptr{Uint8},), foobuf.data)
seek(foobuf, 0)
foo2 = unpack(foobuf, Foo, align_native)