libTest.c

/** To be compiled with gcc -shared -o libTestJulia.so libTest.c -fPIC -L/usr/lib/julia/ -ljulia -std=gnu99 **/

#include <julia.h>
#include <string.h>
#include <stdio.h>

// returns a jl_array_t pointer
void * testJulia( void *thisModule )
{
    const char *str = "Hey it is me";

    jl_gc_disable();	// disable GC so we don't have to deal with POP/PUSH GC
    
    jl_value_t *msg = jl_pchar_to_string((char*)str, strlen(str));
    
    // get type 'MyType' from module
    jl_datatype_t *dtype = jl_get_global(thisModule, jl_symbol("MyType"));

    // allocate N-element double array
    const unsigned N = 131072000;
    jl_value_t* array_type = jl_apply_array_type(jl_float64_type, 1);
    jl_array_t* x          = jl_alloc_array_1d(array_type, N);

	// create 'uninitialized' type
    jl_value_t *ret = jl_new_struct_uninit( dtype );

    // fill in structure
    jl_set_nth_field( ret, 0, msg );
    jl_set_nth_field( ret, 1, jl_box_int64(231) );
    jl_set_nth_field( ret, 2, x );

    jl_gc_enable();	// very important before returning

    return ret;
}

test.jl

module MyModule

# sample structure to be filled by ccall
type MyType
    msg::String
    num::Int64
    arr::Array

    MyType() = new()
end

# the ccall will feed MyType
function test()
	ret = ccall( (:testJulia, "./libTestJulia.so"), Any, (Ptr{Void},), (pointer_from_objref(MyModule)) )
end


end