foo.c

#include <stdio.h>
#include <stdlib.h>

__declspec(dllexport) void Argless()
{
    printf ("Hello from argless function!\n");
}

__declspec(dllexport) void GotValues(int x, float y, char *z1)
{
    printf ("Hello from DLL; have %d, %f and %s\n", x, y, z1);
}

struct foo {
    double x;
    long long y;
    double z;
};

__declspec(dllexport) void WithStruct(struct foo *s)
{
    printf ("Got struct with %f, %d, %f\n", s->x, s->y, s->z);
}

__declspec(dllexport) void IDiddleTheStruct(struct foo *s)
{
    s->x = 99.99;
}

__declspec(dllexport) char * ReturnAString()
{
    return "A string from C!";
}

__declspec(dllexport) struct foo * ReturnAStruct()
{
    struct foo *f = malloc(sizeof(struct foo));
    f->x = 123.45;
    f->y = 101;
    f->z = 789.10;
    return f;
}

nc.p6

use NativeCall;

##
## Some simple calls.
##

sub Argless() is native('foo.dll') { * }
Argless();

sub GotValues(int, num32, Str) is native('foo.dll') { * }
GotValues(42, 1.23e0, 'oh hai');

##
## Declare a class with C structure representation and pass it.
##

class foo is repr('CStruct') {
    has num $.x;
    has int $.y;
    has num $.z;
    method set(num $x, int $y, num $z) {
        $!x = $x;
        $!y = $y;
        $!z = $z;
    }
}

sub WithStruct(foo) is native("foo.dll") { * }
my $s = foo.new();
$s.set(2.5e0, 42, 10.1e0);
WithStruct($s);

sub IDiddleTheStruct(foo) is native("foo.dll") { * }
say "Before: $s.x()";
IDiddleTheStruct($s);
say "After: $s.x()";

##
## We can get string and struct return values.
##

sub ReturnAString() returns Str is native("foo.dll") { * }
say ReturnAString();

sub ReturnAStruct() returns foo is native("foo.dll") { * }
my $rs = ReturnAStruct();
say "Got back struct with $rs.x(), $rs.y(), $rs.z()";

##
## Example of calling the Windows API.
##

sub MessageBoxA(Int, Str, Str, Int) returns Int is native('user32.dll') { * }
say "MessageBoxA returned " ~ MessageBoxA(0, "Hi from Rakudo", "NCI", 0x40);

output

Hello from argless function!
Hello from DLL; have 42, 1.230000 and oh hai
Got struct with 2.500000, 42, 10.100000
Before: 2.5
After: 99.99
A string from C!
Got back struct with 123.45, 101, 789.1
MessageBoxA returned 1