helloworld.cr

@[Link(ldflags: "#{__DIR__}/say.o")]
@[Link("m")]

lib LibSay 
  struct Person
    name : UInt8*
    height : UInt8*
    age  : Int32
  end

  fun hello_ptr(p : LibSay::Person*) : Void
  fun hello(p : LibSay::Person) : Void
end

p = LibSay::Person.new(name: "Isaac", age: 33, height: "5'11\"")

LibSay.hello_ptr(pointerof(p))
LibSay.hello(p)


lib LibMath
  fun pow(x : Float64, y : Float64) : Float64
end

puts LibMath.pow(2,3).to_i

say.c

#include <stdio.h>

typedef struct {
  char * name;
  char * height;
  int age;
} Person;


void hello_ptr(const Person * p){
 printf("Hello %s! Are you really %d and only %s tall?\n", p->name, p->age, p->height);
}

void hello(Person  p){
 printf("Hello %s! Are you really %d and only %s tall?\n", p.name, p.age, p.height);
}

gcc -c say.c && crystal build helloworld.cr