Ruby Language C Extensions Working with C Structs
Example
In order to be able to work with C structs as Ruby objects, you need to wrap them with calls to Data_Wrap_Struct and Data_Get_Struct.
Data_Wrap_Struct wraps a C data structure in a Ruby object. It takes a pointer to your data structure, along with a few pointers to callback functions, and returns a VALUE. The Data_Get_Struct macro takes that VALUE and gives you back a pointer to your C data structure.
Here's a simple example:
#include <stdio.h>
#include <ruby.h>
typedef struct example_struct {
char *name;
} example_struct;
void example_struct_free(example_struct * self) {
if (self->name != NULL) {
free(self->name);
}
ruby_xfree(self);
}
static VALUE rb_example_struct_alloc(VALUE klass) {
return Data_Wrap_Struct(klass, NULL, example_struct_free, ruby_xmalloc(sizeof(example_struct)));
}
static VALUE rb_example_struct_init(VALUE self, VALUE name) {
example_struct* p;
Check_Type(name, T_STRING);
Data_Get_Struct(self, example_struct, p);
p->name = (char *)malloc(RSTRING_LEN(name) + 1);
memcpy(p->name, StringValuePtr(name), RSTRING_LEN(name) + 1);
return self;
}
static VALUE rb_example_struct_name(VALUE self) {
example_struct* p;
Data_Get_Struct(self, example_struct, p);
printf("%s\n", p->name);
return Qnil;
}
void Init_example()
{
VALUE mExample = rb_define_module("Example");
VALUE cStruct = rb_define_class_under(mExample, "Struct", rb_cObject);
rb_define_alloc_func(cStruct, rb_example_struct_alloc);
rb_define_method(cStruct, "initialize", rb_example_struct_init, 1);
rb_define_method(cStruct, "name", rb_example_struct_name, 0);
}
And the extconf.rb:
require 'mkmf'
create_makefile('example')
After compiling the extension:
irb(main):001:0> require './example'
=> true
irb(main):002:0> test_struct = Example::Struct.new("Test Struct")
=> #<Example::Struct:0x007fc741965068>
irb(main):003:0> test_struct.name
Test Struct
=> nil
