unicode string in C extension

I am writing a C extension for Ruby, and I need to accept a string as a parameter, and iterate the characters in the string. My code below works fine for ASCII characters, but it does not handle multiple byte characters, and outputs "garbage" instead. I could not find any sample code that would iterate over unicode strings. I would appreciate any pointers.

static VALUE test_method(VALUE self, VALUE text)
{
    char *pch;
    char *pch_end = RSTRING_END(text);

    for (pch = RSTRING_PTR(text); pch < pch_end; pch++)
    {
        printf("%c\n", *pch);
    }
    ...
}