class_variable_defined?

/*
 *  call-seq:
 *     obj.class_variable_defined?(symbol)    => true or false
 *
 *  Returns <code>true</code> if the given class variable is defined
 *  in <i>obj</i>.
 *
 *     class Fred
 *       @@foo = 99
 *     end
 *     Fred.class_variable_defined?(:@@foo)    #=> true
 *     Fred.class_variable_defined?(:@@bar)    #=> false
 */

static VALUE
rb_mod_cvar_defined(obj, iv)
    VALUE obj, iv;
{
    ID id = rb_to_id(iv);

    if (!rb_is_class_id(id)) {
        rb_name_error(id, "`%s' is not allowed as a class variable name", rb_id2name(id));
    }
    return rb_cvar_defined(obj, id);
}