Hi, I'm having a problem wrapping the Rabbit MQ C client library (<a href="https://github.com/alanxz/rabbitmq-c">https://github.com/alanxz/rabbitmq-c</a>) using the ffi. My problem is with the amqp_queue_declare function. The C declaration is: amqp_queue_declare_ok_t * amqp_queue_declare(amqp_connection_state_t state, amqp_channel_t channel, amqp_bytes_t queue, amqp_boolean_t passive, amqp_boolean_t durable, amqp_boolean_t exclusive, amqp_boolean_t auto_delete, amqp_table_t arguments); It seems to run successfully when wrapped to return an opaque pointer: (define _amqp-queue-declare-ok-pointer (_cpointer 'QUEUE-DECLARE-OK)) (define-amqp amqp_queue_declare (_fun _amqp-connection-state-pointer _amqp_channel_t _pointer _int _int _int _int _pointer -> _amqp-queue-declare-ok-pointer)) > #<cpointer:QUEUE-DECLARE-OK> Wrapping it to return a cstruct pointer fails with a SEGV. > SIGSEGV MAPERR si_code 1 fault on addr (nil) The wrapping code for the c structs is as follows: (define _size_t _uint32) (define _amqp_channel_t _uint16) (define-cstruct _amqp_bytes_t ([len _size_t] [bytes _pointer])) ;; c definition of amqp_bytes_t is: ;; typedef struct amqp_bytes_t_ { ;; size_t len; ;; void *bytes; ;; } amqp_bytes_t; (define-cstruct _amqp_queue_declare_ok_t ([queue _amqp_bytes_t] [message_count _uint32] [consumer_count _uint32])) ;; typedef struct amqp_queue_declare_ok_t_ { ;; amqp_bytes_t queue; ;; uint32_t message_count; ;; uint32_t consumer_count; ;; } amqp_queue_declare_ok_t; (define-amqp amqp_queue_declare (_fun _amqp-connection-state-pointer _amqp_channel_t _pointer _int _int _int _int _pointer -> _amqp_queue_declare_ok_t)) Any ideas what I'm doing wrong here? The full code so far is below: #lang racket/base (require ffi/unsafe ffi/unsafe/define) (define lib-rabbit-mq (ffi-lib "librabbitmq")) (define-ffi-definer define-amqp lib-rabbit-mq) ;; C types (define _size_t _uint32) (define _amqp_channel_t _uint16) (define-cstruct _amqp_bytes_t ([len _size_t] [bytes _pointer])) (define-cstruct _amqp_queue_declare_ok_t ([queue _amqp_bytes_t] [message_count _uint32] [consumer_count _uint32])) (define-cstruct _amqp_method_t ([id _uint32] [decoded _pointer])) (define-cstruct _amqp_rpc_reply_t ([reply_type _int] [reply _amqp_method_t] [library_error _int])) (define _amqp-connection-state-pointer (_cpointer 'CONNECTION-STATE)) (define _amqp-channel-open_ok-pointer (_cpointer 'CHANNEL-OPEN-OK)) ;; C functions (define-amqp amqp_error_string (_fun _int -> _string)) (define-amqp amqp_get_rpc_reply (_fun _amqp-connection-state-pointer -> _amqp_rpc_reply_t)) (define-amqp amqp_new_connection (_fun -> _amqp-connection-state-pointer)) (define-amqp amqp_open_socket (_fun _string _int -> _int)) (define-amqp amqp_set_sockfd (_fun _amqp-connection-state-pointer _int -> _int)) (define-amqp amqp_login (_fun _amqp-connection-state-pointer _string _int _int _int _int _string _string -> _amqp_rpc_reply_t)) (define-amqp amqp_channel_open (_fun _amqp-connection-state-pointer _amqp_channel_t -> _amqp-channel-open_ok-pointer)) ;; *** THIS DOES NOT WORK (define-amqp amqp_queue_declare (_fun _amqp-connection-state-pointer _amqp_channel_t _pointer _int _int _int _int _pointer -> _amqp_queue_declare_ok_t)) ;; *** THIS SEEMS TO WORK (define _amqp-queue-declare-ok-pointer (_cpointer 'QUEUE-DECLARE-OK)) (define-amqp amqp_queue_declare (_fun _amqp-connection-state-pointer _amqp_channel_t _pointer _int _int _int _int _pointer -> _amqp-queue-declare-ok-pointer)) ;; main (define conn (amqp_new_connection)) (define sockfd (amqp_open_socket "localhost" 5672)) (when (< sockfd 0) (amqp_error_string (* -1 sockfd))) (amqp_set_sockfd conn sockfd) (define *AMQP_SASL_METHOD_PLAIN* 0) (define resp (amqp_login conn "/" 0 131072 0 *AMQP_SASL_METHOD_PLAIN* "user" "pwd")) (amqp_channel_open conn 1) (amqp_queue_declare conn 1 #f 0 0 0 1 #f)