<div dir="ltr">Hi, I'm wrapping Win32 PC/SC and I don't understand how I should wrap structures. Here is my simplified header: ============= C HEADER ============= #define IN /* Tag for INPUT parameters */ #define OUT /* Tag for OUTPUT parameters */   typedef int DWORD; typedef int LONG; typedef LONG SCARDHANDLE; typedef unsigned char BYTE; typedef const BYTE* LPCBYTE; typedef DWORD* LPDWORD; typedef struct _SCARD_IO_REQUEST{     DWORD dwProtocol;   // Protocol identifier     DWORD cbPciLength;  // Protocol Control Information Length } SCARD_IO_REQUEST, *PSCARD_IO_REQUEST, *LPSCARD_IO_REQUEST; typedef const SCARD_IO_REQUEST *LPCSCARD_IO_REQUEST; LONG SCardTransmit(     IN SCARDHANDLE hCard,     IN LPCSCARD_IO_REQUEST pioSendPci,     IN LPCBYTE pbSendBuffer,     IN DWORD cbSendLength,     IN OUT LPSCARD_IO_REQUEST pioRecvPci,     OUT LPBYTE pbRecvBuffer,     IN OUT LPDWORD pcbRecvLength); ============= END OF C HEADER ============= Here is my conversion attempt: ============= SCHEME MODULE  ============= ;; #lang mzscheme (module winscard mzscheme   (require mzlib/foreign)   (unsafe!)     (define winscard (ffi-lib "winscard"))     (define _DWORD _int)   (define _LONG _int)   (define _SCARDHANDLE _int)     (provide scard-ok)   (define (scard-ok scard-error)     (= scard-error 0))   (provide make-SCARD_IO_REQUEST)   (define-cstruct _SCARD_IO_REQUEST ([dwProtocol _DWORD];;   // Protocol identifier                                      [cbPciLength _DWORD])) ;;  // Protocol Control Information Length     #| LONG SCardTransmit(     IN SCARDHANDLE hCard,     IN LPCSCARD_IO_REQUEST pioSendPci,     IN LPCBYTE pbSendBuffer,     IN DWORD cbSendLength,     IN OUT LPSCARD_IO_REQUEST pioRecvPci,     OUT LPBYTE pbRecvBuffer,     IN OUT LPDWORD pcbRecvLength); |#   (provide scard-transmit)   (define scard-transmit     (get-ffi-obj "SCardTransmit"                  winscard                  (_fun (hCard : _SCARDHANDLE) ;; == IN SCARDHANDLE hCard                        (pioSendPci : _SCARD_IO_REQUEST-pointer) ;; == IN LPCSCARD_IO_REQUEST pioSendPci                        (pbSendBuffer : (_vector i _byte)) ;; == IN LPCBYTE pbSendBuffer                        (cbSendLength : _DWORD) ;; == IN DWORD cbSendLength                        (ioRecvPci : (_ptr io _SCARD_IO_REQUEST)) ;; == IN OUT LPSCARD_IO_REQUEST pioRecvPci                        (pbRecvBuffer :  (_vector o _byte cbRecvLength)) ;; == OUT LPBYTE pbRecvBuffer                        (cbRecvLength : (_ptr io _DWORD)) ;; == IN OUT LPDWORD pcbRecvLength                        -> (error : _LONG)                        -> (if (scard-ok error) '(error ioRecvPci pbRecvBuffer cbRecvLength) #f)                        )))     ) ============= END OF SCHEME MODULE  ============= ============= SCHEME PROGRAM  ============= (require "winscard.ss") (require mzlib/foreign) (unsafe!) (define hCard 1) (define pioSendPci (make-SCARD_IO_REQUEST #x0002 8)) (define pbSendBuffer (make-vector 4 0)) (define cbSendLength 4) (define ioRecvPci (make-SCARD_IO_REQUEST #x0002 8)) (define cbRecvLength 4) (scard-transmit  hCard  pioSendPci  pbSendBuffer  cbSendLength  ioRecvPci  ;; pbRecvBuffer skipped since it's an output parameter  cbRecvLength) ============= END OF SCHEME PROGRAM  ============= Program fails with: "zero?: expects argument of type <real number>; given #<cpointer>". Any hint? Thanks. </div>