Need help on go1.8 cgo compilation error

[clashion]

Hi, 

I tried to compile the code from https://github.com/ebfe/scard .

Error during compilation.

Environment: go1.8 , linux

Error Message:

cgo-gcc-prolog:198:2: warning: passing argument 3 of ‘SCardGetStatusChange’ from incompatible pointer type [enabled by default]

/usr/include/PCSC/winscard.h:64:16: note: expected ‘LPSCARD_READERSTATE’ but argument is of type ‘struct *’
PCSC_API LONG SCardGetStatusChange(SCARDCONTEXT hContext,

Need advice how to solve this. Thanks.

[Ian Lance Taylor]

You are using cgo code. This error comes from the C compiler. You
need to use the correct type in your C code.

Ian

[clas...@gmail.com]

I think the correct C type is used. 

refer: https://github.com/ebfe/scard/blob/master/scard_unix.go 

Line 57:

func scardGetStatusChange(ctx uintptr, timeout uint32, states []scardReaderState) Error {
       r := C.SCardGetStatusChange(C.SCARDCONTEXT(ctx), C.DWORD(timeout), (C.LPSCARD_READERSTATE)(unsafe.Pointer(&states[0])), C.DWORD(len(states)))
       return Error(r)

[clas...@gmail.com]

The reason I think correct C type is used is because in the "winscard.h" C header file, the expected type is LPSCARD_READERSTATE.

And , in the golang cgo code, i.e. scard_unix.go, the argument 3 is cast as (C.LPSCARD_READERSTATE).

Further details (not sure if is useful): 

I found that in another C header file (pcsclite.h),  LPSCARD_READERSTATE is defined as:

typedef struct

{

        const char *szReader;

        void *pvUserData;

        DWORD dwCurrentState;

        DWORD dwEventState;

        DWORD cbAtr;

        unsigned char rgbAtr[MAX_ATR_SIZE];

}

SCARD_READERSTATE, *LPSCARD_READERSTATE;

And, on Windows , I could compile the code but failed on linux. 

[Ian Lance Taylor]

On Mon, Apr 3, 2017 at 7:20 PM, <clas...@gmail.com> wrote:
> The reason I think correct C type is used is because in the "winscard.h" C
> header file, the expected type is LPSCARD_READERSTATE.
> And , in the golang cgo code, i.e. scard_unix.go, the argument 3 is cast as
> (C.LPSCARD_READERSTATE).
>
>
>
>
> Further details (not sure if is useful):
> I found that in another C header file (pcsclite.h), LPSCARD_READERSTATE is
> defined as:
> typedef struct
> {
> const char *szReader;
> void *pvUserData;
> DWORD dwCurrentState;
> DWORD dwEventState;
> DWORD cbAtr;
> unsigned char rgbAtr[MAX_ATR_SIZE];
> }
> SCARD_READERSTATE, *LPSCARD_READERSTATE;
>
>
> And, on Windows , I could compile the code but failed on linux.

The Windows code is different anyhow. The file that fails is not
compiled on Windows.

Anyhow, I do see this now. Thanks for the report. Filed
https://golang.org/issue/19832.

It's just a warning, so the immediate workaround is to simply ignore
the problem.

Another workaround would be to modify the Go code to not call
`C.SCardGetStatusChange` directly, but to call a little function,
defined in the C comment, that takes a void* argument and calls the
real C function.

Ian

[Nicholas]

Got it. Thanks.