The macro SPI_IOC_MESSAGE (N) gives me the opportunity

Question

I am having trouble getting the SPI program I'm working on to behave correctly, and it seems to be a problem with the SPI_IOC_MESSAGE (N) macro.

Here's an example of code that DOES NOT work (ioctl returns EINVAL (22)):

std::vector<spi_ioc_transfer> tr;
<code that fills tr with 1+ transfers>
// Hand the transmission(s) off to the SPI driver
if (tr.size() > 0)
{
    int ret = ioctl(fd, SPI_IOC_MESSAGE(tr.size()), tr.data());
    if (ret < 1)
    {
         int err = errno;
    }
}

My test code is now creating a vector of length 1. If I explicitly changed the code to:

int ret = ioctl(fd, SPI_IOC_MESSAGE( 1 ), tr.data());

... then ioctl (...) succeeds, and my bits go through the pipe. If you look at the macro extension SPI_IOC_MESSAGE in Eclipse, I don’t understand why this is not good.

Suggestions?

I cross-compile for Linux / ARM (Beaglebone Black) from a 64-bit Linux virtual machine, but I don’t see that this affects the macro.

EDIT: Here are two macro extensions from the C preprocessor

int ret = ioctl(fd, (((1U) << (((0 +8)+8)+14)) | ((('k')) << (0 +8)) | (((0)) << 0) | ((((sizeof(char[((((tr.size())*(sizeof (struct spi_ioc_transfer))) < (1 << 14)) ? ((tr.size())*(sizeof (struct spi_ioc_transfer))) : 0)])))) << ((0 +8)+8))), tr.data());

and the letter:

int ret = ioctl(fd, (((1U) << (((0 +8)+8)+14)) | ((('k')) << (0 +8)) | (((0)) << 0) | ((((sizeof(char[((((1)*(sizeof (struct spi_ioc_transfer))) < (1 << 14)) ? ((1)*(sizeof (struct spi_ioc_transfer))) : 0)])))) << ((0 +8)+8))), tr.data());

, , tr.size() .

, ,

#ifdef __cplusplus /* If this is a C++ compiler, use C linkage */
extern "C" {
#endif
#include <linux/spi/spidev.h>
#ifdef __cplusplus /* If this is a C++ compiler, use C linkage */
}
#endif

linux SPI include "extern C" C, , , SPI_IOC_MESSAGE( tr.size() ) SPI_IOC_MESSAGE( an_int ) ( GDB ).

Answer 1

, , :

...sizeof(char[...tr.size()...])...

, Linux C, C ( C99 n1256 ) sizeof, , , , , .

++ ( ++ 11 n3242), , , , , , .

, , , C ++ , undefined. , - C, .