Better I2CBus.cpp. I want to integrate this into minimu9-ahrs.

I2CBus.cpp

#include "I2CBus.h"
#include <cerrno>
#include <cstring>
#include <system_error>
#include <string>
#include <unistd.h>
#include <fcntl.h>
#include <linux/i2c-dev.h>

static inline std::system_error posix_error(const std::string & what)
{
    return std::system_error(errno, std::system_category(), what);
}

I2CBus::I2CBus(const char * deviceName)
{
    fd = open(deviceName, O_RDWR);
    if (fd == -1)
    {
        throw posix_error(std::string("Failed to open I2C device ") + deviceName);
    }
}

I2CBus::~I2CBus()
{
    close(fd);
}

void I2CBus::writeByteAndRead(uint8_t deviceAddress, uint8_t command, uint8_t size, uint8_t * data)
{
    i2c_msg messages[2] = {
      { deviceAddress, 0, 1, (typeof(i2c_msg().buf)) &command },
      { deviceAddress, I2C_M_RD, size, (typeof(i2c_msg().buf)) data },
    };
    i2c_rdwr_ioctl_data ioctl_data = { messages, 2 };

    int result = ioctl(fd, I2C_RDWR, &ioctl_data);

    if (result != 2)
    {
        throw posix_error("Failed to read from I2C");
    }
}

void I2CBus::write(uint8_t deviceAddress, uint8_t size, const uint8_t * data)
{
    i2c_msg message = { deviceAddress, 0, size, (typeof(i2c_msg().buf)) data };
    i2c_rdwr_ioctl_data ioctl_data = { &message, 1 };

    int result = ioctl(fd, I2C_RDWR, &ioctl_data);

    if (result != 1)
    {
        throw posix_error("Failed to write to I2C");
    }
}

I2CBus.h

#pragma once

#include <stdint.h>

class I2CBus
{
public:
    I2CBus(const char * deviceName);
    ~I2CBus();

    void writeByteAndRead(uint8_t deviceAddress, uint8_t byte,
      uint8_t size, uint8_t * data);
    void write(uint8_t deviceAddress, uint8_t size, const uint8_t * data);

    void writeTwoBytes(uint8_t deviceAddress, uint8_t byte1, uint8_t byte2)
    {
        uint8_t buffer[] = { byte1, byte2 };
        write(deviceAddress, 2, buffer);
    }

    uint8_t writeByteAndReadByte(uint8_t deviceAddress, uint8_t byte1)
    {
        uint8_t byte2;
        writeByteAndRead(deviceAddress, byte1, 1, &byte2);
        return byte2;
    }

    // TODO:
    //int tryWriteByteAndReadByte(uint8_t deviceAddress, uint8_t byte1);

private:
    int fd;
};