Test for i2c MCP23017 bus expander in C++ object

//Test for i2c mcp23017 bus expander Antonio Villanueva Segura
#include <iostream>
#include <fcntl.h>
#include <stdlib.h>     // exit
#include <linux/i2c-dev.h>//I2C_SLAVE
#include <sys/ioctl.h>//ioctl
#include <unistd.h> //read write usleep

#define I2C_ADDR 0x20 //Address mcp23017 expander
#define DEV_I2C "/dev/i2c-0" //device in linux /de

using namespace std;

class mcp23017{
    public:
    mcp23017();
    unsigned char I2CRead () ;//Read  GPIOA
    void I2CWrite (unsigned char data);//write GPIOB

    private:
    int fd;//file descriptor
    char buffer[2];//buffer[0] register ,buffer[1] data
    int I2COpen();//Try open file descriptor
    void I2CSetup (int fd);//Setup mcp23017
};
/*--------------------------------------------------------------------*/
    mcp23017::mcp23017(){
         fd=I2COpen();//Try open file descriptor
         if (fd<0){exit(0);}//fd error !
         I2CSetup (fd);//Setup mcp23017
        }
/*--------------------------------------------------------------------*/
    int mcp23017 ::I2COpen(){//Try open file descriptor

        fd = open(DEV_I2C, O_RDWR);//open file descriptor

        if (fd < 0) {//test fd
            cout <<"Error opening file: "<<DEV_I2C<<endl;
            return -1;
        }

        if (ioctl(fd, I2C_SLAVE, I2C_ADDR) < 0) {
            cout <<"ioctl error: "<<I2C_ADDR<<" "<< endl;
            return -1;
        }

        return fd;
    }
/*--------------------------------------------------------------------*/
    void mcp23017::I2CSetup (int fd){//Setup mcp23017

        buffer[1]=0x00;//Valeur register

        ////Clr.regs.mcp23017 IODIRB(0x01)=0x00 => GPIOB OUTPUT
        for( size_t reg=0x01 ;reg<0x10;reg++){
            buffer[0]=reg;//load register
            write(fd,buffer,2);
            usleep(1000);
        }

        //IODIRA (0x00)=0xFF => GPIOA INPUT
        buffer[0]=0x00;//Register IODIRA
        buffer[1]=0xFF;// Value INPUT
        write(fd,buffer,2);

    }

/*--------------------------------------------------------------------*/
    unsigned char  mcp23017::I2CRead () {//Read  GPIOA
        buffer[0]=0x12;//GPIOA
        write(fd,buffer,1);

        read(fd, &buffer[1], 1);
        return buffer[1];
    }
/*--------------------------------------------------------------------*/
    void mcp23017::I2CWrite ( unsigned char data){//write GPIOB
        buffer[0]=0x13;//GPIOB
        buffer[1]=data;
        write(fd,buffer,2);
    }

/*--------------------------------------------------------------------*/
/*--------------------------------------------------------------------*/
int main (){
    unsigned char data(0);//data for test outs
    unsigned char read(0);//read data from GPIOA

    mcp23017 strac;

    while (true){//Bucle test
        std::cout.flags ( std::ios::right | std::ios::hex | std::ios::showbase );
        std::cout.width (4);

        if (strac.I2CRead()!=read){//only show if I2CRead change !
            cout <<"INPUT GPIOA = " <<(int) (read=strac.I2CRead())<<endl;//Read GPIOA
        }
        usleep(500000);


        strac.I2CWrite (data++);//WRITE GPIOB
        usleep(500000);
    }

    return 0;
}