write code for spi communication using c/c++

Sure, here's an example code for SPI communication using C/C++:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/spi/spidev.h>

#define SPI_DEVICE "/dev/spidev0.0"
#define SPI_MODE SPI_MODE_0
#define SPI_BITS_PER_WORD 8
#define SPI_SPEED_HZ 1000000

int spi_fd;

int spi_init()
{
    int ret = 0;

    spi_fd = open(SPI_DEVICE, O_RDWR);
    if (spi_fd < 0) {
        perror("open");
        return -1;
    }

    uint8_t mode = SPI_MODE;
    ret = ioctl(spi_fd, SPI_IOC_WR_MODE, &mode);
    if (ret < 0) {
        perror("ioctl");
        return -1;
    }

    uint8_t bits_per_word = SPI_BITS_PER_WORD;
    ret = ioctl(spi_fd, SPI_IOC_WR_BITS_PER_WORD, &bits_per_word);
    if (ret < 0) {
        perror("ioctl");
        return -1;
    }

    uint32_t speed_hz = SPI_SPEED_HZ;
    ret = ioctl(spi_fd, SPI_IOC_WR_MAX_SPEED_HZ, &speed_hz);
    if (ret < 0) {
        perror("ioctl");
        return -1;
    }

    return 0;
}

int spi_transfer(uint8_t *tx_buf, uint8_t *rx_buf, size_t len)
{
    struct spi_ioc_transfer transfer = {
        .tx_buf = (unsigned long)tx_buf,
        .rx_buf = (unsigned long)rx_buf,
        .len = len,
        .speed_hz = SPI_SPEED_HZ,
        .bits_per_word = SPI_BITS_PER_WORD,
        .delay_usecs = 0,
    };

    int ret = ioctl(spi_fd, SPI_IOC_MESSAGE(1), &transfer);
    if (ret < 0) {
        perror("ioctl");
        return -1;
    }

    return 0;
}

int main()
{
    int ret = spi_init();
    if (ret < 0) {
        printf("SPI initialization failed\n");
        return -1;
    }

    uint8_t tx_buf[2] = {0x01, 0x02};
    uint8_t rx_buf[2] = {0};

    ret = spi_transfer(tx_buf, rx_buf, 2);
    if (ret < 0) {
        printf("SPI transfer failed\n");
        return -1;
    }

    printf("Received data: 0x%02x 0x%02x\n", rx_buf[0], rx_buf[1]);

    close(spi_fd);

    return 0;
}

This code initializes the SPI device and performs a SPI transfer with a 2-byte transmit buffer and a 2-byte receive buffer. The received data is printed to the console.